@Article{aph23p49,
author = "Z. Kurucz and P. Adam and J. Janszky",
title = "Simulating Measurement Statistics in Remote State Preparation",
journal = "Acta Phys. Hung. B",
year = {2005},
volume = 23,
number = "12",
page = "4954",
url = "http://optics.szfki.kfki.hu/~kurucz/downloads/aph23p49.pdf",
abstract = "Exact deterministic remote state preparation schemes that
involve projective measurements on Alices side are not able to prepare
arbitrary states but a restricted ensemble of states only. Instead of
restoring the output state, Bob can transform his future measuring
devices, and he can get the same probability amplitudes as with the
original state. We show that such a simulation of measurement statistics
is not possible for arbitrary states."
}
@Article{pra73e062301,
title = "General criterion for oblivious remote state preparation",
author = "Z. Kurucz and P. Adam and J. Janszky",
journal = "Phys. Rev. A",
year = {2006},
volume = 73,
number = 6,
pages = 062301,
eprint = "quant-ph/0605057",
url = "http://link.aps.org/abstract/PRA/v73/e062301",
abstract = "A necessary and sufficient condition is given for general exact remote state preparation (RSP) protocols to be oblivious, that is, no information about the target state can be retrieved from the classical message. A criterion in terms of commutation relations is also derived for the existence of deterministic exact protocols in which Alice's measurement eigenstates are related to each other by fixed linear operators similar to Bob's unitaries. For nonmaximally entangled resources, it provides an easy way to search for RSP protocols. As an example, we show how to reduce the case of partially entangled resources to that of maximally entangled ones, and we construct RSP protocols exploiting the structure of the irreducible representations of Abelian groups."
}
@Article{HiesmayrKN06,
author = {Beatrix C. Hiesmayr and Matyas Koniorczyk and Heide Narnhofer},
title = {Maximizing nearest-neighbor entanglement in finitely correlated qubit chains},
journal = {Phys. Rev. A},
year = {2006},
volume = {73},
number = {3},
pages = {032310},
month = {March},
abstract = {
We consider translationally invariant states of an infinite
one-dimensional chain of qubits or spin-1/2 particles. We maximize the
entanglement shared by nearest neighbors via a variational approach
based on finitely correlated states. We find an upper bound of
nearest-neighbor concurrence equal to C=0.434 095 which is 0.09% away
from the bound CW=0.434 467 obtained by a completely different
procedure. The obtained state-maximizing nearest-neighbor entanglement
seems to approximate the maximally entangled mixed states. Further we
investigate in detail several other properties of the so-obtained
optimal state.},
URL = {http://link.aps.org/doi/10.1103/PhysRevA.73.032310}
}
@Article{KoniorczykBA06,
author = {M. Koniorczyk and V. Buzek and P. Adam},
title = {Simulation of generators of Markovian dynamics on programmable quantum processors},
journal = {Eur. Phys. J. D},
year = {2006},
volume = {37},
number = {2},
pages = {275-281},
month = {February},
abstract = {We study how generators of Markovian dynamics of a qubit can be simulated using a programmable quantum processor.},
URL = {http://dx.doi.org/10.1140/epjd/e2005-00286-2}
}
@Article{job7p135,
author = "Z. Kurucz and P. Adam",
title = "Preparable ensembles for remote state preparation",
journal = "J. Opt. B: Quantum Semiclass. Opt.",
year = 2005,
month = "May",
volume = 7,
number = 5,
pages = "135-138",
doi = "doi:10.1088/1464-4266/7/5/002",
url = "http://optics.szfki.kfki.hu/~kurucz/downloads/job7p135.pdf",
abstract = "We determine all the ensembles that can be remotely prepared
in a deterministic and oblivious way using a nonmaximally entangled
resource with minimum classical communication cost when Bobs unitary
transformations form a cyclic group. We show that the classical
communication has maximal informational entropy. We also give a
constraint for the shared entangled resource that can be used for remote
state preparation."
}
@Article{pra72e052315,
author = "Z. Kurucz and P. Adam and Z. Kis and J. Janszky",
title = "Continuous variable remote state preparation",
journal = "Phys. Rev A",
year = {2005},
volume = 72,
number = 5,
pages = 052315,
url = "http://optics.szfki.kfki.hu/~kurucz/downloads/pra72e052315.pdf",
abstract = "We extend exact deterministic remote state preparation (RSP)
with minimal classical communication to quantum systems of continuous
variables. We show that, in principle, it is possible to remotely
prepare states of an ensemble that is parametrized by infinitely many
real numbers---i.e., by a real function---while the classical
communication cost is one real number only. We demonstrate continuous
variable RSP in three examples using (i) quadrature measurement and
phase-space displacement operations, (ii) measurement of the optical
phase and unitaries shifting the same, and (iii) photon counting and
photon number shift."
}
@article{KissL04,
number = {5},
volume = {6},
month = {May},
author = {T. Kiss and U. Leonhardt},
title = {Towards a classification of wave catastrophes},
abstract = {Wave catastrophes are characterized by logarithmic
phase singularities. Examples are light at the horizon of a black
hole, sound in transsonic fluids, waves in accelerated frames, light
in singular dielectrics and slow light close to a zero of the group
velocity. We show that the wave amplitude grows with a half-integer
power for monodirectional and symmetric wave catastrophes.},
year = {2004},
pages = {S246-S247},
journal = {J. Opt. A: Pure Appl. Opt.},
}
@article{GiovanazziFKL04,
number = {6},
volume = {70},
month = {December},
author = {S. Giovanazzi and C. Farrell and T. Kiss and U. Leonhardt},
title = {Conditions for one-dimensional supersonic flow of quantum
gases},
abstract = { One can use transsonic Bose-Einstein condensates of
alkali atoms to establish the laboratory analog of the event horizon
and to measure the acoustic version of Hawking radiation. We
determine the conditions for supersonic flow and the Hawking
temperature for realistic condensates on waveguides where an external
potential plays the role of a supersonic nozzle. The transition to
supersonic speed occurs at the potential maximum and the Hawking
temperature is entirely determined by the curvature of the potential.},
year = {2004},
pages = {063602},
journal = {Phys. Rev. A}
}
@Article{zippilli04,
author = {S. Zippilli and J. Asboth and G. Morigi and H. Ritsch},
title = {Forces and spatial ordering of driven atoms in a
resonator in the regime of fluorescence suppression},
journal = {Appl. Phys. B: Lasers and Optics},
year = {2004},
volume = {79},
number = {8},
pages = {969-978},
month = {December},
abstract = { An atom in a high-Q cavity, which is coherently driven at
the frequency of a cavity mode, exhibits strong suppression of
fluorescence when the atomic decay rate exceeds the cavity linewidth. This
effect is due to destructive interference of cavity and pump field, such
that at the atomic position the total field intensity has a local minimum.
For atomic ensembles the magnitude of the interference effect grows with
atom number and depends on the relative atomic positions. It is strongest
for a wavelength spaced array of atoms placed at the antinodes of the
cavity mode. This suppresses fluorescence and enhanced collective
scattering into the cavity mode. We analyze the mechanical forces in the
regime where the interference condition is fulfilled. We show that the
atomic pattern is mechanically stable whenever the driving frequency is
red detuned with respect to the cavity frequency, irrespective of the
atomic transition frequency. Hence atomic selforganization, as predicted
in [6] can also occur in the parameter regime where superradiant
scattering is suppressed by collective interference.}
}
@Article{nonc05,
author = {J. K. Asboth and J. Calsamiglia and H. Ritsch},
title = {A computable measure on nonclassicality for light},
journal = {Phys. Rev. Lett.},
year = {2005},
volume = {94},
pages = {173602},
abstract = {We propose the entanglement potential (EP) as a measure of
nonclassicality for quantum states of a single-mode electromagnetic field.
It is the amount of two-mode entanglement that can be generated from the
field using linear optics, auxiliary classical states, and ideal
photodetectors. The EP detects nonclassicality, has a direct physical
interpretation, and can be computed efficiently. These three properties
together make it stand out from previously proposed nonclassicality
measures. We derive closed expressions for the EP of important classes of
states and analyze as an example of the degradation of nonclassicality in
lossy channels.}
month = {May}
}
@Article{KoniorcyzkRB05,
author = {M. Koniorczyk and P. Rapcan and V. Buzek},
title = {Direct versus measurement-assisted bipartite entanglement in m
ultiqubit systems and their dynamical generation in spin systems},
journal = {Phys. Rev. A},
year = {2005},
volume = {72},
number = {2},
pages = {022321},
month = {August},
abstract = {
We consider multiqubit systems and relate quantitatively the problems
of generating cluster states with high values of concurrence of
assistance, and of generating states with maximal bipartite
entanglement. We prove an upper bound for the concurrence of
assistance. We consider dynamics of spin-1/2 systems that model
qubits, with different couplings and possible presence of magnetic
field, to investigate the appearance of the discussed entanglement
properties. We find that states with maximal bipartite entanglement
can be generated by an isotropic XY Hamiltonian, and their generation
can be controlled by the initial state of one of the spins. The same
Hamiltonian is capable of creating states with high concurrence of
assistance from a suitably chosen initial state. We show that the
production of graph states using the Ising Hamiltonian is controllable
via a single-qubit rotation of one spin-1/2 subsystem in the initial
multiqubit state. We show that the property of Ising dynamics to
convert a product-state basis into a special maximally entangled basis
is temporally enhanced by the application of a suitable magnetic
field. Similar basis transformations are found to be feasible in the
case of isotropic XY couplings with a magnetic field.},
URL = {http://link.aps.org/abstract/PRA/v72/e022321}
}
@Article{GabrisA05,
author = {A. G\'abris and G. S. Agarwal},
title = {Vacuum-induced Stark shifts for quantum logic using
a collective system in a high-quality dispersive
cavity},
journal = {Phys. Rev. A},
year = {2005},
volume = {71},
pages = {052316},
month = {May},
abstract = {
A collective system of atoms in a high-quality cavity can be described
by a nonlinear interaction which arises due to the Lamb shift of the
energy levels due to the cavity vacuum [Agarwal et al., Phys. Rev. A
56, 2249 (1997)]. We show how this collective interaction can be used
to perform quantum logic. In particular we produce schemes to realize
controlled-NOT gates not only for two-qubit but also for three-qubit
systems. We also discuss realizations of Toffoli gates. Our effective
Hamiltonian is also realized in other systems such as trapped ions or
magnetic molecules.
},
URL= {http://dx.doi.org/10.1103/PhysRevA.71.052316}
}
@Article{KoniorczykB05,
author = {M. Koniorczyk and V. Buzek},
title = {Nonmaximally entangled bases and their application in entanglement purification via swapping},
journal = {Phys. Rev. A},
year = {2005},
volume = {71},
pages = {032331},
month = {March},
abstract = {
Four basis vectors of the Hilbert space of two qubits have the
property that if three of them are product states, then the fourth one
has to be a product state as well. We address the following situation:
Consider a set of orthogonal vectors, each exhibiting a certain degree
of entanglement. What is the bound on entanglement of the rest of the
basis vectors to form a complete orthonormal basis? Specifically, we
present an orthonormal basis, the Xi basis in the Hilbert space of two
qubits, with one product state and three equally entangled states. The
maximum of the so available entanglement is quantified. A
close-to-optimal protocol is presented for entanglement purification
via entanglement swapping of two-qubit states. It is based on a
suitably chosen nonmaximally entangled basis and carried out in a
single step without any ancillas. A similar application of the Xi
basis is examined. In this latter case, all the involved entangled
states have different and nonorthogonal Schmidt decompositions and,
except for some possibly resulting states, none of them are maximally
entangled. Entanglement of single pair purification is not conserved
on average in this case.
},
URL= {http://dx.doi.org/10.1103/PhysRevA.71.032331}
}
@ARTICLE{KarpatiKA04,
author = {Karpati, A. and Kis, Z. and Adam, P.},
title = {Engineering mixed states in a degenerate four-state
system},
journal = {Phys. Rev. Lett.},
year = {2004},
volume = {93},
pages = {193003},
abstract = {A method is proposed for preparing any pure and wide
class of mixed quantum states in the decoherence-free ground-state
subspace of a degenerate multilevel lambda system. The scheme is a
combination of optical pumping and a series of coherent excitation
processes, and for a given pulse sequence the same final state is
obtained regardless of the initial state of the system. The method
is robust with respect to the fluctuation of the pulse areas, as in
adiabatic methods; however, the field amplitude can be adjusted in
a larger range.}
}
@article{HenkelNDF04,
author = {C. Henkel and M. Nest and P. Domokos and R. Folman},
title = {Optical discrimination between spatial decoherence and
thermalization of a massive object},
journal = {Phys. Rev. A},
year = {2004},
month = {August},
volume = {70},
number = {2},
pages = {023810-1-10},
abstract = {
We propose an optical ring interferometer to observe environment-induced
spatial decoherence of massive objects. The object is held in a harmonic
trap and scatters light between degenerate modes of a ring cavity. The
output signal of the interferometer permits to monitor the spatial width
of the object's wave function. It shows oscillations that arise from
coherences between energy eigenstates and that reveal the difference
between pure spatial decoherence and that coinciding with energy transfer
and heating. Our method is designed to work with a wide variety of masses,
ranging from the atomic scale to nanofabricated structures. We give a
thorough discussion of its experimental feasibility.}
}
@article{AsbothPH04,
author = {J. K. Asbóth and Peter Domokos and Helmut Ritsch},
title = {Correlated motion of two atoms trapped in a single-mode
cavity field},
journal = {Phys. Rev. A},
year = {2004},
month = {July},
volume = {70},
number = {1},
pages = {013414--3002},
abstract = {
We study the motion of two atoms trapped at distant positions in the
field of a driven standing-wave high-Q optical resonator. Even without
any direct atom-atom interaction the atoms are coupled through their
position dependent influence on the intracavity field. For
sufficiently good trapping and low cavity losses the atomic motion
becomes significantly correlated and the two particles oscillate in
their wells preferentially with a 90relative phase shift. The onset of
correlations seriously limits cavity cooling efficiency, raising the
achievable temperature to the Doppler limit. The physical origin of
the correlation can be traced back to a cavity mediated crossfriction,
i.e., a friction force on one particle depending on the velocity of
the second particle. Choosing appropriate operating conditions allows
for engineering these long range correlations. In addition this
cross-friction effect can provide a basis for sympathetic cooling of
distant trapped clouds.}
}
@Article{AsbothAKJ04,
author = {J.K. Asbóth and P. Adam and M. Koniorczyk and J. Janszky},
title = {Coherent-state qubits: entanglement and decoherence},
journal = {Eur. Phys. J. D},
year = {2004},
volume = {30},
number = {3},
pages = {403-410},
month = {September},
abstract= {
Arbitrary superpositions of any two optical coherent states are
investigated as realizations of qubits for quantum information
processing. Decoherence of these coherent-state qubits is described in
detail, and visualized using a suitable adaptive Bloch-sphere. The
entanglement that can be created by a beam splitter from these states
is quantified, and its decoherence behavior is analyzed.},
URL= {http://www.edpsciences.org/articles/epjd/abs/2004/09/d04024/d0
4024.html}
}
@Article{GabrisKAJ04,
author = {A. Gábris and P. Adam and M. Koniorczyk and and J. Janszky},
title = {Distinguishing Schrödinger cats in a lossy environment},
journal = {J. Opt. B: Quantum Semiclass. Opt. },
year = {2004},
volume = {6},
number = {3},
pages = {S84-S89},
month = {March},
abstract = {Optical Schrödinger cat states - that is, even and odd
coherent states - are considered as possible candidates for forming a
computational basis for a coherent state qubit. The distinguishability
of the two originally orthogonal states after experiencing loss is
quantified in terms of quantum relative entropy. This is a physically
instructive quantity related to probabilities of faults in identifying
the state. This distinguishability is important for classical
communication and for the problem of reading out the result of a
quantum computation by a lossy device. It is shown that the
distinguishability can significantly increase if the environment is
prepared in an appropriately chosen squeezed state.},
URL = {http://stacks.iop.org/1464-4266/6/S84}
}
@ARTICLE{DomokosVR04,
author = {Domokos, P. and Vukics, A. and Ritsch, H.},
title = {Anomalous Doppler-effect and polariton-mediated
cooling of two-level atoms},
journal = {Phys. Rev. Lett.},
year = {2004},
volume = {92},
number = {10},
pages = {103601},
abstract = {We consider an atom moving in a near resonant laser
field with its dipole strongly coupled to a resonator field mode.
As compared to the standard Doppler shift, we find a substantially
different and counterintuitive linear velocity dependence of the
light scattering properties. The mechanical force of the laser
field exhibits strong velocity selectivity at a polariton
resonance, which gives rise to an enhanced friction force and
Doppler cooling even in the directions perpendicular to the
resonator axis. This effect allows for sub-Doppler cooling of atoms
even with a nondegenerate ground state.}
}
@ARTICLE{VukicsDR04,
author = {Vukics, A. and Domokos, P. and Ritsch, H.},
title = {Multidimensional and interference effects in atom
trapping by a cavity field},
journal = {J. Opt. B: Quantum Semiclass. Opt.},
year = {2004},
volume = {6},
number = {2},
pages = {143-153},
abstract = {We study the trapping of a driven two-level atom in a
strongly coupled single-mode cavity field. The cavity can
significantly enhance the cooling in the direction perpendicular to
the cavity axis and thus the standard Doppler-cooling scheme
together with a transverse high-finesse resonator yields long
trapping times up to the range of seconds. By the addition of a
weak cavity pump, trapping can be achieved in the direction of the
cavity axis as well. The system is sensitive to the relative phase
of the atomic and cavity pumps due to the interference of the
fields injected and scattered into the cavity mode. Variation of
the phase difference leads to a switching between two possible trap
positions along the cavity axis.}
}
@ARTICLE{KisP04,
author = {Kis, Z. and Paspalakis, E.},
title = {Arbitrary rotation and entanglement of flux SQUID
qubits},
journal = {Phys. Rev. B},
year = {2004},
volume = {69},
number = {2},
pages = {024510},
abstract = {We propose an approach for the arbitrary rotation of a
three-level superconducting quantum interference device (SQUID)
qubit and describe a strategy for the creation of coherence
transfer and entangled states between two three-level SQUID qubits.
The former is succeeded by exploring the coupled-uncoupled states
of the system when irradiated with two microwave pulses, and the
latter is succeeded by placing the SQUID qubits into a microwave
cavity and used adiabatic passage methods for their manipulation.}
}
@ARTICLE{KisP03,
author = {Kis, Z. and Paspalakis, E.},
title = {Enhancing nonlinear frequency conversion using
spatially dependent coherence},
journal = {Phys. Rev. A},
year = {2003},
volume = {68},
number = {4},
pages = {043817},
abstract = {We consider pulse propagation in a Lambda-type medium
with spatially dependent coherence. It has been shown in previous
works that it is impossible to get complete nonlinear energy
conversion between an injected pulse and a generated pulse for
homogenous coherence distribution. The aim of our work is to
achieve unity conversion efficiency. We show by analytic
considerations and numerical simulations that this can be achieved
only if the propagation satisfies the conditions of adiabaticity in
the local frame on the position domain. We also derive an exact
analytic model for pulse propagation in our A-type medium, which is
valid even if adiabaticity is not satisfied.}
}
@ARTICLE{VitanovKS03,
author = {Vitanov, N. V. and Kis, Z. and Shore, B. W.},
title = {Coherent excitation of a degenerate two-level system
by an elliptically polarized laser pulse},
journal = {Phys. Rev. A},
year = {2003},
volume = {68},
number = {6},
pages = {063414},
abstract = {The elaborate linkage pattern of the interaction
Hamiltonian descriptive of pulsed laser interaction of elliptically
polarized light with a degenerate two-level system can, for
coherent excitation, be reduced to sets of independent pairs of
coupled two-state equations by means of the Morris-Shore
transformation [Phys. Rev. A 27, 906 (1983)]. By extending the
earlier defining work, which dealt only with time-independent
interactions, to consider various pulse shapes, one can obtain
exact analytic solutions to various multilevel linkages. We use
these to find the conditions on the interaction parameters (e.g.,
the ellipticity) leading to various population transfer schemes,
for example, to achieve either population inversion or orientation.
We illustrate these with the M and W linkages amongst magnetic
sublevels of J=1 or J=2 excited by elliptically polarized light.}
}
@ARTICLE{AdamKGJ03,
author = {Adam, P. and Karpati, A. and Gawlik, W. and Janszky,
J.},
title = {Competitive stochastic noises an coherently driven
two-level atoms and quantum interference},
journal = {J. Opt. B-Quantum Semicl. Opt.},
year = {2003},
volume = {5},
pages = {S221-S227},
abstract = {A system of coherently driven two-level atoms is
analysed in the presence of two independent stochastic
perturbations: one due to collisions and a second due to phase
fluctuations of the driving field. The behaviour of the quantum
interference induced by the collisional noise is considered in
detail. The quantum-trajectory method is utilized to reveal the
phase correlations between the dressed states involved in the
interfering transition channels. It is shown that the quantum
interference induced by the collisional noise is remarkably robust
against phase noise. This effect is due to the fact that the phase
noise, similarly to collisions, stabilizes the phase difference
between the dressed states.
}
}
@ARTICLE{KoniorczykB03,
author = {Koniorczyk, M. and Buzek, V.},
title = {Simulation of exponential decay on simple quantum
circuits: a case study},
journal = {J. Opt. B-Quantum Semicl. Opt.},
year = {2003},
volume = {5},
pages = {S329-S332},
abstract = {One of potential applications of quantum processors
should be a simulation of dynamics of quantum systems. In this
paper we analyse whether it is possible to simulate a paradigmatic
model of an exponential decay of a two-level system using a
programmable quantum gate array. That is, we would like to simulate
the decay of a two-level system in such a way that the parameters
of the decay itself are encoded in the state of the ancilla that
serves as a program for the programmable gate array. We show that
it is impossible to simulate the exponential decay precisely with
the finite-dimensional programmable gate array. On the other hand,
we present a very simple model of a Markovian decay process that
can be efficiently simulated on a simple programmable gate array.
We compare this Markovian process with the exponential decay.}
}
@ARTICLE{DomokosR03,
author = {Domokos, P. and Ritsch, H.},
title = {Mechanical effects of light in optical resonators},
journal = {J. Opt. Soc. Am. B-Opt. Phys.},
year = {2003},
volume = {20},
pages = {1098-1130},
abstract = {We review the modifications and implications of the
effect of light forces on atoms when the field is enclosed in an
optical resonator of high finesse. The systems considered range
from a single atom strongly coupled to a single mode of a high-Q
microcavity to a large ensemble of atoms in a highly degenerate
quasi-confocal resonator. We set up general models that allow us to
obtain analytic expressions for the optical potential, friction,
and diffusion. In the bad-cavity limit the modified cooling
properties can be attributed to the spectral modifications of light
absorption and spontaneous emission in a form of generalized and
enhanced Doppler cooling. For the strong coupling regime in a good
cavity, we identify the dynamical coupling between the light field
intensity and the atomic motion as the central mechanism underlying
the cavityinduced cooling. The dynamical cavity cooling, which
does not rely on spontaneous emission, can be enhanced by multimode
cavity geometries because of the effect of coherent photon
redistribution between different modes. The model is then
generalized to include several distinct frequencies to account for
more general trap geometries. Finally we show that the
field-induced buildup of correlations between the motion of
different particles plays a central role in the scaling behavior of
the system. Depending on the geometry and parameters, its effect
ranges from strong destructive interference, slowing down the
cooling process, to self- organized crystallization, implying
atomic self-trapping and faster cooling to lower temperatures by
cooperative coherent scattering. (C) 2003 Optical Society of
America.
}
}
@ARTICLE{HorakKHFSDH03,
author = {Horak, P. and Klappauf, B. G. and Haase, A. and
Folman, R. and Schmiedmayer, J. and Domokos, P. and Hinds, E. A.},
title = {Possibility of single-atom detection on a chip},
journal = {Phys. Rev. A},
year = {2003},
volume = {67},
pages = {art. no.-043806},
abstract = {We investigate the optical detection of single atoms
held in a microscopic atom trap close to a surface. Laser light is
guided by optical fibers or optical microstructures via the atom to
a photodetector. Our results suggest that with present-day
technology microcavities can be built around the atom with
sufficiently high finesse to permit unambiguous detection of a
single atom in the trap with 10 mus of integration. We compare
resonant and nonresonant detection schemes and discuss the
requirements for detecting an atom without causing it to undergo
spontaneous emission.
}
}
@ARTICLE{JanszkyAGVKK03,
author = {Janszky, J. and J.K. Asbóth, and Gábris, A. and Vukics,
A. and Koniorczyk, M. and Kobayashi, T.},
title = {Two-mode Schrodinger cats, entanglement and
teleportation},
journal = {Fortschritte Phys.-Prog. Phys.},
year = {2003},
volume = {51},
pages = {157-171},
abstract = {Two-mode Schrodinger cats consisting of two and four
coherentstate terms are considered. It is shown that they are
closely related to the quadrature entangled EPR pair. The
properties of their wave functions are investigated from their
aspects of entanglement. It is shown that at certain parameters the
entangled properties of the two-mode Schrodinger cats allow for
good teleportation fidelity. A theoretical generalization to the
teleportation of two qubits is also discussed.
}
}
@ARTICLE{KarpatiAGLJ03,
author = {Karpati, A. and Adam, P. and Gawlik, W. and
Lobodzinski, B. and Janszky, J.},
title = {Quantum trajectory approach to stochastically-induced
quantum interference},
journal = {Fortschritte Phys.-Prog. Phys.},
year = {2003},
volume = {51},
pages = {179-185},
abstract = {Stochastic perturbation of two-level atoms strongly
driven by a coherent light field is analyzed by the quantum
trajectory method. Narrow resonances as hole burning and dispersive
Fanolike profile occur in the spectra in the regime where the
noise dominates the Rabi oscillations. It is shown that in this
case the stochastic noise can unexpectedly create phase correlation
between the neighboring atomic dressed states. This phase
correlation is responsible for quantum interference between the
related transitions resulting in anomalous modifications of the
resonance fluorescence spectra.
}
}
@ARTICLE{HorakDR03,
author = {Horak, P. and Domokos, P. and Ritsch, H.},
title = {Giant Lamb shift of atoms near lossy multimod optical
microwaveguides},
journal = {Europhys. Lett.},
year = {2003},
volume = {61},
pages = {459-465},
abstract = {Atoms coupled to optical fields strongly confined in
two spatial dimensions, as in solid-state microstructures, can
experience large Lamb shifts due to a spectrally strongly
asymmetric mode density. We use the generic example of a quasi
one-dimensional waveguide structure driven close to cutoff
frequency of a new transverse branch of propagating modes. W
analytically find strong shifts of the atomic resonance frequency
due to the modified vacuum, which can be an order of magnitude
larger than the atomic linewidth. At the same time one gets
significantly enhanced scattering of the guided light by the atom,
which could be used as a tool to investigate these effects or to
build non-destructive single-atom detectors.}
}
@ARTICLE{DomokosR02,
author = {Domokos, P. and Ritsch, H.},
title = {Collective cooling and self-organization of atoms in a
cavity},
journal = {Phys. Rev. Lett.},
year = {2002},
volume = {89},
pages = {art. no.-253003},
abstract = {We theoretically investigate the correlated dynamics
of N coherently driven atoms coupled to a standing-wave cavity
mode. For red detuning between the driving field and the cavity as
well as the atomic resonance frequencies, we predict a light force
induced self-organization of the atoms into one of two possible
regular patterns, which maximize the cooperative scattering of
light into the cavity field. Kinetic energy is extracted from the
atoms by superradiant light scattering to reach a final kinetic
energy related to the cavity linewidth. The self-organization
starts only above a threshold of the pump strength and atom number.
We find a quadratic dependence of the cavity mode intensity on the
atom number, which demonstrates the cooperative effect.
}
}
@ARTICLE{DomokosSR02,
author = {Domokos, P. and Salzburger, T. and Ritsch, H.},
title = {Dissipative motion of an atom with transverse coherent
driving in a cavity with many degenerate modes},
journal = {Phys. Rev. A},
year = {2002},
volume = {66},
pages = {art. no.-043406},
abstract = {We study the cavity-induced cooling of the
center-of-mass motion of a transversally coherently pumped atom
moving along the axis of a high-Q multimode cavity. Including
spontaneous emission and quantum fluctuations of the cavity field,
we analytically calculate the linear friction and the diffusion
coefficients. Efficient cavity-induced motional damping leads to
steady-state temperatures well below the Doppler limit and lower
than for an equivalent setup with direct cavity field pumping. The
cooling process is strongly enhanced in the case of a multimode
field, yielding a significantly lower temperature and a small
number of spontaneous emissions per cooling time, which can even
drop below 1.
}
}
@ARTICLE{SalzburgerDR02,
author = {Salzburger, T. and Domokos, P. and Ritsch, H.},
title = {Enhanced atom capturing in a high-Q cavity by help of
several transverse modes},
journal = {Opt. Express},
year = {2002},
volume = {10},
pages = {1204-1214},
abstract = {We predict a strong enhancement of the capture rate
and the friction force for atoms crossing a driven high-Q cavity
field if several near degenerate cavity modes are simultaneously
coupled to the atom. In contrast to the case of a single TEM00
mode, circular orbits are not stable and damping of the angular and
radial motion occurs. Depending on the chosen atom-field detuning
the atoms phase lock the cavity modes to create a localized field
minimum or maximum at their current positions. This corresponds to
a local potential minimum which the atom drags along with its
motion. The stimulated photon redistribution between the modes then
creates a large friction force. The effect is further enhanced if
the atom is directly driven by a coherent field from the side.
Several atoms in the field interact via the cavity modes, which
leads to a strongly correlated motion. (C) 2002 Optical Society of
America.}
}
@ARTICLE{VukicsJK02,
author = {Vukics, A. and Janszky, J. and Kobayashi, T.},
title = {Nonideal teleportation in coherent-state basis},
journal = {Phys. Rev. A},
year = {2002},
volume = {66},
pages = {art. no.-023809},
abstract = {A coherent representation has been developed for
entanglement and measurement, which is an elegant approach to
continuous variable quantum teleportation. In the present paper
this frame is used to deal with nonideal elements of the
experimental situation, such as inefficiencies of the Bell
measurement, loss, and thermal noise in the nonlinear crystal used
for producing entangled pairs. A measure of fidelity is introduced
for characterizing the quality of nonideal schemes.
}
}
@ARTICLE{KarpatiAGLJ02,
author = {Karpati, A. and Adam, P. and Gawlik, W. and
Lobodzinski, B. and Janszky, J.},
title = {Quantum-trajectory approach to stochastically induced
quantuminterference effects in coherently driven two-level atoms},
journal = {Phys. Rev. A},
year = {2002},
volume = {66},
pages = {art. no.-023821},
abstract = {Stochastic perturbation of two-level atoms strongly
driven by a coherent light field is analyzed by the
quantum-trajectory method. A method is developed for calculating
the resonance fluorescence spectra from numerical simulations. It
is shown that in the case of dominant incoherent perturbation, the
stochastic noise can unexpectedly create phase correlation between
the neighboring atomic dressed states. This phase correlation is
responsible for quantum interference between the related
transitions resulting in anomalous modifications of the resonance
fluorescence spectra.
}
}
@ARTICLE{JanszkyGKVA02,
author = {Janszky, J. and Gábris, A. and Koniorczyk, M. and
Vukics, A. and J.K. Asbóth},
title = {One-complex-plane representation: a coherent-state
description of entanglement and teleportation},
journal = {J. Opt. B-Quantum Semicl. Opt.},
year = {2002},
volume = {4},
pages = {S213-S217},
abstract = {It is shown that any state of two modes of the
electromagnetic field (or any other bipartite bosonic system) can
be expressed as a coherent superposition of conjugate
coherent-state pairs. This representation has a deep connection
with both the twomode squeezing operator and a maximally
entangled basis. A description of continuous variable quantum
teleportation is presented, as an example of the application of
this method.}
}
@ARTICLE{JaniKNLBLC02,
author = {Jani, P. and Koniorczyk, M. and Nagy, A. and Lipp, Z.
and Bartal, B. and Laszlo, A. and Czitrovszky, A.},
title = {Probability distribution of scattered intensities},
journal = {J. Aerosol. Sci.},
year = {2002},
volume = {33},
pages = {697-704},
abstract = {The probability distribution of scattered light
intensity is derived when both the size and the number of
scattering aerosol particles are random variables. When light is
scattered from an ensemble of aerosol particles, the scattered
intensity is a random variable itself. Analytical derivation is
found for the distribution of scattered intensities. It is shown
that in a wide range of experimental conditions the scattered
intensity follows Gaussian statistics. For a given sort of aerosols
the ratio of the mean value to the standard deviation is shown to
be dependent only on the mean number of particles present in the
measurement volume. Monte-Carlo simulations and experiments were
carried out to prove the expectations of the theory. (C) 2002
Elsevier Science Ltd. All rights reserved.
}
}
@ARTICLE{DomokosHR02,
author = {Domokos, P. and Horak, P. and Ritsch, H.},
title = {Quantum description of light-pulse scattering on a
single atom in waveguides},
journal = {Phys. Rev. A},
year = {2002},
volume = {65},
pages = {art. no.-033832},
abstract = {We present a time-dependent quantum calculation of the
scattering of a few-photon pulse on a single atom. The photon wave
packet is assumed to propagate in a transversely strongly confined
geometry, which ensures strong atom-light coupling and allows a
quasi-one-dimensional treatment. The amplitude and phase of the
transmitted, reflected, and transversely scattered part of the wave
packet strongly depend on the pulse length (bandwidth) and energy.
For a transverse mode size of the order of lambda(2), we find
nonlinear behavior for a few photons already, or even for a single
photon. In a second step we study the collision of two such wave
packets at the atomic site and find striking differences between
the Fock state and coherent state wave packets of the same photon
number.
}
}
@ARTICLE{DomokosHR01,
author = {Domokos, P. and Horak, P. and Ritsch, H.},
title = {Semiclassical theory of cavity-assisted light forces
on atoms and applications},
journal = {Fortschritte Phys.-Prog. Phys.},
year = {2001},
volume = {49},
pages = {935-940},
abstract = {We present a semiclassical theory that can describe
the centreof-mass motion of a neutral atom in a strongly coupled
cavity field. We show that a cavity-assisted cooling mechanism can
lead to efficient loading of an atom into a wavelength size optical
microtrap.
}
}
@ARTICLE{JanszkyGKVA01,
author = {Janszky, J. and Gábris, A. and Koniorczyk, M. and
Vukics, A. and Adam, P.},
title = {Coherent-state approach to entanglement and
teleportation},
journal = {Fortschritte Phys.-Prog. Phys.},
year = {2001},
volume = {49},
pages = {993-1000},
abstract = {Two-mode oscillator quantum states are described via
coherent state superpositions. The one-complex-plane coherent-state
representation is introduced as a generalization of low-
dimensional coherent-state representations of single mode fields.
Application to two-mode squeezed states is emphasized, because of
their entangled nature and applicability for quantum communication.
Continuous variable quantum teleportation is treated in this
framework.
}
}
@ARTICLE{KuruczKJ01,
author = {Kurucz, Z. and Koniorczyk, M. and Janszky, J.},
title = {Teleportation with partially entangled states},
journal = {Fortschritte Phys.-Prog. Phys.},
year = {2001},
volume = {49},
pages = {1019-1025},
abstract = {The relations of antilinear maps, bipartite states and
quantum channels is summarized. Antilinear maps are applied to
describe bipartite states and entanglement. Teleportation is
treated in this general formalism with an emphasis on conditional
schemes applying partially entangled pure states. It is shown that
in such schemes the entangled state shared by the parties, and
those measured by the sender should ''match'' each other.}
}
@ARTICLE{SzaboAKJ01,
author = {Szabo, S. and Adam, P. and Karpati, A. and Janszky,
J.},
title = {Phase optimized light in complex optical systems},
journal = {Fortschritte Phys.-Prog. Phys.},
year = {2001},
volume = {49},
pages = {1109-1116},
abstract = {Evolution of phase optimized light in complex two-mode
optical systems of quadratic Hamiltonian is analyzed. It is shown
that amplification of phase optimized light, and enhancement of
phase squeezing preserving the phase optimized property can be
realized in these systems with an appropriate set of parameters.
}
}
@ARTICLE{KoniorczykKJ01,
author = {Koniorczyk, M. and Kiss, T. and Janszky, J.},
title = {Teleportation: from probability distributions to
quantum states},
journal = {J. Phys. A-Math. Gen.},
year = {2001},
volume = {34},
pages = {6949-6955},
abstract = {The role of the off-diagonal density-matrix elements
of the entangled pair is investigated in the quantum teleportation
of a qubit. The dependence between these elements and the off-
diagonal elements of the teleported density matrix is shown to be
linear. In this way ideal quantum teleportation is related to a
completely classical communication protocol: the one-time pad
cypher. The latter can be regarded as the classical counterpart of
Bennett's quantum-teleportation. scheme. The quantum-to-classical
transition is demonstrated by a gedankenexperiment.
}
}
@ARTICLE{KoniorczykBJ01,
author = {Koniorczyk, M. and Buzek, V. and Janszky, J.},
title = {Wigner-function description of quantum teleportation
in arbitrary dimensions and a continuous limit},
journal = {Phys. Rev. A},
year = {2001},
volume = {6403},
pages = {art. no.-034301},
abstract = {We present a unified approach to quantum teleportation
in arbitrary dimensions based on the Wigner-function formalism.
This approach provides us with a clear picture of all manipulations
performed in the teleportation protocol. In addition within the
framework of the Wigner-function formalism all the imperfections of
the manipulations can be easily taken into account.
}
}
@ARTICLE{JanszkyKG01,
author = {Janszky, J. and Koniorczyk, M. and Gábris, A.},
title = {One-complex-plane representation approach to
continuous variable quantum teleportation},
journal = {Phys. Rev. A},
year = {2001},
volume = {6403},
pages = {art. no.-034302},
abstract = {We formulate continuous variable quantum teleportation
on a coherent-state basis. We present low-dimensional coherent
state representation of the quadrature Bell states. This approach
turns out to be suitable for investigating the teleportation
process, yielding a simple direct description.
}
}
@ARTICLE{Janszky01,
author = {Janszky, J.},
title = {In memoriam Imre Tarjan},
journal = {Acta Phys. Hung. New Ser.-Heavy Ion Phys.},
year = {2001},
volume = {13},
pages = {207-209},
abstract = {}
}
@ARTICLE{DomokosHR01b,
author = {Domokos, P. and Horak, P. and Ritsch, H.},
title = {Semiclassical theory of cavity-assisted atom cooling},
journal = {J. Phys. B-At. Mol. Opt. Phys.},
year = {2001},
volume = {34},
pages = {187-198},
abstract = {We present a systematic semiclassical model for the
simulation of the dynamics of a single two-level atom strongly
coupled to a driven high-finesse optical cavity. From the
Fokker-Planck equation of the combined atom-field Wigner function
we derive stochastic differential equations for the atomic motion
and the cavity field. The corresponding noise sources exhibit
strong correlations between the atomic momentum fluctuations and
the noise in the phase quadrature of the cavity field. The model
provides an effective tool to investigate localization effects as
well as cooling and trapping times. In addition,we can continuously
study the transition from a few-photon quantum field to the
classical limit of a large coherent field amplitude.
}
}
@ARTICLE{DomokosR01,
author = {Domokos, P. and Ritsch, H.},
title = {Efficient loading and cooling in a dynamic optical
evanescentwave microtrap},
journal = {Europhys. Lett.},
year = {2001},
volume = {54},
pages = {306-312},
abstract = {We calculate the loading efficiency and cooling rates
in a bichromatic optical microtrap, where the optical potentials
are generated by evanescent waves of cavity fields at a dielectric-
vacuum interface. The cavity modi ed nonconservative dynamic light
forces lead to efficient loading of the atoms as well as cooling
without the need for spontaneous emission. Steady-state
temperatures well below the trap depth, reaching the motional
quantum regime, yield very long capturing times for a neutral atom.
}
}
@ARTICLE{DomokosKJ01,
author = {Domokos, P. and Kiss, T. and Janszky, J.},
title = {Selecting molecules in the vibrational and rotational
ground state by deflection},
journal = {Eur. Phys. J. D},
year = {2001},
volume = {14},
pages = {49-53},
abstract = {A beam of diatomic molecules scattered off a standing
wave laser mode splits according to the rovibrational quantum state
of the molecules. Our numerical calculation shows that single state
resolution can be achieved by properly tuned, monochromatic light.
The proposed scheme allows for selecting non vibrating and
non-rotating molecules from a thermal beam, implementing a laser
Maxwell's demon to prepare a rovibrationally cold molecular
ensemble.
}
}
@ARTICLE{DomokosGR00,
author = {Domokos, P. and Gangl, M. and Ritsch, H.},
title = {Single-atom detection in high-Q multimode cavities},
journal = {Opt. Commun.},
year = {2000},
volume = {185},
pages = {115-123},
abstract = {We propose a new method for detecting and monitoring
the motion of a single atom in high-Q optical resonators based on
the position sensitive dispersive coupling of different field
modes. Using sufficient atom-field detuning the irreversible
evolution of the internal state and external motion of the atom can
be kept small still allowing for a fast and reliable detection. As
an implementation we discuss the case of two counterpropagating
modes in a microscopic ring resonator with spatially localized
output coupler. The analytical estimates yielding 100\% signal
contrast for suitable parameters are then confirmed by numerical
solution of the time-dependent equations for the coupled
atom-cavity dynamics. (C) 2000 Elsevier Science B.V. All rights
reserved.
}
}
@ARTICLE{KarpatiAJBS00,
author = {Karpati, A. and Adam, P. and Janszky, J. and
Bertolotti, M. and Sibilia, C.},
title = {Nonclassical light in complex optical systems},
journal = {J. Opt. B-Quantum Semicl. Opt.},
year = {2000},
volume = {2},
pages = {133-139},
abstract = {A general method is developed for analysing the
evolution of nonclassical light in complex two-mode optical systems
where linear and nonlinear processes with quadratic Hamiltonians
can take place simultaneously or successively. Analytic expressions
are derived for the output Wigner function and the output photon
number distribution for a general coherent-state superposition
input that can approximate any quantum state of light with a high
degree of accuracy. As an example, the evolution of amplitude
squeezed light is analysed in a nonlinear coupler with degenerate
and nondegenerate parametric amplification. it is shown that
all-optical switching can be realized in this system.
}
}
@ARTICLE{KoniorczykKGJ00,
author = {Koniorczyk, M. and Kurucz, Z. and Gábris, A. and
Janszky, J.},
title = {General optical state truncation and its
teleportation},
journal = {Phys. Rev. A},
year = {2000},
volume = {6201},
pages = {art. no.-013802},
abstract = {A setup is proposed in which the number-state
expansion of a one-mode traveling-wave optical field is truncated
so as to Leave its vacuum, one-, and two-photon components. The
process is a realization of quantum teleportation on a three-state
basis. The possibility of generalization to the first n components
is also considered.
}
}
@ARTICLE{DomokosHLRHPD00,
author = {Domokos, P. and Hare, J. and Lefevre, V. and Raimond,
J. M. and Haroche, S. and Protsenko, I. and Davidovich, L.},
title = {Quantum theory of microlasers in the
close-to-threshold regime},
journal = {Laser Phys.},
year = {2000},
volume = {10},
pages = {42-47},
abstract = {We present a new analytical method to solve the basic
Heisenberg-Langevin equations of the standard quantum model of a
single-mode laser. The method is valid for describing microlasers
operating in the strong coupling regime (cavity QED lasers). These
lasers can exhibit fascinating properties: for example, the very
notion of threshold may break down. Owing to the analytic solutions
of the new model, the laser operation in the close-to-threshold
regime can be studied, which leads us to a natural characterization
of the threshold's behavior.}
}
@ARTICLE{KisKJAWV00,
author = {Kis, Z. and Kiss, T. and Janszky, J. and Adam, P. and
Wallentowitz, S. and Vogel, W.},
title = {Detection of nonclassical oscillations in phase space
by cascaded optical homodyning},
journal = {Laser Phys.},
year = {2000},
volume = {10},
pages = {90-92},
abstract = {We discuss a recently proposed scheme for the
reconstruction of the quantum state of a one-mode traveling light
wave. In the cascaded homodyning scheme the balanced and unbalanced
principles of homodyning are combined. We present here a derivation
of the universal sampling function by inverting the Radon
transformation occurring in the second stage of the setup. The
sampling function possesses a simple structure, which is
independent of the location of the phase-space point. This latter
property makes it a promising tool for detecting nonclassical
oscillations in quasiprobability functions.}
}
@ARTICLE{AdamKJSL00,
author = {Adam, P. and Karpati, A. and Janszky, J. and Szabo, S.
and Lugosi, E.},
title = {Relations between input and output quantum states of
integrated optical systems},
journal = {Laser Phys.},
year = {2000},
volume = {10},
pages = {127-132},
abstract = {Relations between the input and the output
quasiprobability distribution functions, Glauber's R-functions, and
photon number representations of the density operator are found for
a general optical four-port calculated.
}
}
@ARTICLE{SzaboAJ00,
author = {Szabo, S. and Adam, P. and Janszky, J.},
title = {Phase optimized states via coherent-state
superpositions},
journal = {Laser Phys.},
year = {2000},
volume = {10},
pages = {139-142},
abstract = {It is shown that phase optimized quantum states of the
electromagnetic field can be constructed by continuous and discrete
superpositions of coherent states along the positive real semiaxis
in phase space. Systematic method is developed for finding optimal
coherent-state superpositions.
}
}
@ARTICLE{KoniorczykJK99,
author = {Koniorczyk, M. and Janszky, J. and Kis, Z.},
title = {Three-photon states for quantum teleportation},
journal = {Acta Phys. Slovaca},
year = {1999},
volume = {49},
pages = {707-712},
abstract = {A three-particle generalization of the quantum
teleportation of polarization states is discussed. A possible
nonlinear optical process is discussed, which can lead the required
EPR-states. The Bell-state analysis of our three-photon Bell-states
applying a beam-splitter and polarization analyzers is discussed.
}
}
@ARTICLE{KoniorczykJK99a,
author = {Koniorczyk, M. and Janszky, J. and Kis, Z.},
title = {Photon number teleportation},
journal = {Phys. Lett. A},
year = {1999},
volume = {256},
pages = {334-338},
abstract = {It is shown that a superposition state \Phi]) of one
and two photons can be teleported using an optical teleportation
scheme. A Bell-state analysis for entangled oneand two-photon
states is discussed. A Gedankenexperiment is presented in which the
state \Phi] is teleported with 50\% efficiency. (C) 1999 Elsevier
Science B.V. All rights reserved.
}
}
@ARTICLE{ProtsenkoDLHRD99,
author = {Protsenko, I. and Domokos, P. and Lefevre-Seguin, V.
and Hare, J. and Raimond, J. M. and Davidovich, L.},
title = {Quantum theory of a thresholdless laser},
journal = {Phys. Rev. A},
year = {1999},
volume = {59},
pages = {1667-1682},
abstract = {We develop a quantum theory of a single-mode
thresholdless laser. We start from basic Heisenberg-Langevin
equations of motion for the field and atomic operators, and obtain
an approximate analytical solution to these operator equations. We
compare the predictions of this model for the intensity and power
spectrum of the field to the results of a Monte Carlo numerical
simulation of the original Heisenberg-Langevin equations, and find
them in excellent agreement. We also compare these predictions to
those of a rate-equation model, which takes into account
spontaneous emission. We show that our model gives more reliable
results in the bad cavity limit at high intensities. Based upon
these results, we propose a simple characterization of the
thresholdless behavior. Finally, we apply our model to microsphere
Nd-doped lasers at low temperatures, which are promising devices
for a well-controlled thresholdless operation.
[S1050-2947(99)10502-X].
}
}
@ARTICLE{JanszkyKA98,
author = {Janszky, J. and Kis, Z. and Adam, P.},
title = {Star states},
journal = {Fortschritte Phys.-Prog. Phys.},
year = {1998},
volume = {46},
pages = {829-835},
abstract = {It is shown that the classical and quantum mechanical
description of first and second order nonlinear optical processes
(including squeezing) are equivalent to the effect that in both
cases an initial phase space distribution is transformed in the
same manner. Three-photon states - star states - are generated in
third order nonlinear processes, where the classical and quantum
descriptions give essentially different results. It is pointed out
that the efficiency of the star state in a three photon process is
superior to that of a coherent state with two order of magnitude.
}
}
@ARTICLE{SzaboDAJ98,
author = {Szabo, S. and Domokos, P. and Adam, P. and Janszky,
J.},
title = {Coherent-state representation on an infinitesimal
interval in phase space},
journal = {Phys. Lett. A},
year = {1998},
volume = {241},
pages = {203-206},
abstract = {A coherent-state representation of the Hilbert space
of the harmonic oscillator is presented. The basis set consists of
the coherent states \alpha with real parameter a which are in an
infinitesimal vicinity of zero. (C) 1998 Elsevier Science B.V.}
}
@ARTICLE{KissHL98,
author = {Kiss, T. and Herzog, U. and Leonhardt, U.},
title = {Reply to ''Loss-error compensation in quantum-state
measurements''},
journal = {Phys. Rev. A},
year = {1998},
volume = {57},
pages = {3134-3135},
abstract = {The authors of the preceding Comment [G. M. D'Ariano
and C. Macchiavello, preceding paper, Phys. Rev. A 57, 3131 (1998)]
tried to reestablish a 0.5 efficiency bound for loss compensation
in optical homodyne tomography. In our reply we demonstrate that
neither does such a rigorous bound exist nor is the bound required
for ruling out the state reconstruction of an individual system [G.
M. D'Ariano and H. P. Yuen, Phys. Rev. Lett. 76, 2832 (1996)].
}
}
@ARTICLE{DomokosBRH98,
author = {Domokos, P. and Brune, M. and Raimond, J. M. and
Haroche, S.},
title = {Photon-number-state generation with a single two-level
atom in a cavity: a proposal},
journal = {Eur. Phys. J. D},
year = {1998},
volume = {1},
pages = {1-4},
abstract = {A single two-level atom can be used to prepare an
arbitrary photon number state (Fock state) in a high Q cavity. The
atom undergoes a controlled succession of interactions with two
cavity modes. One of them contains a coherent field. The atom
transfers photons one by one from this field to the initially empty
second mode. The scheme can be extended to prepare a quantum
superposition of the vacuum with a Fock state, a highly
non-classical situation. We discuss the feasibility of the
experiment with our present Rydberg-atom cavity QED set-up.}
}
@ARTICLE{TreussartIRDHLRH98,
author = {Treussart, F. and Ilchenko, V. S. and Roch, J. F. and
Domokos, P. and Hare, J. and Lefevre, V. and Raimond, J. M. and
Haroche, S.},
title = {Whispering gallery mode microlaser at liquid Helium
temperature},
journal = {J. Lumines.},
year = {1998},
volume = {76-7},
pages = {670-673},
abstract = {We report on the realization of neodymium-doped silica
microsphere laser, of diameters in the range 50-100 mu m. Following
very low threshold observed at room temperature (absorbed pump
power of 200 nW), we present the new cryogenic setup operating at
2K. Very high quality factor Q > 3 x 10(8) has been preserved in a
50 mu m diameter microsphere immersed in superfluid Helium.
Preliminary results on lasing at this temperature have also been
obtained as a first step towards a 'thresholdless' regime. (C) 1998
Elsevier Science B.V. All rights reserved.
}
}
@ARTICLE{AdamJDS97,
author = {Adam, P. and Janszky, J. and Domokos, P. and Szabo,
S.},
title = {Preparation of two-mode anticorrelated photon-number
state via atom de Broglie wave deflection},
journal = {J. Mod. Opt.},
year = {1997},
volume = {44},
pages = {2125-2133},
abstract = {It is shown that the deflection of an atom de Broglie
wave at two adjacent cavities containing non-resonant weak fields
can yield a highly entangled quantum state of the atom-field system
in which discernible atomic beams are entangled to internal states
of the atom and to two-mode photon-number states of the fields.
Two-mode anticorrelated entangled photon-number states
characterized by the total photon number can be prepared by the
detection of the atom in given directions of the propagation.}
}
@ARTICLE{PaulTKJ97,
author = {Paul, H. and Torma, P. and Kiss, T. and Jex, I.},
title = {Multiple coincidences and the quantum state
reconstruction problem},
journal = {Phys. Rev. A},
year = {1997},
volume = {56},
pages = {4076-4085},
abstract = {We analyze the recently proposed method [H. Paul et
al., Phys. Rev. Lett. 76, 2464 (1996)] for reconstructing the
quantum state of a light field from multiple coincidences measured
at the outputs of a passive multiport. We show that applying a
large multiport the reconstruction of a pure state becomes possible
using avalanche photodiode-type detectors. The presented
simulations show that the photon chopping scheme is appropriate for
the indirect measurement of the photon statistics of a weak
nonclassical signal. [S1050-2947(97)075070].
}
}
@ARTICLE{DomokosAJZ96,
author = {Domokos, P. and Adam, P. and Janszky, J. and
Zeilinger, A.},
title = {Atom de Broglie wave deflection by a single cavity
mode in the few-photon limit: Quantum prism},
journal = {Phys. Rev. Lett.},
year = {1996},
volume = {77},
pages = {1663-1666},
abstract = {It is shown that the deflection of an atom de Broglie
wave at a nonresonant weak cavity field mode can yield a pure
entangled quantum state in which discernable atomic beams ate
entangled to photon number states of the field and to internal
states of the atom. The proposed experimental scheme is shown to be
applicable for quantum nondemolition measurement of the photon
statistics, and for quantum state engineering and reconstruction
experiments.
}
}
@ARTICLE{AdamSJ96,
author = {Adam, P. and Szabo, S. and Janszky, J.},
title = {Phase optimized states via discrete coherent-state
superpositions},
journal = {Phys. Lett. A},
year = {1996},
volume = {215},
pages = {229-233},
abstract = {It is shown that phase optimized quantum states of the
electromagnetic field can be constructed by superpositions of a
small number of coherent states along the positive real semiaxis in
phase space. A systematic method is developed for finding optimal
coherent-state superpositions.
}
}
@ARTICLE{VinogradovJK96,
author = {Vinogradov, A. V. and Janszky, J. and Kobayashi, T.},
title = {A single-molecule interferometer for measurement of
femtosecond laser pulse duration},
journal = {Opt. Commun.},
year = {1996},
volume = {127},
pages = {223-229},
abstract = {An electronic excitation of a molecule by a sequence
of two femtosecond phase-locked laser pulses is considered. In this
case interference takes place between the vibrational wave packets
induced by each of the subpulses within a single molecule. It is
shown that, due to the dynamical squeezing effect of a molecular
vibrational state, this interference allows one to measure the
duration of a femtosecond laser pulse. This can be achieved
experimentally by measuring the dependence of the integral
fluorescence of the excited molecule on the delay time between the
subpulses. The interference can lead to a sharp peak (or to a dip)
in that dependence, the width of which is equal to the duration of
the laser pulse. It is shown that a finite temperature of the
medium is favourable for such an experiment.
}
}
@ARTICLE{LeonhardtMKRR96,
author = {Leonhardt, U. and Munroe, M. and Kiss, T. and Richter,
T. and Raymer, M. G.},
title = {Sampling of photon statistics and density matrix using
homodyne detection},
journal = {Opt. Commun.},
year = {1996},
volume = {127},
pages = {144-160},
abstract = {The photon statistics and, moreover, the density
matrix (quantum state) of a single light mode can be sampled using
homodyne detection. That is, the density matrix is computed by
averaging a set of sampling functions with respect to the measured
quadrature values. We develop a practical procedure for evaluating
these functions. The algorithm is simple, stable, has small
computer-memory requirements, and is fast enough for real-time data
processing. (Interestingly, our method involves unnormalizable
solutions of the stationary Schrodinger equation. We develop the
annihilation-and-creation formalism for these solutions and derive
their semiclassical approximations.) We quantify the bin width
required to determine the density matrix up to a maximal quantum
number. Finally, we show how the statistical errors of the
reconstructed density matrix can be determined from the measured
data.
}
}
@ARTICLE{SzaboAJD96,
author = {Szabo, S. and Adam, P. and Janszky, J. and Domokos,
P.},
title = {Construction of quantum states of the radiation field
by discrete coherent-state superpositions},
journal = {Phys. Rev. A},
year = {1996},
volume = {53},
pages = {2698-2710},
abstract = {An efficient method of quantum state engineering based
on discrete superpositions of coherent states is presented. A
systematic method is developed for obtaining optimized
superpositions from the one-dimensional representation of the
desired state. It is shown that superposition of even a small
number of coherent states put along a straight line or on a circle
in phase space can approximate nonclassical field states with a
high degree of accuracy. An experimental scheme is proposed for
generating equidistant coherent-state superpositions on a circle
with arbitrary coefficients.}
}
@ARTICLE{BardroffMSDBRH96,
author = {Bardroff, P. J. and Mayr, E. and Schleich, W. P. and
Domokos, P. and Brune, M. and Raimond, J. M. and Haroche, S.},
title = {Simulation of quantum-state endoscopy},
journal = {Phys. Rev. A},
year = {1996},
volume = {53},
pages = {2736-2741},
abstract = {We demonstrate the experimental feasibility of
quantum-state endoscopy [P. J. Bardroff, E. Mayr, and W. P.
Schleich, Phys. Rev. A 51, 4963 (1995)] to measure the complete
quantum state of a single mode of the electromagnetic field in a
cavity. We perform numerical simulations of an experiment in
progress.}
}
@ARTICLE{PaulTKJ96,
author = {Paul, H. and Torma, P. and Kiss, T. and Jex, I.},
title = {Photon chopping: {New} way to measure the quantum state
of light},
journal = {Phys. Rev. Lett.},
year = {1996},
volume = {76},
pages = {2464-2467},
abstract = {We propose the use of a balanced 2N-port as a
technique to measure the pure quantum state of a single-mode light
field. In our scheme the coincidence signals of simple, realistic
photodetectors are recorded at the output of the 2N-port. We show
that applying different arrangements both the modulus and the phase
of the coefficients in a finite superposition state can be
measured. In particular, the photon statistics can be so measured
with currently available devices.
}
}
@ARTICLE{JanszkyKK96,
author = {Janszky, J. and Kim, M. G. and Kim, M. S.},
title = {Quasiprobabilities and the nonclassicality of fields},
journal = {Phys. Rev. A},
year = {1996},
volume = {53},
pages = {502-506},
abstract = {The existence of positive well-defined
quasiprobabilities is known to be related to the measure of
nonclassicality for a given field state. We test the coincidence of
the loss of wellknown nonclassical properties with the appearance
of the positive well-defined quasiprobabilities for various fields
influenced by phase-insensitive reservoirs. For Gaussian fields the
appearance of a positive Glauber-Sudarshan P function coincides
with the loss of nonclassical properties in quadrature fluctuations
and in photon statistics. We find that when an initial Fock state
dissipates or is amplified the initial field loses its
nonclassicality in photon statistics before the P function becomes
positive, which is different from the Gaussian field. The Wigner
function may be positive even when the decaying Fock state is
sub-Poissonian. For the amplification of the Pock state, however,
the Wigner function is positive only when the field is
super-Poissonian. For the dissipation and amplification of the Fock
state the point when a certain quasiprobability function becomes
positive definite depends only on the average number of photons N
of the heat bath.
}
}
@ARTICLE{VinogradovKJ95,
author = {Vinogradov, A. V. and Kobayashi, T. and Janszky, J.},
title = {A quantum molecular interferometer for measuring
femtosecond laser-pulses},
journal = {Opt. Spektrosk.},
year = {1995},
volume = {79},
pages = {343-347},
abstract = {}
}
@ARTICLE{DomokosRBH95,
author = {Domokos, P. and Raimond, J. M. and Brune, M. and
Haroche, S.},
title = {Simple cavity-qed 2-bit universal quantum logic gate -
the principle and expected performances},
journal = {Phys. Rev. A},
year = {1995},
volume = {52},
pages = {3554-3559},
abstract = {We present a simple scheme for a universal two-bit
quantum logic gate using circular Rydberg atoms and a
superconducting millimeter-wave cavity. We analyze in detail the
performances of this gate, using the parameters of an experiment
currently under way in our laboratory.
}
}
@ARTICLE{KissHL95,
author = {Kiss, T. and Herzog, U. and Leonhardt, U.},
title = {Compensation of losses in photodetection and in
quantum-state measurements},
journal = {Phys. Rev. A},
year = {1995},
volume = {52},
pages = {2433-2435},
abstract = {We show how losses in photodetection and in
quantum-state measurements can be numerically compensated after the
measurements have been performed. When the overall efficiency
exceeds 1/2, our recipe works for all quantum states. For smaller
efficiencies, however, the convergence of the compensation
procedure depends on the quantum state under investigation.
}
}
@ARTICLE{JanszkySBAP95,
author = {Janszky, J. and Sibilia, C. and Bertolotti, M. and
Adam, P. and Petak, A.},
title = {Properties of a directional coupler with parametric
amplification},
journal = {Quantum Semiclass. Opt.},
year = {1995},
volume = {7},
pages = {509-516},
abstract = {Properties of an optical field propagating inside a
directional coupler containing a parametric amplifying medium are
studied. Conditions for pump controlled, low noise switching
between the channels are analysed.
}
}
@ARTICLE{FoldesiAJ95,
author = {Foldesi, I. and Adam, P. and Janszky, J.},
title = {One-dimensional coherent-state representation of
squeezed displaced number states},
journal = {Phys. Lett. A},
year = {1995},
volume = {204},
pages = {16-20},
abstract = {The distribution function of the straight-line
coherent-state superpositions describing squeezed displaced number
states is derived. This one-dimensional representation is useful
for calculating physical quantities and essential for engineering
the states via discrete coherent-state superpositions.}
}
@ARTICLE{JanszkyDSA95,
author = {Janszky, J. and Domokos, P. and Szabo, S. and Adam,
P.},
title = {Quantum-state engineering via discrete coherent-state
superpositions},
journal = {Phys. Rev. A},
year = {1995},
volume = {51},
pages = {4191-4193},
abstract = {}
}
@ARTICLE{JanszkyPSBA95,
author = {Janszky, J. and Petak, A. and Sibilia, C. and
Bertolotti, M. and Adam, P.},
title = {Optical schrodinger-cat states in a directional
coupler},
journal = {Quantum Semiclass. Opt.},
year = {1995},
volume = {7},
pages = {145-152},
abstract = {The evolution of an optical Schrodinger-cat state in a
linear coupler is presented. It is shown how the quantum
interference of the cat state deteriorates and recovers along the
channels of the device. A similar behaviour of the photon number
distribution pattern is noted.
}
}
@ARTICLE{DomokosAJ94,
author = {Domokos, P. and Adam, P. and Janszky, J.},
title = {One-dimensional coherent-state representation on a
circle in phase-space},
journal = {Phys. Rev. A},
year = {1994},
volume = {50},
pages = {4293-4297},
abstract = {}
}
@ARTICLE{DomokosJA94,
author = {Domokos, P. and Janszky, J. and Adam, P.},
title = {Single-atom interference method for generating fock
states},
journal = {Phys. Rev. A},
year = {1994},
volume = {50},
pages = {3340-3344},
abstract = {An atomic interference method is presented that can be
used to construct arbitrary superpositions of coherent states with
equal mean photon number in a single-mode cavity by sending only
one atom through the apparatus. The method is suitable to generate
any quantum state that has a one-dimensional coherent state
representation on a circle in phase space. This method is
demonstrated in the case of generating Fock states.
}
}
@ARTICLE{JanszkyJ94,
author = {Janszky, J. and Janszky, J.},
title = {Squeezing and antisqueezing for a harmonic-oscillator
having a sudden change of mass - comment},
journal = {Phys. Rev. A},
year = {1994},
volume = {50},
pages = {3548-3550},
abstract = {It is shown that, contrary to the conclusions of a
paper by Baseia, De Brito, and Bagnato [Phys. Rev. A 45, 5308
(1992)], a harmonic oscillator can be squeezed by consecutive
sudden changes Of its mass to and back.
}
}
@ARTICLE{KissAJ94,
author = {Kiss, T. and Adam, P. and Janszky, J.},
title = {Time-evolution of a harmonic-oscillator - jumps
between 2 frequencies},
journal = {Phys. Lett. A},
year = {1994},
volume = {192},
pages = {311-315},
abstract = {The squeezing properties of a harmonic oscillator with
a series of sudden changes between two frequencies are determined.
Infinite, quasi-periodic and irregular behaviour of the squeezing
is found.
}
}
@ARTICLE{JanszkyVKK94,
author = {Janszky, J. and Vinogradov, A. V. and Kobayashi, T.
and Kis, Z.},
title = {Vibrational schrodinger-cat states},
journal = {Phys. Rev. A},
year = {1994},
volume = {50},
pages = {1777-1784},
abstract = {The optical Schrodinger-cat states are simple
realizations of quantum states having nonclassical features. It is
shown that vibrational analogs of such states can be realized in an
experiment of double-pulse or chirped-pulse excitation of vibronic
transitions. The possibility of conversion of vibrational
Schrodinger-cat states to chemical-cat states is discussed.
}
}
@ARTICLE{JanszkyVWM94,
author = {Janszky, J. and Vinogradov, A. V. and Walmsley, I. A.
and Mostowski, J.},
title = {Competition between geometrical and dynamical
squeezing during a franck-condon transition},
journal = {Phys. Rev. A},
year = {1994},
volume = {50},
pages = {732-740},
abstract = {The form of the molecular vibrational wave packet that
is generated when a short laser pulse excites a Franck-Condon
transition is examined. Particular attention is paid to the case
when the vibrational potentials in the ground and excited
electronic states have different characteristic frequencies and the
exciting pulse duration is sufficiently long that the nuclei move
during the excitation. It is shown that both the nonadiabatic
change in vibrational frequency and the vibrational dynamics can
cause squeezing of the resulting wave packet. For a pulse of
sufficiently short duration, and for molecules in which the nuclei
are more tightly bound in the excited electronic state, the
dynamical squeezing dominates that arising from the change of
vibrational frequency.}
}
@ARTICLE{KissJA94,
author = {Kiss, T. and Janszky, J. and Adam, P.},
title = {Time evolution of harmonic-oscillators with
time-dependent parameters - a step-function approximation},
journal = {Phys. Rev. A},
year = {1994},
volume = {49},
pages = {4935-4942},
abstract = {The time evolution of a quantum harmonic oscillator
with a series of sudden jumps of the mass or the frequency is
determined in the form of a recursion relation. An approximating
method is developed for determining the time evolution of harmonic
oscillators with arbitrary derivable functions of the frequency or
the mass. The approximate solution is shown to tend to the
analytical one in the limiting case. As a demonstration of the
approximating method, the solution of the problem of damped
oscillation in the square of the oscillator frequency is presented.
}
}
@ARTICLE{DomokosJAL94,
author = {Domokos, P. and Janszky, J. and Adam, P. and Larsen,
T.},
title = {Role of quantum interference in producing nonclassical
states},
journal = {Quantum Opt},
year = {1994},
volume = {6},
pages = {187-199},
abstract = {}
}
@ARTICLE{DomokosJ94,
author = {Domokos, P. and Janszky, J.},
title = {Interaction of schrodinger cats in optical processes},
journal = {Phys. Lett. A},
year = {1994},
volume = {186},
pages = {289-299},
abstract = {The propagation of optical Schrodinger cat states is
considered in beam-splitters and parametric amplifiers. Special
attention is paid to the evolution of the fringe pattern in the
Wigner function picture characteristic of the quantum interference
in Schrodinger cat states. The connection between the variation of
quantum features, especially the squeezing, and the evolution of
the fringe pattern in these optical processes is revealed. The
behaviour of the even coherent state in the amplification process
is compared with that of the squeezed coherent states.}
}
@ARTICLE{KisAJ94,
author = {Kis, Z. and Adam, P. and Janszky, J.},
title = {Properties of states generated by excitations on the
amplitude squeezed state},
journal = {Phys. Lett. A},
year = {1994},
volume = {188},
pages = {16-20},
abstract = {The properties of the states generated by excitations
on the amplitude squeezed state are examined. It is shown that the
field in such states exhibits quadrature squeezing and the amount
of sub-Poissonian statistics is enhanced as the degree of the
excitation increases. Quasiprobability functions are presented.
}
}
@ARTICLE{AdamFJ94,
author = {Adam, P. and Foldesi, I. and Janszky, J.},
title = {Complete basis-set via straight-line coherent-state
superpositions},
journal = {Phys. Rev. A},
year = {1994},
volume = {49},
pages = {1281-1287},
abstract = {The properties of one-dimensional straight-line
superposition states obtained as a continuous generalization of the
even and odd coherent states are studied. Superposition states with
Hermite-polynomial-Gaussian distribution functions are introduced.
These states form a complete orthonormal basis set in the Hilbert
space of quantum oscillators. This basis makes it possible to
obtain the straight, line coherent-state distribution function for
a given state. As an example, the distribution functions for
squeezed coherent states are derived.
}
}
@ARTICLE{JanszkyAVK93,
author = {Janszky, J. and Adam, P. and Vinogradov, A. V. and
Kobayashi, T.},
title = {Vibrational-state shaping for selective laser
chemistry},
journal = {Chem. Phys. Lett.},
year = {1993},
volume = {213},
pages = {368-372},
abstract = {Wave packets of phonon states with special properties
can be formed during electronic excitation of molecules by short
chirped laser pulses. In particular it is shown that extreme
localization (squeezing) of the vibrational state can be achieved.
The application of this effect in selective laser chemistry is
discussed.
}
}
@ARTICLE{JanszkyDA93,
author = {Janszky, J. and Domokos, P. and Adam, P.},
title = {Coherent states on a circle and quantum interference},
journal = {Phys. Rev. A},
year = {1993},
volume = {48},
pages = {2213-2219},
abstract = {As a generalization of the optical Schrodinger cats,
discrete sets of coherent states are considered on a circle in the
a plane. It is shown that simple superpositions of Schrodinger cats
exhibit amplitude squeezing, similarly to the case of a
superposition of several coherent states along a straight line that
shows quadrature squeezing. The interference fringes between the
coherent states form the annuli of the Fock states inthe
Wigner-function picture. It is also shown that a continuous
superposition of coherent states on a circle can serve as a basis
for the representation of any state.}
}
@ARTICLE{JanszkyAF93,
author = {Janszky, J. and Adam, P. and Foldesi, I.},
title = {Sudden mass changes of a quantum oscillator and
squeezing},
journal = {Phys. Lett. A},
year = {1993},
volume = {174},
pages = {368-370},
abstract = {It is shown that a high degree of squeezing can be
achieved by a series of sudden mass changes of a quantum
oscillator. A strong dependence of the squeezing on the time
interval between the mass jumps from M1 to M2 and back is found.
}
}
@ARTICLE{FoldesiAJ93,
author = {Foldesi, I. and Adam, P. and Janszky, J.},
title = {Antisymmetric straight-line superposition of coherent
states},
journal = {Phys. Lett. A},
year = {1993},
volume = {173},
pages = {97-100},
abstract = {It is shown that a continuous generalization of the
odd Schrodinger-cat state emerging from the annihilation of one
photon in the squeezed vacuum state shows remarkable nonclassical
properties such as squeezing at mean photon number higher than 2
and sub-Poissonian photon statistics.
}
}
@ARTICLE{JanszkyA92,
author = {Janszky, J. and Adam, P.},
title = {Strong squeezing by repeated frequency jumps},
journal = {Phys. Rev. A},
year = {1992},
volume = {46},
pages = {6091-6092},
abstract = {The consequences of sudden frequency changes of a
quantum oscillator from omega1 to omega2 and back is considered. A
strong dependence of squeezing on the time interval between the
frequency jumps is found. It is shown that a high degree of
squeezing can be achieved by a series of sudden frequency changes.
}
}
@ARTICLE{JanszkyAY92,
author = {Janszky, J. and Adam, P. and Yushin, Y.},
title = {Direct detection of squeezing in photocount
coincidence experiments},
journal = {Opt. Commun.},
year = {1992},
volume = {93},
pages = {191-194},
abstract = {It is shown that the parameters characterising the
squeezed light can be determined by measuring the coincidence of
photocounts.
}
}
@ARTICLE{JanszkyABS92,
author = {Janszky, J. and Adam, P. and Bertolotti, M. and
Sibilia, C.},
title = {Amplitude-squeezed number-phase intelligent states in
a directional coupler},
journal = {Quantum Opt},
year = {1992},
volume = {4},
pages = {163-172},
abstract = {The evolution of number-phase intelligent states in a
directional coupler is studied looking at the conditions to reach
the minimum number of photons needed for switching.}
}
@ARTICLE{JanszkyAV92,
author = {Janszky, J. and Adam, P. and Vinogradov, A. V.},
title = {Superposition of coherent states and squeezing -
reply},
journal = {Phys. Rev. Lett.},
year = {1992},
volume = {68},
pages = {3816-3816},
abstract = {}
}
@ARTICLE{JanszkyBSKA91,
author = {Janszky, J. and Bertolotti, M. and Sibilia, C. and
Kobayashi, T. and Adam, P.},
title = {Optical-processing of nonclassical light},
journal = {Inst. Phys. Conf. Ser.},
year = {1991},
volume = {},
pages = {31-38},
abstract = {The optical processing of such nonclassical states as
the squeezed and the photon number states of light are discussed in
a unitary way.
}
}
@ARTICLE{JanszkyAVK92,
author = {Janszky, J. and Adam, P. and Vinogradov, A. V. and
Kobayashi, T.},
title = {Influence of phonon squeezing on the transient
spectrum},
journal = {Spectroc. Acta Pt. A-Molec. Biomolec. Spectr.},
year = {1992},
volume = {48},
pages = {31-39},
abstract = {Changes of the transient electronic spectrum of
molecules, due to the formation of squeezed-like phonon states, are
calculated in pump and probe experiments. After an ultrashort
excitation, this effect typically changes both the spectrum's
position and shape, periodically. The amplitude of the effect
decreases while the system relaxes towards steady state through
dephasing.
}
}
@ARTICLE{AdamJV91,
author = {Adam, P. and Janszky, J. and Vinogradov, A. V.},
title = {Amplitude squeezed and number-phase intelligent states
via coherent state superposition},
journal = {Phys. Lett. A},
year = {1991},
volume = {160},
pages = {506-510},
abstract = {It is shown that Gaussian superpositions of coherent
states along an are are approximate number-phase intelligent states
associated with the Pegg-Barnett phase operator and describe
amplitude squeezing.
}
}
@ARTICLE{JanszkySB91,
author = {Janszky, J. and Sibilia, C. and Bertolotti, M.},
title = {Photon number-distribution in a linear directional
coupler},
journal = {J. Mod. Opt.},
year = {1991},
volume = {38},
pages = {2467-2477},
abstract = {The photon counting distribution of two modes in a
directional coupler is studied, looking in particular at the
behaviour of photon number states when losses are taken into
account.}
}
@ARTICLE{AdamJV90,
author = {Adam, P. and Janszky, J. and Vinogradov, A. V.},
title = {Gaussian coherent state expansion of the squeezed
states},
journal = {Opt. Commun.},
year = {1990},
volume = {80},
pages = {155-158},
abstract = {It is shown that gaussian coherent state expansions
describe squeezed states. The non-analytic gaussian expansion
allows to reduce the dimensionality of the representation. Using
this very convenient representation we calculated the quantities
[a(dagger-j)a(k)], which immediately give the mean value of any
normally ordered operator function F(a(dagger), a).
}
}
@ARTICLE{AdamJ90,
author = {Adam, P. and Janszky, J.},
title = {Coherent state expansion of squeezed states},
journal = {Phys. Lett. A},
year = {1990},
volume = {149},
pages = {67-70},
abstract = {}
}
@ARTICLE{VinogradovJ90,
author = {Vinogradov, A. V. and Janszky, J.},
title = {New mechanism of molecule vibrations squeezing during
franckcondon transition},
journal = {Acta Phys. Pol. A},
year = {1990},
volume = {78},
pages = {231-237},
abstract = {}
}
@ARTICLE{JanszkyV90,
author = {Janszky, J. and Vinogradov, A. V.},
title = {Squeezing via one-dimensional distribution of coherent
states},
journal = {Phys. Rev. Lett.},
year = {1990},
volume = {64},
pages = {2771-2774},
abstract = {}
}
@ARTICLE{JanszkyKV90,
author = {Janszky, J. and Kobayashi, T. and Vinogradov, A. V.},
title = {Phonon squeezing in chirped pulse pump and probe
experiments},
journal = {Opt. Commun.},
year = {1990},
volume = {76},
pages = {30-33},
abstract = {}
}
@ARTICLE{JanszkyK90,
author = {Janszky, J. and Kobayashi, T.},
title = {Effects of damping and reamplification of pure number
states},
journal = {Phys. Rev. A},
year = {1990},
volume = {41},
pages = {4074-4076},
abstract = {}
}
@ARTICLE{JanszkyY89,
author = {Janszky, J. and Yushin, Y.},
title = {Asymmetric light and multiphoton processes},
journal = {J. Mod. Opt.},
year = {1989},
volume = {36},
pages = {1003-1009},
abstract = {}
}
@ARTICLE{JanszkyY89b,
author = {Janszky, J. and Yushin, Y.},
title = {Amplification of squeezed light and multiphoton
processes},
journal = {Phys. Lett. A},
year = {1989},
volume = {137},
pages = {451-452},
abstract = {}
}
@ARTICLE{JanszkyY89c,
author = {Janszky, J. and Yushin, Y.},
title = {Squeezing and frequency jump of a harmonic-oscillator
- comment},
journal = {Phys. Rev. A},
year = {1989},
volume = {39},
pages = {5445-5446},
abstract = {}
}
@ARTICLE{JanszkySBY88,
author = {Janszky, J. and Sibilia, C. and Bertolotti, M. and
Yushin, Y.},
title = {Non-classical light in a linear coupler},
journal = {J. Mod. Opt.},
year = {1988},
volume = {35},
pages = {1757-1765},
abstract = {}
}
@ARTICLE{JanszkySBY88b,
author = {Janszky, J. and Sibilia, C. and Bertolotti, M. and
Yushin, Y.},
title = {Switch effect of nonclassical light},
journal = {J Phys-Paris},
year = {1988},
volume = {49},
pages = {337-339},
abstract = {}
}
@ARTICLE{KarpatiK03,
author = {Karpati, A. and Kis, Z.},
title = {Adiabatic creation of coherent superposition states
via multiple intermediate states},
journal = {J. Phys. B-At. Mol. Opt. Phys.},
year = {2003},
volume = {36},
pages = {905-919},
abstract = {We consider an adiabatic population transfer process
that resembles the well-established stimulated Raman adiabatic
passage. In our system, the states have nonzero angular momentums
J, therefore, the coupling laser fields induce transitions between
the magnetic sublevels of the states. In particular, we discuss the
possibility of creating coherent superposition states in a system
with coupling pattern J = 0 double left right arrow1 and 1 double
left right arrow 2. Initially, the system is in the J = 0 state. We
show that by, applying two delayed overlapping laser pulses, it is
possible to create any final superposition state of the magnetic
sublevels \2, -2], \2, 0], \2, +2]. Moreover, we find that the
relative phases of the applied pulses influence not only the phases
of the final superposition state but also the probability
amplitudes. We show that if we fix the shape and the time delay
between the pulses, the final state space can be entirely covered
by varying the polarizations and relative phases of the two pulses.
Performing numerical simulations we find that our transfer process
is nearly adiabatic for the whole parameter set.
}
}
@ARTICLE{PaspalakisK02,
author = {Paspalakis, E. and Kis, Z.},
title = {Enhanced nonlinear generation in a three-level medium
with spatially dependent coherence},
journal = {Opt. Lett.},
year = {2002},
volume = {27},
pages = {1836-1838},
abstract = {We consider a method for efficient parametric
generation of a laser pulse. A single laser field is injected into
a threelevel medium that has two lower states and one excited
state. The lower states are initially prepared in a
position-dependent coherent superposition state. It is shown that,
by proper choice of the position dependence of the superposition
along the direction of propagation, the incoming field can be
completely converted to a new field. (C) 2002 Optical Society of
America.
}
}
@ARTICLE{PaspalakisK02b,
author = {Paspalakis, E. and Kis, Z.},
title = {Pulse propagation in a coherently prepared multilevel
medium},
journal = {Phys. Rev. A},
year = {2002},
volume = {66},
pages = {art. no.-025802},
abstract = {We present an analytical solution of the coupled
Maxwell-Bloch equations for the case of a laser-driven and
coherently prepared medium with one upper state and N lower states.
We show that under specific conditions the medium can become either
completely opaque or completely transparent to the laser pulses. We
also study the potential for efficient parametric generation of N-m
laser pulses and show that this is possible by injecting the system
with m input pulses.
}
}
@ARTICLE{KisR02,
author = {Kis, Z. and Renzoni, F.},
title = {Qubit rotation by stimulated Raman adiabatic passage},
journal = {Phys. Rev. A},
year = {2002},
volume = {65},
pages = {art. no.-032318},
abstract = {We introduce a procedure for qubit rotation,
alternative to the commonly used method of Rabi oscillations of
controlled pulse area. It is based on the technique of stimulated
Raman adiabatic passage and, therefore, it is robust against
fluctuations of experimental parameters. Furthermore, our work
shows that it is, in principle, possible to perform quantum logic
operations via stimulated Raman adiabatic passage. This opens up
the search for a completely new class of schemes to implement logic
gates.
}
}
@ARTICLE{KisS02,
author = {Kis, Z. and Stenholm, S.},
title = {Optimal control approach for a degenerate STIRAP},
journal = {J. Mod. Opt.},
year = {2002},
volume = {49},
pages = {111-124},
abstract = {We have looked at the laser-induced excitation of a
level manifold coupled through a single excited level. This
generalizes the ordinary A configuration to many levels. It is the
original situation where stimulated Raman adiabatic passage
(STIRAP) has been considered. We then apply optimal control theory
to determine the pulse sequence which effects a predetermined
superposition state with a minimal involvement of the excited
state. The program is free to find its optimal pulse sequence, and
we find that a generalization of the ordinary counterintuitive
situation emerges. In addition to verifying the efficiency of the
counterintuitive approach, the work justifies the separation into
dark and bright subspaces, where time evolution in the former has
to include the dynamical effects of adiabatic corrections.
}
}
@ARTICLE{KisS01,
author = {Kis, Z. and Stenholm, S.},
title = {Nonadiabatic dynamics in the dark subspace of a
multilevel stimulated Raman adiabatic passage process},
journal = {Phys. Rev. A},
year = {2001},
volume = {6406},
pages = {art. no.-063406},
abstract = {In this paper we consider a generalization of the
three-level stimulated Raman adiabatic-pas sage process (STIRAP).
In our scheme, there are N-1 ground levels and one excited level.
The ground levels are coupled with laser pulses through the excited
level at multiphoton resonance. The ultimate aim of this scheme is
to create coherent-superposition states on the ground levels. In a
previous paper [J. Mod. Opt. (to be published), special issue on
quantum interference] we have considered this problem from the
optimal-control point of view. Here we apply a different approach:
We reconsider the adiabatic approximation, which is commonly
utilized to describing the STIRAP process. It is shown that in our
case, in the adiabatic limit, the dark and bright subspaces of the
Hamiltonian are decoupled; however, the nonadiabatic corrections
influence significantly the dynamics in the dark subspace. An
analytic solution is presented for the case of a five-level system.
Moreover, we consider some special examples for the pulse sequences
that effect prescribed final superposition states. The robustness
of the scheme is studied, and the extension of our scheme is also
considered.
}
}
@ARTICLE{KisS01a,
author = {Kis, Z. and Stenholm, S.},
title = {Measuring the density matrix by local addressing},
journal = {Phys. Rev. A},
year = {2001},
volume = {6406},
pages = {art. no.-065401},
abstract = {We introduce a procedure to measure the density matrix
of a material system. The density matrix is addressed locally in
this scheme by applying a sequence of delayed-light pulses. The
procedure is based on the stimulated Raman adiabatic passage
technique. It is shown that a series of population measurements on
the target state of the population transfer process yields
unambiguous information about the populations and coherences of the
addressed states, which, therefore, can be determined.}
}
@ARTICLE{KisVD01,
author = {Kis, Z. and Vogel, W. and Davidovich, L.},
title = {Nonlinear coherent states of trapped-atom motion},
journal = {Phys. Rev. A},
year = {2001},
volume = {6403},
pages = {art. no.-033401},
abstract = {The general character of nonlinear coherent states
(NCS) is considered. A method is introduced by which any pure state
of the quantum harmonic oscillator can be represented in a limiting
sense as a NCS. The representation of a Fock state as a NCS is
discussed in detail. As a physical example we show how to prepare a
highly excited Fock state in an ion trap based on the concept of
NCS.
}
}
@ARTICLE{KisVDZ01,
author = {Kis, Z. and Vogel, W. and Davidovich, L. and Zagury,
N.},
title = {Dark SU(2) states of the motion of a trapped ion},
journal = {Phys. Rev. A},
year = {2001},
volume = {6305},
pages = {art. no.-053410},
abstract = {The preparation of SU(2) states as dark states of the
motion of a trapped ion is considered. The difficulty in preparing
these states is shown to arise from the degeneracy of eigenvalues
of the Hamiltonian. This degeneracy is removed by making use of the
nonlinearities appearing in the dynamics of an ion that is not well
localized. The mechanism of approaching the dark state of interest
is analyzed by using the quantum trajectory method.}
}
@ARTICLE{DomokosKJZKV00,
author = {Domokos, P. and Kiss, T. and Janszky, J. and
Zucchetti, A. and Kis, Z. and Vogel, W.},
title = {Collapse and revival in the vibronic dynamics of
laser-driven diatomic molecules},
journal = {Chem. Phys. Lett.},
year = {2000},
volume = {322},
pages = {255-262},
abstract = {Resonant driving of certain electronic transitions in
diatomic molecules is shown to yield collapses and revivals of the
electronic populations due to the quantized vibrational motion of
the nuclei. We analyze the properties of the vibrational
potentials, the frequency and power of the classical driving laser
field for which this effect can be observed. (C) 2000 Elsevier
Science B.V. All rights reserved.
}
}
@ARTICLE{DiFidioWKV99,
author = {Di Fidio, C. and Wallentowitz, S. and Kis, Z. and
Vogel, W.},
title = {Quantum-jump effects in the motion of a Raman-driven
trapped ion},
journal = {Phys. Rev. A},
year = {1999},
volume = {60},
pages = {R3393-R3396},
abstract = {Rarely occurring single-photon electronic transitions
in the Raman-driven quantized motion of a trapped ion are
considered. Using a quantum trajectory approach it is demonstrated
that these transitions, which are usually ignored, may cause
significant quantum decoherence effects. In addition, we find an
asymmetric evolution in the Wigner function due to induced
transitions of a nonsymmetric type. [S1050-2947(99)51511-4].}
}
@ARTICLE{KisKJAWV99,
author = {Kis, Z. and Kiss, T. and Janszky, J. and Adam, P. and
Wallentowitz, S. and Vogel, W.},
title = {Local sampling of phase-space distributions by
cascaded optical homodyning},
journal = {Phys. Rev. A},
year = {1999},
volume = {59},
pages = {R39-R42},
abstract = {We propose the determination of phase-space
distributions of optical fields by cascaded optical homodyning,
where phaserandomized balanced homodyning is used for measuring
the output photon-number statistics of an unbalanced homodyne
detection scheme. The phase-space point of interest is controlled
by the complex amplitude of the local oscillator and a universal
sampling function is sufficient for mapping the measured quadrature
statistics onto the phase-space distribution.
[S1050-2947(99)50201-1].
}
}
@ARTICLE{KisJAVK96,
author = {Kis, Z. and Janszky, J. and Adam, P. and Vinogradov,
A. V. and Kobayashi, T.},
title = {Entangled vibrational states in polyatomic molecules},
journal = {Phys. Rev. A},
year = {1996},
volume = {54},
pages = {5110-5117},
abstract = {The vibrational state of a polyatomic molecule excited
with a transform limited light pulse is determined analytically. We
analyze how the properties of the vibrational state depend on the
duration of the exciting pulse and the possible geometrical
configurations of the nuclear potential surfaces. It is pointed out
that a finite exciting pulse results in an entangled vibrational
state. The magnitude of the entanglement is described by the von
Neumann entropy associated with the vibrational modes. It is shown
that in the case of a very short excitation, the change of the
geometrical configuration of the vibrionic potential surface may
also lead to entanglement.}
}
@ARTICLE{SzaboKAJ94,
author = {Szabo, S. and Kis, Z. and Adam, P. and Janszky, J.},
title = {Number-phase uncertainty properties of the gaussian
arc distribution state},
journal = {Quantum Opt},
year = {1994},
volume = {6},
pages = {527-539},
abstract = {A method is developed for constructing a [-pi, pi] are
distribution function of one-dimensional coherent state
superpositions on a circle from the [-infinity, infinity] weight
function. Changing the parameters of a Gaussian weight function
superposition states with different amplitude-squeezed and
number-phase uncertainty properties can be prepared.}
}
@Article{JanszkyY87,
author = {J. Janszky and Y. Yushin},
title = {Many-photon processes with the participation of squeezed light},
journal = {Phys. Rev. A},
year = {1987},
volume = {36},
number = {3},
pages = {1288-1292},
month = {August},
abstract = {The description of an electromagnetic field of complicated statistics
with noise, coherent, and squeezed features are discussed using the
nondiagonal coherent-state representation of the density matrix and
the normally ordered characteristic function derived therefrom. The
quantity <(a+)nan> which plays a central role in the theory of
many-photon processes is found for this field. Particular cases with
dominant coherent signal, noise, or squeezing are discussed. It is
found that the ratios <(a+)nan>/()n for the coherent, the
chaotic, and the strongly squeezed vacuum states are 1, n!, and
(2n-1)!!, respectively. The value of <(a+)n> related to the anomalous
coherence function is considered. It is found that the noise does not
influence <(a+)n>.}
}
@Article{JanszkyY86,
author = {J. Janszky and Y. Y. Yushin},
title = {Squeezing vie frequency jump},
journal = {Opt. Commun.},
year = {1986},
volume = {59},
number = {2},
pages = {151-154},
month = {August},
abstract = {It is shown that a sudden frequency change of a quantum
oscillator e.g. during a Franck-Condon transition leads to squeezing.
The characteristic function and the density operator of this squeezed
state are considered.}
}
@Article{LeonhardtKO03,
author = {U. Leonhardt and T. Kiss and P. Ohberg},
title = {Bogoliubov theory of the {Hawking} effect in
{Bose-Einstein} condensates},
journal = {J. Opt. B-Quantum Semicl. Opt.},
volume = {5},
year = {2003},
pages = {S42-S49},
number= {2},
month = {April},
abstract = {Artificial black holes may demonstrate some of the elusive
quantum properties of the event horizon, in particular Hawking
radiation. One promising candidate is a sonic hole in a Bose-
Einstein condensate. We clarify why Hawking radiation emerges from
the condensate and how this condensed-matter analogue reflects
some of the intriguing aspects of quantum black holes.}
}
@Article{LeonhardtTO03,
author = {U. Leonhardt and T. Kiss and P. Ohberg},
title = {Theory of elementary excitations in unstable
{Bose-Einstein} condensates and the instability of sonic horizons},
journal = {Phys. Rev. A},
volume = {67},
number = {3},
year = {2003},
pages = {art. no.-033602},
month = {March},
abstract = {Like classical fluids, quantum gases may suffer from
hydrodynamic instabilities. Our paper develops a quantum version
of the classical stability analysis in fluids, the Bogoliubov
theory of elementary excitations in unstable Bose- Einstein
condensates. In unstable condensates the excitation modes have
complex frequencies. We derive the normalization conditions for
unstable modes such that they can serve in a mode decomposition of
the noncondensed component. Furthermore, we develop approximative
techniques to determine the spectrum and the mode functions.
Finally, we apply our theory to sonic horizons-sonic black and
white holes. For sonic white holes the spectrum of unstable modes
turns out to be intrinsically discrete, whereas black holes may be
stable.}
}
@Article{LeonhardtKP00,
author = {U. Leonhardt and T. Kiss and P. Piwnicki},
title = {Quantum backaction of optical observations on
{Bose-Einstein} condensates},
journal = {Eur. Phys. J. D},
volume = {12},
number = {1},
pages= {124-124},
month= {October},
year = {2000},
abstract = {}
}
@Article{LeonhardKP99,
author = {U. Leonhardt and T. Kiss and P. Piwnicki},
title = {Quantum backaction of optical observations on
{Bose-Einstein} condensates},
journal = {Eur. Phys. J. D},
volume = {7},
number = {3},
pages = {413-423},
year = {1999},
month= {October-November},
abstract = {Impressive pictures of moving Bose-Einstein condensates
have been taken using phase-contrast imaging [M.R. Andrews et al.,
Science 273: 84 (1996)]. We calculate the quantum backaction of
this measurement technique, assuming the absence of residual
absorption. We find that the condensate gets gradually depleted at
a universal rate that is proportional to the light intensity and
to the inverse cube of the optical wave length. The fewer atoms
are condensed the higher is the required intensity to see a
picture, and, consequently, the higher is the induced backaction.
To describe the quantum physics of phase-contrast imaging we put
forward a new approach to quantum-optical propagation. We develop
an effective field theory of paraxial optics in a fully quantized
atomic medium.}
}
@Article{LeonhardtKB99,
author = {U. Leonhardt and T. Kiss and P. J. Bardroff},
title = {State reconstruction of wave packets moving in
time-dependent potentials and the existence of {Wronskian} pairs},
journal = {J. Phys. A-Math. Gen.},
volume = {32},
number = {2},
pages = {411-418},
year = {1999},
month= {January},
abstract = {We determine a class of time-dependent potentials that
support the state reconstruction of one-dimensional wave packets.
For this we extend the projection method (Leonhardt U and Raymer M
G 1996 Phys. Rev. Lett. 76 1985) to explicitly time-dependent
situations. We require the existence of Wronskian pairs (regular
and irregular wavefunctions) and analyse the consequences on the
possible potentials.}
}
@Article{PaulTKJ97b,
author = {H. Paul and P. Torma and T. Kiss and I. Jex},
title = {Two-mode state reconstruction using photon chopping},
journal = {J. Mod. Opt.},
volume = {44},
number= {11-12},
pages= {2395-2404},
year = {1997},
month= {November-December},
abstract = {The reconstruction of the complete quantum state of a pure-
state two-mode field is shown to be possible by the photon-
chopping method, that is, by spreading the signal with balanced
multiports over an array of detectors and by measuring
coincidences. In particular, correlations between the two modes
can be detected with high efficiency.}
}
@ARTICLE{FarkasKW02,
author = {Farkas, S. and Kurucz, Z. and Weiner, M.},
title = {Poincare covariance of relativistic quantum position},
journal = {Int. J. Theor. Phys.},
year = {2002},
volume = {41},
number = {1},
pages = {79-88},
abstract = {A great number of problems of relativistic position in
quantum mechanics are because of the use of coordinates that are
not inherent objects of spacetime, cause unnecessary complications,
and can lead to misconceptions. We apply a coordinate-free approach
to rule out such problems. Thus it will be clear, for example, that
the Lorentz covariance of position, required usually on the analogy
of Lorentz covariance of spacetime coordinates, is not well posed
and we show that in a right setting the Newton-Wigner position is
Poincare covariant.}
}
@Article{KuruczKAJ03,
author = {Z. Kurucz and M. Koniorczyk and P. Adam and
J. Janszky},
title = {An operator description of entanglement matching in
quantum teleportation},
journal = {J. Opt. B: Quantum Semiclass. Opt.},
year = 2003,
volume = 5,
number = 6,
pages = {S627-S632},
month = nov,
url = {http://stacks.iop.org/1464-4266/5/S627},
abstract = {The antilinear operator representation of bipartite
pure states of the relative state formulation of
quantum mechanics is applied to describe quantum
teleportation schemes utilizing an arbitrary pure
state as the entangled resource. Bennett type
teleportation schemes with nonmaximally entangled
pure states are characterized and the notion of
'entanglement matching' is introduced in
general. Examples, including a scheme based on
coherent-state superposition states of the
electromagnetic field, are provided.}
}