T. Opatrny - Abstracts of
Publications
(2007)
- M. Kolář, T.
Opatrný, N. Bar-Gill, N. Erez, and G. Kurizki,
Path-phase duality with intraparticle translational-internal
entanglement.
New J. Phys. 9, 129 (2007)
. (e-print
arXiv:0705.4177v1 [quant-ph])
(e-print arXiv:0705.4177v1 [quant-ph])
Abstract:
The aim of this paper is to revisit the implications of
complementarity when we inject into a Mach Zehnder interferometer
particles with internal structure, prepared in special
translational-internal entangled (TIE) intraparticle states. This
correlation causes the path distinguishability to be interferometric
phase-dependent in contrast to the standard case, where
distinguishability depends on some external parameters ( not
interferometric phase). We show that such a TIE state permits us to
detect small phase shifts along with almost perfect path
distinguishability, beyond the constraints imposed by complementarity
on simultaneous which-way and which-phase measurements for cases when
distinguishability is uncoupled to interferometric phase.
(2006)
- M. Kolář, T. Opatrný, N.
Bar-Gill, and G. Kurizki,
Betting on interferometric paths and phases using translational-internal
entanglement: The greedy king game.
Int. J. Mod. Phys. B 20, 11-13 (2006).
Abstract:
The behavior of translationally internally entangled (TIE) states
in an interferometer of the Mach-Zehnder type is studied, by means of a
game whose results show that TIE states allow near-certain guessing of
both path (corpuscular) and phase (wavelike) features, as opposed to
conventional states that axe constrained by standard complementarity.
- G. Kurizki, N. Bar-Gill, J.
Clausen, M. Kolář, and
T. Opatrný,
Cheating on complementarity and interference by
translational-internal entanglement.
Quantum Information Processing 5, 463-479
(2006).
Abstract:
We show that if internal and momentum states of an interfering
particle are entangled, then by measuring its internal state we may
infer both path (corpuscular) and phase (wavelike) information with
practically any precision, without the complementarity constraints of
which-path detection. This holds also for multipath-multistate
configurations, allowing large amounts of information to be stored in a
single particle. We further show that highly complex particles (e.g.,
molecules or macroscopic bodies) subject to fields that couple
(entangle) their internal and translational (momentum) states may
undergo an irresversible randomization (diffusion), manifest by the
disappearance of the interference pattern, as if they are subject to
decoherence. Thus, translational-internal entanglement can give rise to
anomalies in quantum wavepacket propagation.
- J. Fiurášek, J.
Sherson, T. Opatrný,
and E.S. Polzik,
Single-passage readout of atomic quantum memory.
Phys. Rev. A 73, 022331 (2006). (e-print quant-ph/0510099)
Abstract:
A scheme for retrieving quantum information stored in collective
atomic spin systems onto optical pulses is presented. Two off-resonant
light pulses cross the atomic medium in two orthogonal directions and
are interferometrically recombined in such a way that one of the
outputs carries most of the information stored in the medium. In
contrast to previous schemes our approach requires neither multiple
passes through the medium nor feedback on the light after passing the
sample, which makes the scheme very efficient. The price for that is
some added noise which is, however, small enough for the method to beat
the classical limits.
- T. Opatrný,
Single-cell atomic quantum memory for light.
Phys. Rev A 74, 043809 (2006).
(e-print quant-ph/0509094)
Abstract:
Recent experiments demonstrating atomic quantum memory for light
[B. Julsgaard , Nature 432, 482 (2004)] involve two macroscopic samples
of atoms, each with opposite spin polarization. It is shown here that a
single atomic cell is enough for the memory function if the atoms are
optically pumped with suitable linearly polarized light, and quadratic
Zeeman shift and/or ac Stark shift are used to manipulate rotations of
the quadratures. This should enhance the performance of our quantum
memory devices since less resources are needed and losses of light in
crossing different media boundaries are avoided.
(2005)
- T.
Opatrný and J. Fiurášek,
Enhancing the capacity and
performance of collective atomic quantum memory.
Phys. Rev. Letters 95, 053602 (2005). (e-print quant-ph/0502135)
Abstract:
Present schemes involving the quantum nondemolition
interaction
between atomic samples and off-resonant light pulses allow
us to store quantum information corresponding to a single harmonic
oscillator (mode) in one multiatomic system. We discuss the possibility
of involving several coherences of each atom so that the atomic sample
can store information contained in several quantum modes. This is
achieved by the coupling of different magnetic sublevels of the
relevant hyperfine level by additional Raman pulses. This technique
allows us to design not only the quantum nondemolition
coupling, but
also beam splitterlike and two-mode squeezerlike interactions between
light and collective atomic spin.
- T.
Opatrný,
The maser as a reversible
heat engine.
Am. J. Phys. 73, 63-68 (2005).
Abstract:
In a maser, a state selector sends excited molecules or atoms
to a resonant cavity, while ground-level particles are not allowed to
enter the resonator. The excited particles radiate their energy in the
form of coherent electromagnetic oscillation. In this way the thermal
energy of the atoms is transformed into useful work. Is this
transformation equivalent to the Maxwell demon violating the second
law? We explain the thermodynamics of an idealized maser system which
works as a reversible heat engine and show how the second law reveals
its validity during the conversion of heat into coherent radiation and
mechanical work. We discuss different working regimes of the system. In
particular, the ideal engine can either work with two heat reservoirs
and convert heat into maser radiation with the Carnot efficiency, or,
if
working with a single heat reservoir, the engine can convert mechanical
work entirely into maser radiation.
- T.
Opatrný, M. Kolář, and G. Kurizki,
Position and momentum
entanglement of dipole-dipole interacting atoms in optical lattices.
In: M.V. Akulin at al. (ed.), Decoherence, Entanglement and Information
Protection in Complex Quantum Systems, 373-390 (Springer 2005).
Abstract:
We consider a possible
realization of the position- and momentum-correlated atomic pairs that
are confined to adjacent sites of two mutually shifted optical lattices
and are entangled via laser-induced dipole-dipole interactions. The
Einstein-Podolsky-Rosen (EPR) "paradox" [Einstein 1935] with
translational variables is then modified by lattice-diffraction
effects. We study a possible mechanism of creating such diatom
entangled states by varying the effective mass of the atoms.
- T.
Opatrný, M. Arndt, T.F. Gallagher, R. Garcia-Fernandez, S.
Haroche, M. Leibscher, P. Pillet, and J. Sherson,
Internal-translational entanglement entanglement in atoms and
molecules.
In: M.V. Akulin at al. (ed.), Decoherence, Entanglement and Information
Protection in Complex Quantum Systems, 317-324 (Springer 2005).
- G.
Beadie, Z.E. Sariyanni, Y. V.
Rostovtsev, T. Opatrny, J. Reintjes, and M.O. Scully,
Towards
a FAST CARS anthrax
detector: coherence preparation using simultaneous femtosecond laser
pulses.
Optics Comm. 244,
423-430 (2005).
Abstract: Maximizing
the molecular response to coherent anti-Stokes Raman spectroscopy
(CARS) requires optimizing the preparation of a vibrational quantum
coherence. We simulate the amount of laser-induced coherence prepared
in a three-level system modeled after dipicolinic acid (DPA), a marker
molecule for bacterial spores. The level spacings and decoherence times
were chosen to agree with experimental data observed from DPA.
Nearly-maximal vibrational coherences can be induced for 150 fs optical
pulses, despite the very fast dephasing rates of the electronic
transitions. It is also shown that pulse propagation effects play an
important role in the development of coherence throughout an extended
sample, due to nonlinear index effects of the molecule at the laser
frequencies.
(2004)
- T. Opatrný, M.
Kolář, G. Kurizki, and B. Deb,
Position and momentum
entanglement of dipole-dipole interacting atoms in optical lattices:
The Einstein-Podolsky-Rosen paradox on a lattice.
Int. J. Quantum Information 2, 305-321 (2004)
.
Abstract:
We study a possible realization of the position- and
momentum-correlated atomic pairs that are confined to adjacent sites of
two mutually shifted optical lattices and are entangled via
laser-induced dipole-dipole interactions. The Einstein-Podolsky-Rosen
(EPR) "paradox"(1) with translational variables is then modified by
lattice-diffraction effects. This "paxadox" can be verified to a high
degree of accuracy in this scheme.
(2003)
- T.
Opatrny, B. Deb, and G. Kurizki
Proposal for translational
entanglement of dipole-dipole
interacting atoms in optical lattices.
Phys. Rev. Lett. 90,
250404 (2002) (4
pages) (e-print quant-ph/0305107).
Abstract:
We propose and investigate a realization of the position- and
momentum-correlated Einstein-Podolsky-Rosen (EPR)
states
[Phys. Rev. 47, 777 (1935)] that have hitherto
eluded
detection. The realization involves atom pairs that are
confined
to adjacent sites of two mutually shifted optical lattices
and are
entangled via laser-induced dipole-dipole
interactions.
The EPR "paradox'' with translational variables is then
modified
by lattice-diffraction effects, and can be verified to a high
degree of accuracy in this scheme.
- S.F.
Hanna, W.D. Kulatilaka,
Z. Arp, T. Opatrny, M.O. Scully, J. P. Kuehner, and R.P. Lucht
Electronic-resonance-enhanced
coherent anti-Stokes Raman
spectroscopy of nitric oxide.
Applied Physics Letters 83,
1887-1889 (2003).
Abstract:
A dual pump, electronic-resonance-enhanced coherent anti-Stokes Raman
spectroscopy (CARS) technique for the measurement of minor species
concentrations has been demonstrated. The frequency difference between
a
visible Raman pump beam and Stokes beam is tuned to a vibrational
Q-branch Raman resonance of nitric oxide (NO) to create a Raman
polarization in the medium. The second pump beam is tuned into
resonance
with rotational transitions in the (1,0) band of the A2Sigma+-X2Pi
electronic transition at 236 nm, and the CARS signal is thus resonant
with transitions in the (0,0) band. We observe significant resonant
enhancement of the NO CARS signal and have obtained good agreement
between calculated and experimental spectra.
-
G. Beadie, J. Reintjes, M.
Bashkansky, T. Opatrny, and M.O. Scully,
Towards a FAST-CARS anthrax
detector: CARS generation in a DPA
surrogate molecule.
J. Mod. Optics 50, 2361-2368 (2003)
Abstract:
Coherent anti-Stokes Raman spectroscopy (CARS) has been investigated as
a detection method for the identification of dipicolinic acid (DPA), a
marker molecule for bacterial spores of anthrax. The laser dye molecule
DCM was used as a surrogate molecule for DPA. In preliminary
experiments, a molecular sensitivity was achieved in DCM that is
projected to be sufficient to detect the DPA in bacterial spore clumps
as small as 5.5 micrometer in diameter, small enough to be of interest
in practical detection scenarios .
- A.A.
Kolomenskii, S.N.
Jerebtsov, T. Opatrny, H.A. Schuessler, and M.O. Scully,
Spontaneous Raman spectra of
dipicolinic acid in microcrystalline
form.
J. Mod. Optics 50,
2369-2374 (2003).
Abstract:
Dipicolinic acid (DPA) is an important component of bacterial spores.
The Raman spectrum of DPA in the form of compacted powder was measured
in reflection at room temperature with excitation by a nanosecond laser
at 532 nm. The spectrum presents a set of characteristic frequency
bands
in the region 700-3090 cm-1 that
were identified with
characteristic vibrational modes of the DPA molecule.
- T.
Opatrny, N. Korolkova,
and G. Leuchs,
Mode structure and photon
number correlations in squeezed quantum
pulses.
Phys. Rev. A 66, 053813 (2002) (14
pages)
(e-print quant-ph/0204131).
Abstract:
The question of an efficient multimode description of optical pulses is
studied. We show that a relatively very small number of
nonmonochromatic
modes can be sufficient for a complete quantum description of pulses
with Gaussian quadrature statistics. For example, a three-mode
description was enough to reproduce the experimental data of photon
number correlations in optical solitons [S. Spälter, N.
Korolkova,
F. König, A. Sizmann, and G. Leuchs, Phys. Rev. Lett. 81, 786
(1998)]. This approach is very useful for a detailed understanding of
squeezing properties of soliton pulses with the main potential for
quantum communication with continuous variables. We show how homodyne
detection and/or measurements of photon number correlations can be used
to determine the quantum state of the multimode field. We also discuss
a possible way of physical separation of the nonmonochromatic modes.
- G.
Kurizki, A.G.
Kofman, D. Petrosyan, and T. Opatrný,
Control of molecular
decoherence and entanglement.
J. Opt. B: Quantum Semiclass. Opt. 4,
S294-S299 (2002).
Abstract:
The impediment towards the successful development of the field of
quantum information (QI) is decoherence, i.e., the loss of entanglement
by the effect of the environment on the systems of interest. An
important challenge is that of QI engineering, by entanglement and
decoherence control, in complex systems, such as unimolecular and
bimolecular systems, that can simultaneously handle large amounts of
QI.
Progress towards this goal can be achieved by: (a) decay modification
and decoherence suppression in molecules, using laser-induced phase and
amplitude modulation of rovibrational levels and inter-mode couplings;
(b) transfer of internal-translational entanglement and teleportation
of wavepackets via molecular dissociation and collisions.
- G.
Kurizki, D. Petrosyan,
T. Opatrny, M. Blaauboer, and B. Malomed,
Self-induced transparency and
giant nonlinearity in doped photonic
crystals.
J. Opt. Soc. Am. B-Optical Physics19,
2066-2074, (2002) (e-print quant-ph/0204076).
Abstract:
Photonic crystals doped with resonant atoms allow for uniquely
advantageous nonlinear modes of optical propagation. The first type of
mode is self-induced transparency (SIT) solitons and multidimensional
localized bullets propagating at photonic-bandgap frequencies. Such
modes can exist even at ultraweak intensities (few photons) and
therefore differ substantially either from solitons in Kerr-nonlinear
photonic crystals or from SIT solitons in uniform media. The second
type
of mode is cross coupling between pulses exhibiting electromagnetically
induced transparency and SIT gap solitons. We
show that extremely strong correlations (giant cross-phase modulation)
can be formed between the two pulses. These features may find
applications in high-fidelity classical and quantum optical
communications.
- T.
Opatrny and M.O.
Scully,
Enhancing Otto-mobile
efficiency via addition of a quantum Carnot
cycle.
Fortschritte der Physik 50,
657-663 (2002).
Abstract:
It was shown recently that one can improve the efficiency of the Otto
cycle by taking advantage of the internal degrees of freedom of an
ideal
gas [M. O. Scully, The Quantum Afterburner, Phys. Rev. Lett., to be
published]. Here we discuss the limiting improvement of the efficiency
by considering reversible cycles with both internal and external
degrees
of freedom.
- M.
O. Scully, G. W.
Kattawar, R. P. Lucht, T. Opatrný, H. Pilloff, A. Rebane, A.
V.
Sokolov, and M. S. Zubairy,
FAST CARS: Engineering a
laser spectroscopic technique for rapid
identification of bacterial spores.
Proc. Natl. Acad. Sci. USA 99,
10994-11001 (2002)
(e-print physics/0203007).
Abstract:
Airborne contaminants, e.g., bacterial spores, are usually analyzed by
time-consuming microscopic, chemical, and biological assays. Current
research into real-time laser spectroscopic detectors of such
contaminants is based on e.g., resonance fluorescence. The present
approach derives from recent experiments in which atoms and molecules
are prepared by one (or more) coherent laser(s) and probed by another
set of lasers. However, generating and using maximally coherent
oscillation in macromolecules having an enormous number of degrees of
freedom is challenging. In particular, the short dephasing times and
rapid internal conversion rates are major obstacles. However, adiabatic
fast passage techniques and the ability to generate combs of
phase-coherent femtosecond pulses provide tools for the generation and
utilization of maximal quantum coherence in large molecules and
biopolymers. We call this technique FAST CARS (femtosecond adaptive
spectroscopic techniques for coherent anti-Stokes Raman spectroscopy),
and the present article proposes and analyses ways in which it could be
used to rapidly identify preselected molecules in real time.
(2001)
- T.
Opatrny and D.-G. Welsch,
Coupled cavities for
enhancing the cross-phase modulationin
electromagnetically induced transparency.
Phys. Rev. A 64, 023805 (2001) (9
pages)
(e-print quant-ph/0012073).
Abstract:
We propose an optical double-cavity resonator whose response
to a
signal is similar to that of an Electromagnetically Induced
Transparency
(EIT) medium. A combination of such a device with a four-level EIT
medium can serve for achieving large cross-Kerr modulation of a probe
field by a signal field. This would offer the possibility of building a
quantum logic gate based on photonic qubits. We discuss the technical
requirements that are necessary for realizing a probe-photon phase
shift of Pi caused by a single-photon signal. The main difficulty is
the requirement of an ultra-low reflectivity beamsplitter and to
operate a sufficiently dense cool EIT medium in a cavity.
- T.
Opatrny and G. Kurizki,
Matter-wave entanglement and
teleportation by molecular
dissociation and collisions.
Phys. Rev. Lett. 86,
3180-3183 (2001) (e-print quant-ph/0009121).
Abstract:
We propose dissociation of cold diatomic molecules as a source of atom
pairs with highly correlated (entangled) positions and momenta,
approximating the original quantum state introduced by Einstein,
Podolsky and Rosen (EPR) [Phys. Rev. 47, 777 (1935)]. Wavepacket
teleportation is shown to be achievable by its collision with one of
the
EPR correlated atoms and manipulation of the other atom in the pair.
- A.G.
Kofman, G. Kurizki,
and T. Opatrny,
Zeno and anti-Zeno effects
for photon polarization dephasing.
Phys. Rev. A 63,
042108 (2001) (11
pages) (e-print quant-ph/0011077).
Abstract:
We discuss a simple, experimentally feasible scheme, which elucidates
the principles of controlling ("engineering") the reservoir spectrum
and
the spectral broadening incurred by repeated measurements. This control
can yield either the inhibition (Zeno effect) or the acceleration
(anti-Zeno effect) of the quasi-exponential decay of the observed state
by means of frequent measurements. In the discussed scheme, a photon is
bouncing back and forth between two perfect mirrors, each time passing
a
polarization rotator. The horizontal and vertical polarizations can be
viewed as analogs of an excited and a ground state of a two level
system (TLS). A polarization beam splitter and an absorber for the
vertically polarized photon are inserted between the mirrors, and
effect
measurements of the polarization. The polarization angle acquired in
the electrooptic polarization rotator can fluctuate randomly, e.g., via
noisy modulation. In the absence of an absorber the polarization
randomization corresponds to TLS decay into an infinite-temperature
reservoir. The non-Markovian nature of the decay stems from the many
round-trips required for the randomization. We consider the influence
of the polarization measurements by the absorber on this non-Markovian
decay, and develop a theory of the Zeno and anti-Zeno effects in this
system.
- T.
Opatrný and
D.-G. Welsch,
Cross Phase Modulation
Enhancement by Coupled Cavities and
Electromagnetically Induced Transparency.
8-th Central-European
Workshop on Quantum Optics (Prague
2001), in: Fortschritte der Physik 49,
1065-1070 (2001).
Abstract:
We propose an optical double-cavity resonator whose response to a
signal is similar to that observed in electromagnetically induced
transparency (EIT). A combination of such a device with a four-level
EIT
medium can serve for achieving large cross-Kerr modulation of a probe
field by a signal field.
- S.
Scheel, D.-G.
Welsch, and T. Opatrný,
Quantum Teleportation in
Noisy Environments.
8-th Central-European
Workshop on Quantum Optics (Prague
2001), in: Fortschritte der Physik 49,
1089-1094 (2001).
Abstract:
Teleportation of an unknown quantum state is an interesting issue in
quantum information processing. Unit fidelity is achieved if sender and
receiver share a maximally entangled state corresponding to the Hilbert
space of the quantum state to be teleported. Realistic experiments
necessarily make use of passive optical devices such as beam splitters
and optical fibers which show losses. Losses however, are known to
degrade the entanglement content, and hence the teleportation fidelity,
of any given quantum state. This is due to the interaction with a noisy
environment, say, an optical fiber. We combine two methods,
multiparticle entanglement and appropriate filtering, to restore some
of
the entanglement lost during the transmission process. The filtering
parameter and the basis used in the projective measurement of the
multiparticle-entangled state can be optimized for given material
properties (refractive index, fiber length).
- S.
Scheel, T.
Opatrný, and D.-G. Welsch,
Entanglement degradation of a
two-mode squeezed vacuum in
absorbing and amplifying optical fibers.
Optics and Spectroscopy 91,
411-417 (2001).
Abstract:
Applying the recently developed formalism of quantum-state
transformation of light at absorbing dielectric four-port devices [5],
we calculate the quantum state of the outgoing modes of a two-mode
squeezed vacuum transmitted through optical fibers of given extinction
coefficients. Using the Peres-Horodecki separability criterion for
continuous variable systems [4], we then compute both the maximal
length
of transmission of a two-mode squeezed vacuum through an absorbing
system for which the transmitted state is still inseparable and the
maximal gain for which inseparability can be observed in an amplifying
setup. Finally, we estimate an upper bound of the entanglement
preserved after transmission through an absorbing system. The results
show that the characteristic length of entanglement degradation
drastically decreases with increasing strength of squeezing.
- T.
Opatrny,
Homodyne detection and
quantum information.
Coherence and Statistics of Photons and Atoms", Ed. :J.
Perina
(John Wiley
& Sons, 2001), pp. 159-197.
Review article
- G.
Kurizki, A.E. Kozhekin,
T. Opatrny, and B. Malomed
Optical solitons in periodic
media with resonant and off-resonant
nonlinearities.
Progress in Optics, vol. 42, Ed. E. Wolf (North-Holland,
Amsterdam
2001), pp. 93-146. (e-print nlin.PS/0007007).
Abstract:
The properties of optical solitons in periodic nonlinear media are
reviewed. The emphasis is on solitons in periodically refractive media
(Bragg gratings) incorporating a periodic set of thin layers of
two-level systems resonantly interacting with the field. Such media
support a variety of bright and dark `gap solitons' propagating in the
band gaps of the Bragg gratings, as well as their multi - dimensional
analogs (light bullets).These novel gap solitons differ substantially
from their counterparts in periodic media with either cubic or
quadratic
off-resonant nonlinearities.
(2000)
- T.
Opatrny and G. Kurizki,
On the Possibility of Quantum
Computation Based on Photon Exchange
Interactions.
Fortschritte der Physik 48,
1125-1131 (2000). [Special
Issue on Experimental Proposals for Quantum Computation, Eds. S. L.
Braunstein and Hoi-Kwong Lo]
Abstract:
We examine several proposed schemes by Franson et al. for quantum logic
gates based on non-local exchange interactions between two photons in a
medium. In these schemes the presence of a single photon in a given
mode
is supposed to induce a large phase shift on another photon propagating
in the same medium. We conclude that the schemes proposed so far are
not
able to produce the required conditional phase shift, even though the
proposals contain many stimulating and intriguing ideas.
- S.
Scheel, L. Knöll, T.
Opatrny, and D.-G. Welsch,
Entanglement transformation
at absorbing and amplifying four-port
devices.
Phys. Rev. A 62,
043803 (2000) (11 pages) . (e-print quant-ph/0004003)
Abstract:
Dielectric four-port devices play an important role in optical quantum
information processing. Since for causality reasons the permittivity is
a complex function of frequency, dielectrics are typical examples of
noisy quantum channels, which cannot preserve quantum coherence. To
study the effects of quantum decoherence, we start from the quantized
electromagnetic field in an arbitrary Kramers-Kronig dielectric of
given
complex permittivity and construct the transformation relating the
output quantum state to the input quantum state, without placing
restrictions on the frequency. We apply the formalism to some typical
examples in quantum communication. In particular we show that for
Fock-entangled qubits the Bell-basis states |Psi> are more
robust
against decoherence than the states |Phi>.
- J.
Clausen, T. Opatrny, and
D.-G. Welsch,
Conditional teleportation
using optical squeezers and photon
counting.
Phys. Rev. A 62,
042308 (2000) (5 pages). (e-print quant-ph/0003142).
Abstract:
We suggest a scheme of conditional teleportation of quantum states of
optical fields using squeezers and photon counting. Alice feeds the
mode
whose state is desired to be teleported and one mode of a two-mode
squeezed vacuum into a parametric amplifier and detects output photon
numbers. The result is then communicated to Bob who shifts the photon
number of his part accordingly. We show that for some classes
of
states the method can yield, with reasonable success probability,
a teleportation fidelity close to unity. The method
represents a
modification of a recently proposed scheme [G.J. Milburn and
S.L.
Braunstein, Phys. Rev. A 60,
937 (1999)], where
measurements of the photon-number difference and the phase
sum are
considered. The present scheme brings the method closer to the current
experimental techniques.
- T.
Opatrny, J. Clausen,
D.-G. Welsch, and G. Kurizki
Squeezed-vacuum assisted
quantum teleportation.
7- th Central-European Workshop
on Quantum Optics (Balatonfured
2000), in: Acta Physica Slovaca, 50,
341-350 (2000).
Abstract:
We show that the fidelity of teleportation of continuous quantum
variables can be improved by conditional photon-number measurement of
the entangled state. Further, we propose a teleportation scheme based
on
photon counting on the output fields of a squeezer that combines the
mode whose quantum state is desired to be teleported and one mode of
the
two-mode squeezed vacuum playing the role of the entangled state.
- S.
Scheel, L. Knöll, T.
Opatrný, D.-G.Welsch
Entanglement transformation
at absorbing and amplifying dielectric
four-port devices.
7- th Central-European Workshop
on Quantum Optics (Balatonfured
2000), in: Acta Physica Slovaca, 50,
351-358 (2000).
Abstract:
Dielectric four-port devices play an important role in optical quantum
information processing. Since for causality reasons the permittivity is
a complex function of frequency, dielectrics are typical examples of
noisy quantum channels, which prevent them from preserving quantum
coherence. To study the effects of quantum decoherence, we start from
the quantized electromagnetic field in an arbitrary Kramers-Kronig
dielectric of given complex permittivity and construct the
transformation that relates at a four-port device the output quantum
state to the input quantum state, without placing restrictions on the
frequency. Basing on the relative entropy as an entanglement measure,
we
apply the formalism to the transformation of entanglement, with special
emphasis on the entanglement degradation in absorbing optical fibers.
In particular we show that the Bell basis states |Psi>
using
Fock states are more robust against decoherence than the states
|Phi>.
- J.
Fiurasek, M. Dakna, T.
Opatrny, and D.-G. Welsch
Sampling the canonical phase
from phase-space functions.
Phys. Rev. A 62,
063811 (2000) (10 pages)
(e-print quant-ph/0004059).
Abstract:
We discuss the possibility of sampling exponential moments of the
canonical phase from the s-parametrized phase space functions. We show
that the sampling kernels exist and are well-behaved for any
s>-1, whereas for s=-1 the kernels diverge in the origin. In
spite of
that we show that the phase space moments can be sampled with any
predefined accuracy from the Q-function measured in the double-homodyne
scheme with perfect detectors. We discuss the effect of imperfect
detection and address sampling schemes using other measurable
phase-space functions. Finally, we discuss the problem of sampling the
canonical phase distribution itself.
- T.
Opatrny, G. Kurizki,
and D.-G. Welsch,
Improvement on teleportation
of continuous variables by photon
subtraction via conditional measurement.
Phys. Rev. A 61,
032302 (2000) (7 pages).
Abstract:
We show that the recently proposed scheme of teleportation of
continuous variables [S.L. Braunstein and H.J. Kimble, Phys. Rev. Lett.
80, 869 (1998)] can be improved by a conditional measurement of the
entangled state shared by the sender and the recipient. The conditional
measurement subtracts photons from the original entangled two-mode
squeezed vacuum, by transmitting each mode through a low-reflectivity
beam splitter and performing a joint photon-number measurement on the
reflected beams. In this way the degree of entanglement of the shared
state is increased and so is the fidelity of the teleported state.
(1999)
- D.-G.
Welsch, W. Vogel and T.
Opatrny,
Homodyne detection and
quantum state reconstruction.
Progress in Optics, vol. XXXIX, ed. E. Wolf (North-Holland, Amsterdam),
63-210 (1999).
Review article
- T.
Opatrny and G. Kurizki,
Optimization approach to
entanglement distillation.
Phys. Rev. A 60,
167-172 (1999).
Abstract:
We put forward a method for optimized distillation of partly
entangled pairs of qubits into a smaller number of more entangled pairs
by recurrent local unitary operations and projections. Optimized
distillation is achieved by minimization of a cost function with up to
30 real parameters, which is chosen to be sensitive to the fidelity and
the projection probability at each step. We show that in many cases
this
approach can significantly improve the distillation efficiency in
comparison to the present methods.
- T.
Opatrny, B.A. Malomed, and G.
Kurizki,
Dark and bright solitons in
resonantly absorbing gratings.
Phys. Rev. E 60,
6137-6149 (1999).
Abstract:
We consider an optical medium consisting of a periodic
refractive-index grating and a periodic set of thin layers of two-level
systems resonantly interacting with the electromagnetic field.
Recently,
it has been shown that such a system gives rise to a vast variety of
stable bright solitons. In this work, we demonstrate that the system
has another very unusual property: stable bright solitons can
coexist with stable continuous-wave (cw) states and stable dark
solitons (DS's). Depending on the parameters' values, a DS
frequency band coexists (without overlap) with one or two
bright-soliton
bands. Quiescent (standing) DS's are found in an analytical form, and
moving ones are obtained numerically. Simulations show that a
considerable part of the DS solutions are completely stable against
arbitrary small perturbations. The fact that this system supports both
stable bright and
dark solitons for the same
parameters' values may find interesting applications in photonics.
(1998)
- T.
Opatrny, M. Dakna and D.-G.
Welsch,
Number-phase uncertainty
relations: verification by homodyning.
Phys. Rev. A.57,
2129-2133 (1998).
Abstract:
It is shown that fundamental uncertainty relations between photon
number and canonical phase of a single-mode optical field can be
verified by means of a balanced homodyne measurement. All the relevant
quantities can be sampled directly from the measured phase-dependent
quadrature distribution.
- M.
Dakna, T. Opatrny and D.-G.
Welsch,
Homodyne measurement of
exponential phase moments.
Optics Commun.148,
355-375 (1998) .
Abstract:
It is shown that the exponential moments of the canonical phase can be
directly sampled from the data recorded in
balanced homodyne detection. Analytical expressions for the sampling
functions are derived, which are valid for arbitrary
states and bridge the gap between quantum and classical phase. The
reconstruction of the canonical phase distribution from
the experimentally determined exponential moments is discussed.
- T.
Opatrny, M. Dakna and D.-G.
Welsch,
Exponential moments of
canonical phase: homodyne measurements.
5- th International Conference
on Squeezed States and Uncertainty
Relations (Balatonfured,
Hungary, 1997) Proceedings:
NASA/CP-1998-206855, pp. 621-626 (1998).
Abstract:
A method for direct sampling of the exponential
moments of canonical phase from the data recorded
in
balanced homodyne detection is presented. Analytical expressions for
the
sampling functions are shown which are valid for arbitrary states. A
numerical simulation illustrates the applicability of the method and
compares it with the direct measurement of phase by means of double
homodyning.
- D.-G.
Welsch, M. Dakna, L.
Knöll and T. Opatrny,
Photon adding and subtracting
and Schroedinger-cat generation in
conditional output measurement on a beam splitter.
5- th International Conference
on Squeezed States and Uncertainty
Relations (Balatonfured,
Hungary, 1997) Proceedings:
NASA/CP-1998-206855, pp. 609-614 (1998).
Abstract:
The problem of photon adding and subtracting is studied, using
conditional output measurement on a beam splitter. It is shown that for
various classes of states the corresponding photon-added and
-subtracted
states can be prepared. Analytical results are presented, with special
emphasis on photon-added and -subtracted squeezed vacuum states, which
are found to represent two different types of Schroedinger-cat-like
states. Effects of realistic photocounting and Fock-state preparation
are discussed.
- M.
Dakna, G. Breitenbach, J.
Mlynek, T. Opatrny, S. Schiller and D.-G. Welsch,
Homodyne measurement of
exponential phase momenta for
quantum-phase reconstruction.
Optics Commun.152,
289-292 (1998) .
Abstract:
We directly sample the exponential momenta of the canonical phase for
various quantum states from the homodyne output.
The method enables us to study the phase properties experimentally,
without making the detour via reconstructing the
density matrix or the Wigner function and calculating the phase
statistics from them. In particular, combing the
measurement with a measurement of the photon-number variance, we verify
fundamental number-phase uncertainty.
(1997)
- A. Miranowicz, T.
Opatrny and J. Bajer,
Harmonic oscillator states in
finite dimensional Hilbert space.
In: T. Hakioglu and A.S. Shumovsky (eds.), Quantum Optics and the
Spectroscopy of Solids, pp. 225-236 (Kluwer, 1997).
- T.
Opatrny, D.-G. Welsch and W.
Vogel,
Multi-mode density matrices
of light via amplitude and phase
control.
Optics Communications 134,
112-116 (1997).
Abstract:
A new method is described for determining the quantum state of
correlated multimode radiation by interfering the modes and measuring
the statistics of the superimposed fields in four-port balanced
homodyne
detection. The full information on the N-mode quantum state is obtained
by controlling both the relative amplitudes and the phases of the
modes, which simplifies the reconstruction of density matrices to only
N+1 Fourier transforms. In particular, this method yields
time-correlated multimode density matrices of optical pulses by
superimposing the signal by a sequence of short local-oscillator
pulses.
- T.
Opatrny, D.-G. Welsch and W.
Vogel,
Homodyne detection for
measuring internal quantum correlations of
optical pulses.
Phys. Rev. A 55,
1416-1422 (1997).
Abstract:
A method is described for determining the quantum
correlations at
different times in optical pulses by using balanced homodyne detection.
The signal pulse and sequences of ultrashort test pulses (local
oscillators) are superimposed, where for chosen distances between the
test pulses their relative phases and intensities are varied from
measurement to measurement. The correlation statistics of the signal
pulse is obtained from the time-integrated difference photocurrents
measured.
- T.
Opatrny and D.-G. Welsch,
Density-matrix reconstruction
by unbalanced homodyning.
Phys. Rev. A 55,
1462-1465 (1997).
Abstract:
Recently a method for measuring quasidistributions of single-mode
optical fields in unbalanced homodyne detection has been proposed [S.
Wallentowitz and W. Vogel, Phys. Rev. A 53,
4528 (1996);
K. Banaszek and K. Wodkiewicz, Phys. Rev. Lett. 76,
4344
(1996)]. We show that the scheme can be used for direct sampling of the
signal-mode density matrix in the Fock basis. In this case it is
sufficient to vary only the phase of the local oscillator keeping its
amplitude constant.
- M.
Dakna, T. Anhut, T. Opatrny, L.
Knöll and D.-G. Welsch,
Schroedinger cat-like states
by conditional measurements on a
beam-splitter.
Phys. Rev. A 55,
3184-3194 (1997).
Abstract:
A scheme for generating Schroedinger cat-like states of a single mode
optical field by means of conditional measurement is proposed. A
squeezed vacuum state is mixed on a beam splitter with a vacuum state
and photons are counted in one of the outputs. The conditional state in
the other output has properties very similar to those of the
superposition of two coherent states with opposite phases. We present
analytical formulas for the Fock representation, the Wigner and Husimi
functions, and for the quadrature distributions of these states. We
also
discuss the effect of realistic counting of the photons.
- T.
Opatrny, D.-G. Welsch, S.
Wallentowitz and W. Vogel,
Quantum state reconstruction
by multichannel unbalanced homodyning.
J. Mod. Optics 44,
2405-2425 (1997).
Abstract:
Multichannel unbalanced homodyning is proposed for measuring
the density matrix of a single-mode optical field
in the
photon-number representation. Combining the signal
beam and
the local oscillator by a high-transmittance beam
splitter,
the interfering field is detected using
multichannel
photocounting. The density matrix is determined by
direct
statistical sampling of the coincident events
recorded for
various values of the local-oscillator phase. The
usefulness
of the method is demonstrated by computer
simulations of
measurements including error estimations.
- T.
Opatrny, D.-G. Welsch and W.
Vogel,
Least-squares inversion for
density-matrix reconstruction.
Phys. Rev. A 56,
1788 (1997).
Abstract:
We propose a method for reconstruction of the density matrix from
measurable time-dependent (probability) distributions of physical
quantities. The applicability of the method based on least-squares
inversion is - compared with other methods - very universal. It can be
used to reconstruct quantum states of various systems, such as harmonic
and and anharmonic oscillators including molecular vibrations in
vibronic transitions and damped motion. It also enables one to take
into
account various specific features of experiments, such as limited sets
of data and data smearing owing to limited resolution. To illustrate
the method, we consider a Morse oscillator and give a comparison with
other state-reconstruction methods suggested recently.
- T.
Opatrny, W. Vogel and D.-G.
Welsch,
Quantum-state reconstruction
for damped systems.
5- th Central-European Workshop
on Quantum Optics (Praha 1997),
in: Acta Physica Slovaca, 47,
327-330 (1997).
Abstract:
It is shown that least-squared inversion is a suitable method for
reconstructing the density matrix from measurable time-dependent
quantities. It enables one to take into account various specific
features of experiments, such as limited sets of data and data smearing
owing to limited resolution. The method can be used to reconstruct the
quantum state of various systems, such as harmonic and anharmonic
oscillators including molecular vibrations in vibronic transitions and
damped motion. To illustrate it, we consider the reconstruction of the
density matrix of a damped harmonic oscillator.
- M.
Dakna, T. Opatrny, L.
Knöll and D.-G. Welsch,
Conditional Schroedinger-cat
output states of a beam splitter.
5- th Central-European Workshop
on Quantum Optics (Praha 1997),
in: Acta Physica Slovaca, 47,
267-272 (1997).
Abstract:
We show that when a squeezed vacuum and an ordinary vacuum are combined
by a beam splitter and in one of the output channels the number of
photons is measured, then conditional quantum states in the other
output
channel can be obtained which reveal all the properties of
superpositions of macroscopically distinguishable states. The component
states are very close to squeezed coherent states and approach coherent
states for sufficiently large numbers of detected photons. We also
consider the problem of producing the superposition states under the
conditions of realistic photocounting, assuming multichannel detection
with highly efficient avalanche photodiodes. We show that for properly
chosen parameters quantum interferences can still be found even for a
realistic arrangement of detectors.
(1996)
- T.
Opatrny, A. Miranowicz and J.
Bajer,
Coherent states in
finite-dimensional Hilbert space and their
Wigner representation.
J. Mod. Opt. 43,
417-432 (1996).
Abstract:
We consider two definitions of coherent states in a finite-dimensional
Hilbert space based on (i) truncation of the usual coherent state
expansion and (ii) generalization of the displacement operator acting
on
vacuum. The number-phase Wigner function is computed for such states.
Analytical results and numerically computed graphs are presented.
Special attention is paid to two-level states and to their Stokes
parameter representations.
- T.
Opatrny, D.-G. Welsch and V.
Buzek,
Parametrized discrete
phase-space functions.
Phys. Rev. A 53,
3822-3835 (1996).
Abstract:
Using discrete displacement-operator expansion, s-parametrized
phase-space functions associated with the operators in a finite
dimensional Hilbert space are introduced and their properties are
studied. In particular, the phase-space functions associated with the
density operator can be regarded as quasidistributions whose properties
are similar to those of the well-known quasidistributions in the
continuous phase space. So the Q-function (s=-1) is non-negative and
can
be measured directly in particular experiments, whereas the P-function
(s=1) corresponds to the diagonal form of the density operator in an
overcomplete basis. Except of the W-function (s=0), the introduction of
discrete phase-space functions requires the choice of a special
reference state. We finally present a simple model for measuring the
discrete Q-function.
- Z.
Hradil, R. Myska, T. Opatrny
and J. Bajer,
Entropy of phase measurement:
Quantum phase via quadrature
measurement.
Phys. Rev. A 53,
3738-3742 (1996).
Abstract:
The content of phase information of an arbitrary phase-sensitive
measurement is evaluated using the maximum likelihood estimation. The
phase distribution is characterized by the relative entropy-a nonlinear
functional of input quantum state. As an explicit example, the multiple
measurement of the quadrature operator is interpreted as quantum phase
detection achieving the ultimate resolution predicted by the Fisher
information.
- V.
Majernik and T. Opatrny,
Entropic uncertainty
relations for a quantum oscillator.
J. Phys. A: Math. Gen. 29,
2187-2197 (1996).
Abstract:
We calculated the Shannon entropy of position and momentum for the
stationary quantum states of the harmonic oscillator as a function of
its energy and determined the corresponding entropic uncertainty
relations for them. We found an approximate phenomenological function
for the dependence of position and momentum entropies on the large
quantum numbers and the corresponding asymptotic entropy - energy
relation for the stationary harmonic oscillator. We also studied the
time evolution of the position and momentum entropies of the
non-stationary harmonic oscillator for the coherent states, squeezed
vacuum and Schrödinger cat states.
- T.
Opatrny, D.-G. Welsch and W.
Vogel,
Quantum state measurement of
multimode light pulses.
4 th Central-European Workshop
on Quantum Optics (Budmerice,
1996), in: Acta Physica Slovaca 46,
469-474 (1996).
Abstract:
A method for measuring internal quantum correlations and
multimode density matrices of optical pulses is proposed. In
balanced homodyne detection a signal pulse and sequences of
short
local-oscillator pulses are superimposed and the
time-integrated
difference-count statistics is recoreded. For chosen
distances
between the test pulses, the phases and relative intensities
of
the pulses are varied from measurement to measurement. Using
a
sequence of N test pulses, the quantum statistics of the
signal
pulse can then be obtained in terms of N correlated
nonmonochromatic modes. In particular, the determination of
the
N-mode density matrix in a field-strength basis can be
accomplished with (N +1) Fourier integrals. The method also
applies to the measurement of the quantum state of a correlated N-mode
field whose modes are separable. In this case
pre-superimposed
signal-field modes must be combined with a local-oscillator mode.
(1995) - T.
Opatrny, V. Buzek, J. Bajer and G. Drobny,
Propensities in discrete
phase-spaces: Q-function of a state in a
finite-dimensional Hilbert space.
Phys. Rev. A 52,
2419-2428 (1995).
Abstract:
We present a Q function of a state of a quantum-mechanical system in a
finite-dimensional Hilbert space. This discrete Q function is defined
with the help of the Wódkiewicz concept of propensities,
i.e., we
define the Q function as a discrete convolution of two Wigner functions
based on Wootter's formalism, one of the state itself and one of the
filter state. The discrete Q function takes nonnegative values in all
``points'' of the discrete phase space and is normalized and it is
possible to reconstruct from it the density operator of the state under
consideration. We analyze Q-function graphs for several states of
interest.
- T.
Opatrny,
Number - phase uncertainty
relations.
J. Phys. A: Math. Gen. 28,
6961-6975 (1995).
Abstract:
The minimization problem of finding the number-phase minimum
uncertainty states (MUS) is considered and its solutions are
found
either numerically or, under some special conditions, analytically. The
phase uncertainty measure is based on the Bandilla - Paul dispersion.
The problem is treated (i) in a finite dimensional Hilbert space and
(ii) for a countably-infinite dimensional Hilbert space (i.e. the
standard quantum harmonic oscillator), with the constraint of
a
given mean photon number. The MUS relations between the photon number
uncertainty and phase uncertainty are presented. Connections to some
other minimization problems are discussed.
- A. Miranowicz, K.
Piatek, T. Opatrny and R. Tanas,
Phase coherent states.
3 rd Central-European Workshop
on Quantum Optics (Budmerice,
1995), in: Acta Physica Slovaca 45,
391-394 (1995).
(1994) - J.
Bajer, T. Opatrny and J. Perina,
Photon statistics of higher
harmonics and subharmonics generation.
Quantum Optics 6,
403-410 (1994).
Abstract:
The quantum statistics of higher harmonics and subharmonics generation
processes is studied in an exact way. By means of the described
numerical way the Q-distributions and Wigner distributions are
calculated and presented. The non-classical effects are examined and
corresponding relations are derived.
- W.
C. Henneberger and T. Opatrny,
When is the wave function
single valued?
Int. J. Theor. Phys. 33,
1783-1795 (1994).
Abstract:
It is shown that single-valuedness of the wave function can be lost
because of an external field approximation. The Aharonov-Bohm effect is
studied in detail as an example of the problem. Specifically, it is
shown that the solenoid (represented as a rotating, charged cylinder)
has a wave function that undergoes a Phase shift equal in magnitude,
but
with opposite sign, to the phase shift suffered-by the electron's wave
function when the electron passes the solenoid.
- T.
Opatrny,
Mean value and uncertainty of
optical phase - a simple mechanical
analogy.
J. Phys. A: Math. Gen. 27,
7201-7208 (1994).
Abstract:
There exist several definitions of the mean value and the uncertainty
of phase of an optical field. We show that one of these definitions is
especially simple and intuitive because of its mechanical analogy. On
its basis, we also derive the summation rule and the Tchebyshev
inequality for random angular and phase variables and a number - phase
uncertainty relation.
(1993) - T.
Opatrny and J. Perina,
Non-image-forming
polarization optical devices and Lorentz
transformation - an analogy.
Phys. Lett. A 181,
199-202 (1993).
Abstract:
An analogy between optical field transformations and Lorentz
transformations is presented. Spatial rotations correspond to passive
optical elements which conserve the energy of the light beam, pure
boosts are represented by active elements with optically pumped media.