Omar Aguilar Loreto
Universidad de Guadalajara, Marcelino
García Barragán No.1421, Col. Olímpica,
C. P. 44420 Guadalajara,
Jal.
(Poster,Tu-17:30)
The
physical realization of three level atom tomography is presented. The
degenerate and non-degenerate cases of above systems are analyzed. In the
non-degenerate case, the reconstruction formula for density matrix, is found
and its physical implications are analyzed.
Ion traps in interaction with laser fields: a
RWA-free
perturbative approach
Paolo
Aniello
University
of Napoli Federico II, Napoli, Italy
Complesso Universitario di Monte S. Angelo, via Cintia,
80126
Napoli, ITALY
(Talk, Mo-18:00)
The Hamiltonian describing a single
ion placed in a potential trap in interaction with a laser beam is studied by
means of a suitable perturbative approach. It is shown, in particular, that the
rotating wave approximation does not provide the correct expression, at the
first perturbative order, of the evolution operator of the system.
Is there a lower bound energy in the harmonic
oscillator
interacting whit a heat bath?
L.M. Arévalo Aguilar1, N. G. de Almeida2,
and C. J. Villlas-Boas3
1CIO, Loma del Bosque No 115, Fracc.
Lomas del campestre, C. P. 37150, León, Gto.
2Universidade Católica de Goiás,3Universidade
Federal de São Carlos.
(Poster,Tu-17:30)
In this
contribution we investigate the lower bound energy of the usual Hamiltonian
employed in Quantum Optics to model the interaction between a harmonic
oscillator and a heat bath, i. e. the linear coupling model. We show that this
model have serious inconsistencies. In particular, it is showed that for this
Hamiltonian it is difficult to assign lower bound energy. Therefore, in this
model the harmonic oscillator behaves like a source of infinite energy, which
is a mislead result.
Quantum Interference and Decoherence of Complex
Molecules
Markus Arndt
Institut
für Experimentalphysik, Universität Wien
Boltzmanngasse 5, 1090 Wien, Austria
(Talk, Mo-11:30)
The
wave-particle duality of massive objects is
one of the corner stones of quantum physics. Nevertheless one does not
see any effect of this quantum property in our everyday world. Our current
experiments are aiming at exploring the limits to which one can still observe
the quantum wave-nature of massive objects and to understand the role of the
internal molecular temperature, structure,and symmetry. We discuss de Broglie
interference experiments with C70 where we reach temperatures in excess of 3000
K, with porphyrins which have a lower geometrical symmetry and with
C60F48 which represent the current mass record of 1632 amu in matter wave
interferometry. In addition to the importance of the internal properties we
investigate the influence of the coupling to the environment caused by
molecular collisions and thermal radiation.
The Wigner distribution function in the recovering of
coherence from two mutually spatially incoherent point sources
L.
R. Berriel-Valdos, S. Guel*, J.
Carranza G and J. L. Juárez-Pérez
Instituto
Nacional de Astrofísica, Óptica y Electrónica
L.
E. Erro #1, Tonantzintla. 72840 Puebla,
Instituto
de Investigaciones en Comunicaciones Ópticas
UASLP,
Av. Krakorun # 1740, Lomas 4ª sección. 78210 San Luis Potosí.
(Poster,
Tu-17:30)
The
resolution value given by the positiveness condition on the Wigner distribution
function is used to know when two mutually incoherent point sources are
separated. In this work it is analyzed the possibility to get coherence from
two incoherent sources starting from this resolution value and the result is
compared with the degree of coherence obtained by the resolution values
assigned by the Rayleigh and Sparrow criterion.
Vladislav N. Beskrovnyy and Mikhail I.
Kolobov
Laboratoire PhLAM, Université de
Lille 1, F-59655 Villeneuve d'Ascq Cedex, France
(Talk, Th-18 :30)
We numerically investigate the role of quantum fluctuations in
superresolution of optical objects. First, we confirm that when quantum
fluctuations are not taken into account, one can easily improve the
resolution by one order of magnitude beyond the diffraction limit. Then
we investigate the standard quantum limit of superresolution which is achieved
for illumination of an object by a light wave in a coherent state. We
demonstrate that this limit can be beyond the diffraction limit. Finally, we
show that further improvement of superresolution beyond the standard quantum
limit is possible using the object illumination by a multimode squeezed light.
ENTANGLEMENT
AND TELEPORTATION IN THE CONTINUOUS VARIABLE REGIME
Warwick
P. Bowen, Roman Schnabel, Nicolas Treps, Ben C.
Buchler, Tim C. Ralph, Hans-A. Bachor, Thomas Symul, and Ping Koy, Lam
The
Australian National University, Canberra, Australia
(Talk, Tu:15:30)
We discuss some methods
presently used to characterize entanglement and teleportation in the continuous
variable regime. We experimentally characterize the strength of
entanglement using the EPR [1] and Inseparability criteria [2], and demonstrate
qualitative differences in their dependence on loss [3]. We present
experimental teleportation results in both unity and non-unity gain regimes
[4], and analyze these results in terms of fidelity, signal transfer and
conditional variance (TV), and a new measure the gain normalized conditional
variance [5]. We show that this new measure is significant for
entanglement swapping procedures.
[1] M. D. Reid and P. D. Drummond, Phys.
Rev. Lett. 60, 2731 (1988).
[2] L-M. Duan, G. Giedke, J. I. Cirac and P. Zoller,
Phys. Rev. Lett. 84, 2722 (2000).
[3] W. P. Bowen, R. Schnabel, P. K. Lam, and T.
C. Ralph, Phys. Rev. Lett. 90, 043601 (2003).
[4] W. P. Bowen, N. Treps, B. C. Buchler, R.
Schnabel, T. C. Ralph, H.-A. Bachor, T. Symul, and P. K. Lam, Phys. Rev. A 67,
032302 (2003).
[5] W. P. Bowen, N. Treps, B. C. Buchler, R.
Schnabel, T. C. Ralph, T. Symul and P. K. Lam quant-ph/0303179
Many-body secret message sharing:
propose and security analysis of two protocols for
direct communication
Department
of Chemical Physics and Optics,Faculty of Mathematics and Physics
Charles
University, Ke Karlovu 3, 121 16 Prague 2, Czech Republic
Miloslav
Dusek
Department
of Optics, Palacký University, 17. listopadu 50, 772 00 Olomouc
Czech
Republic
(Poster, Tu-17:30)
Two
new protocols for secret information splitting among many participants are
proposed. One of them uses only two-partite entangled states (Bell states) and
the other one multi-partite entangled states. The security against the family of
rather general man-in-the-middle attacks is proved. Also the dependence of the
possibly leaked information about the message on the error rate caused by an
eavesdropping is discussed.
Entangled imaging in the macroscopic realm
E. Brambilla, A. Gatti, L.A.Lugiato and M.Bache
Dipartimento di Scienze, Università dell'Insubria, Via Valleggio 11, Como,
Italy
(Talk, Tu-12:30 )
We formulate a theory of entangled imaging
which includes also the case of a large number of photons in the entangled
beams. We analyze the problem on the basis of a compact imaging scheme which
allows to observe the object or the Fourier transform of the object. It turns
out that the results for imaging and the wave-particle duality fesatures, which
have been demonstrated in the microscopic case,persist in the macroscopic
domain. We discuss both the case of direct intensity detection and the case of
homodyne detection.
On the way from
flipping qubits to quantum programming
Vladimír
Bužek
Department
of Mathematical Physics, National University of Ireland, Maynooth, Co. Kildare,
Ireland
(Talk, Mo-8:50)
Conditional homodyne detection as a test of quantum versus
classical squeezing
Howard J.
Carmichael
Department of
Physics, University of Auckland, Private Bag 92019
Auckland, New
Zealand
(Talk, Mo-10:20)
The measurement of squeezing by the method of conditional homodyne
detection is discussed. It is shown that conditional detection distinguishes
qualitatively between vacuum state squeezing and squeezed classical noise.
Whereas conventional squeezed-light detection makes only a quantitative
distinction, based on the setting of the shot noise level, under conditional
detection, the measured correlation function changes shape in the presence of
classical noise. The ideas are illustrated by an example which treats the
generation and detection of squeezed thermal noise within the framework of the
quantum trajectory theory of cascaded open systems.
Octavio Castaños1,
Enrique López-Moreno2, and Ramón López-Peña1
1Instituto de Ciencias
Nucleares, UNAM, México D. F. 04510
2Facultad de Ciencias,
UNAM, México D. F. 04510
(Poster,
Tu-17:30)
At
the beginning of the nineties Kitagawa and Ueda proposed a new definition of squeezed
spin states where there are real correlations between individual elementary
spin states, besides of establishing two mechanisms to produce squeezing by
means of nonlinear interactions. In
this work we use the atomic coherent states together with the catastrophe
formalisms to establish the geometric properties of the mixing of the one-axis
twisting and two-axis countertwisting nonlinear spin interactions. We find the bifurcation and Maxwell sets of
the energy surface function, which are useful to establish the equilibrium
configurations and phase transitions. Finally we show its relevance to organize
the classical orbits and the structure of the quantum energy levels.
Hector M. Castro-Beltran, CIICAp-UAEM, Mexico
Gabriel Arroyo-Correa, INAOE, Mexico
(Poster, Tu-17:30)
We use quantum
trajectory theory to study the effect of spontaneous emission jumps to the ground state of a two-level atom
driven by a field of constant amplitude and detuning varying linearly in time,
the Landau-Zener model. The transient nature of this process makes it clear
that the stage at which the photon is emitted is critical for the subsequent evolution. We study both populations
and coherences of the levels, and illustrate
the atomic evolution in the Bloch sphere. We have obtained also analytical solutions for the non-normalized state
amplitudes in the time intervals between jumps.
SUB-POISSONIAN LIGHT
AT CONSECUTIVE NONLINEAR OPTICAL INTERACTIONS
Anatoly S. Chirkin
(Talk, Fr-12:00)
A quantum theory is developed of
optical parametric interaction at low-frequency pumping, which can be
implemented in nonlinear photonic crystals at consecutive interactions of light
waves with multiple frequencies. Basic
attention is paid to analysis of spatial dynamics of the mean photon number and
the Fano factor at signal and additional frequencies are analyzed. Photon
statistics is also studied for the
mentioned above frequencies.
Nonclassical light generation in the process
of self-frequency halving
in periodically poled active nonlinear crystals
Anatoly S. Chirkin, Alexey A. Novikov, Georgy D.
Laptev
(Poster, Tu-17:30)
We present the results of
analysis of quantum properties of light at self-frequency halving in periodically poled active nonlinear crystals
(PPACs). This process has two thresholds: the first threshold is due to
laser generation and the second one is connected with subharmonic generation.
One has obtained expressions for squeezing spectra which take into account both
nonlinear and laser properties of crystal and dynamics of polarization and
inverse population. The regimes of subharmonic generation below and above
threshold are considered. The calculations
have been carried out for periodically poled active nonlinear Nd:Mg:LiNbO3 crystal.
Conditional quantum dynamics with
multiple observers
Diego Dalvit
Los Alamos National Laboratory, USA
(Talk,
Mo-17:40)
We consider several observers
who monitor different parts of the environment of a single quantum system and use
their data to deduce its state. We derive a set of
stochastic conditional master equations that describe the evolution of the density matrices each observer ascribes to the system under the Markov approximation,
and show that this problem can be reduced
to the case of a single ``superobserver", who has access to of all the
acquired data. The key problem - consistency of the sets of data acquired by different observers - is then reduced to
the probability that a given
combination of
data sets will be ever detected by the ``superobserver". The
resulting conditional master equations are applied to several physical examples: homodyne detection of phonons in
quantum Brownian motion, photodetection and homodyne detection of resonance fluorescence from a two-level
atom. We introduce relative
purity to quantify the correlations between the information about the
system gathered by different observers from their measurements of the
environment. We find that observers gain the most information about the state of the system and they agree the most about
it
when they measure in the environment basis most closely correlated with the
optimally predictable pointer basis of the system.
CHARACTERIZATION AND ENGINEERING OF QUANTUM OPERATIONS.
Giacomo Mauro D'Ariano
University of Pavia, Italy
(Talk,
We-9:40)
When a quantum system enters a quantum device/apparatus, its state transforms
according to a linear, trace-non-increasing, and completely positive map, the
so-called ``Quantum Operation'' (QO), which describes the general conditioned dynamics through the device. In thisTalk we address
the problem of how to achieve a complete characterization of a QO, and how to discriminate
among a set of different QO's . We will see that there are special non-classical states that, when
used as input for the QO, carry a complete information about it.
Methods especially suited to measuring apparatuses are presented, and, as an application,
a scheme for an experimental absolute characterization of a photo-detector is proposed.
Connections with the problem of designing programmable QO devices are given in the concluding part.
QUANTUM MEASUREMENTS VIA UNIVERSAL DETECTORS
G. M. D'Ariano, P. Perinotti, and M. F. Sacchi
Quantum Optics & Information Group, Unita' INFM and
Dipartimento di Fisica "A. Volta'',
Universita' di Pavia, via A.
Bassi 6, I-27100 Pavia, Italy
(Talk,
We-12:20)
We address the problem of measuring the expectation value of an
arbitrary operator O via a universal detector, namely a measuring
apparatus that is independent of O. A universal detector acts on a composite
quantum system involving an ancilla, and provides the expectation values just
through a classical processing of the outcomes of the measurement. We
characterize such universal detectors, and show how Bell measurements
allow to construct them.
QUANTUM-STATE MEASUREMENT AND QUANTUM-CLASSICAL
TRANSITION IN PHASE SPACE
Luiz Davidovich, A.R.R. de Carvalho, F. Toscano e R.L. de Matos Filho
Instituto de Fisica, Universidade Federal do Rio de Janeiro
Cx. P. 68528, 21941-972 Rio de Janeiro, RJ, BRAZIL
(Talk, Fr-9:00)
We discuss the classical-quantum transition in phase space through the
time- dependent behavior of the Wigner function, which may be directly
measured for electromagnetic field in
cavities and trapped ions. We concentrate on the kicked harmonic oscillator, establishing bounds for the time at which
the
classical and quantum distributions differ markedly. These bounds depend on the
diffusion coefficient, the amplitude of the
kicks, and the Lamb-Dicke parameter. We show how
this model may be implemented with trapped ions, and discuss how the possibility of engineering different kinds of reservoir
leads
to a separation between the roles of dissipation and diffusion in the classical
limit of the system.
Fabio Dell'Anno
Department of Physics ''E. R. Caianiello'', University of Salerno,
Via S. Allende I-84081, Baronissi (SA), Italy.
(Talk, Th-18:10)
We introduce a nonlinear canonical two-mode transformation, generalizing
the standard Bogoliubov one. We derive model Hamiltonians for multiphoton
parametric processes, applying the nonlinear canonical formalism to the
macroscopic electrodynamic theory in nonlinear media. We define two-mode
multiphoton (non-gaussian) squeezed states and we analyze their entanglement
and correlation properties. At last, we investigate the experimental
feasibility of our models, through the interaction of classical pumps with
nonlinear crystals.
Contextual Realization of the
Universal Optimal Cloning and U-NOT Machines by Optical Parametric Amplification
Francesco De Martini
Universita' "La Sapienza"Roma, 00185 Italy
(Talk,
We-12:00)
A contextual experimental demonstration of the UOQCM and of the U-NOT gate for quantum
information is reported. The adopted apparatus, a Quantum Injected Optical Parametric Amplifier (QIOPA), realizes simultaneously
and contextually two processes which are "forbidded" by fundamental quantum limitations,
namely violate the content of two distinct axioms of structural quantum
theory, namely, the "linerarity" and the "complete positivity" of any quantum map. The subtle link
between these concepts, suggested by the present contextual experiment are discussed.
ELECTROMAGNETIC-FIELD
QUANTIZATION AND SPONTANEOUS
DECAY IN LEFT-HANDED MEDIA
Ho Trung Dung1,2,
Stefan Yoshi Buhmann1, Ludwig Knöll1, Dirk-Gunnar
Welsch1
1Theoretisch-Physikalisches
Institut, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena,
Germany
2Institute of Physics,
National Center of Sciences and Technology, 1 Mac Dinh Chi Street, District 1,
Ho Chi Minh City,Vietnam
(Talk, Tu-9:40)
Since the fabrication of
left-handed materials has been feasible, these materials have been of
increasing interest. Their unusual properties result from the fact that the
refractive index can become negative in some frequency interval. The strong dispersion
observed therein is unavoidably associated with material absorption according
to the Kramers-Kronig relations. Quantization of the electromagnetic field in
the presence of left-handed media therefore requires inclusion in the theory of
both a permittivity and a permeability that are complex functions of frequency.
The quantization scheme given here is based on introducing appropriate noise
sources into the phenomenological Maxwell equations and constructing a
Hamiltonian from which the equations of motion for the medium-assisted
electromagnetic field and the equations of motions of the charged particles
coupled to it can be derived in a consistent way. The theory is then applied to
the spontaneous decay of an excited (two-level) atom in a left-handed medium,
and the dependence of the decay rate on the atomic transition frequency is
discussed, where the local-field correction is treated within the real-cavity
model.
Miloslav Dusek
Department of Optics, Palacky University
17. listopadu 50, 772 00 Olomouc, Czech Republic
(Talk, Th-11:30)
We present the experimental realization of a programmable device
("quantum multimeter") for the error-free discrimination of two
nonorthogonal states of a qubit. The particular pair of states that shall be
unambiguously discriminated is specified by the quantum state of a single
"program" qubit. Both the "data" and "program"
qubits are represented by polarization states of photons.
Valeri Dvoeglazov
Universidad de Zacatecas, Zacatecas, Zac.
(Talk, Mo-18:40)
Recently, the problems have been found in
the definition of the partial derivative in the case of presence of
explicit and implicit functional dependencies in the classical analysis. In
thisTalk we investigate the influence of this observation on the quantum
mechanics and classical/quantum
field theory. Surprisingly, some commutators of the coordinate-dependent
operators are not equal to zero. Therefore, we try to provide
mathematical foundations to the modern non-commutative theories.
Pedro Basilio Espinoza
Padilla
Universidad de Guadalajara, Marcelino
García Barragán No.1421, Col. Olímpica,
C. P. 44420 Guadalajara,
Jal.
(Poster, Tu-17:30)
The evolution of first and second moments for non-linear spin
Hamiltonians in the semiclassical limit is analized. The exact quantum
evolution is compared with quasiclassical and parametrical approximations. In
particular, it is shown that spin squeezing can be described as the
semiclassical evolution of a given quantum state.
CASIMIR FORCES IN NONLOCAL MEDIA
R. Esquivel,
C. Villarreal, L. Mochan
Instituto de Fisica, UNAM. Apdo. postal 20-364,
Mexico 01000 D.F.
(Talk, Th-17:40)
We present
preliminary results on the effects that spatial dispersion has on Casimir
forces between realistic materials. In particular, using a simple hidrodynamic model
we calculate the nonlocal dielectric response of a semi-infinite media and a
thin layer over a substrate. The resulting Casimir force is calculated between
two parallel slabs. The effects of nonlocal effects is discussed in comparison
with recent experimental work, as well as with the results obtained from local
models.
POLYNOMIAL DEFORMATIONS OF THE
HEISENBERG-WEYL ALGEBRA
David J. Fernández C.,1 Juan Manuel Carballo,2 Javier
Negro2, and Luis
M. Nieto3
1Departamento de Física,
CINVESTAV, AP 14-740, 07000, México DF
2ESFM and ESIA, Instituto
Politécnico, Nacional U.P. Adolfo López Mateos,
07738 México D.F.
3Departamento de Física
Teórica, Universidad de Valladolid, 47011 Valladolid, Spain
(Talk, We-11:50)
Deformations of the Heisenberg-Weyl algebra, in which the commutator of
the generalized annihilation and creation operators is a polynomial of order m
in the Hamiltonian, are studied.
Natural realizations are provided by the higher order supersymmetric
partners of the harmonic oscillator (for even values of m), and of the
radial oscillator (for odd m-values). It is shown that the most general
systems ruled by such algebras involve the fourth and fifth Painlevé
transcendents for m=2 and m=3 respectively.
QUANTUM DERIVATION OF THE MANLEY ROWE RELATIONS
M. Fernández Guasti1 and H. Moya-Cessa2
1UAM-I, México, D.F.
2INAOE, Puebla, Pue.
(Talk, We-12:30)
The Ermakov Lewis quantum invariant for the time dependent harmonic
oscillator is economically derived and expressed in terms of number and phase operators.
The identification of these variables is made in accordance with the
correspondence principle and the amplitude and phase representation of the
classical orthogonal functions invariant. The relationship between the number
and phase operators is established through this invariant as the system evolves
from one frequency to another. In the specific case where the excitations
represent the photon number, these relations are equivalent to the power
density transport equations derived in nonlinear optical processes.
Periodic minimum-uncertainty states
GW Forbes1, MA Alonso2,
and AE Siegman3
1QED Technologies Inc., 1040 University Ave., Rochester NY 14607, USA
2Centro de Ciencias Físicas, Universidad Nacional
Autónoma de México
Apdo. Postal 48-3, Cuernavaca Mor. 62260, México
3Edward L. Ginzton Laboratory and Department of Electrical
Engineering
Stanford University, Stanford
CA 94305, USA
(Talk, Mo-18:00)
Among all distributions of
a given width, a minimum-uncertainty state (MUS) has a Fourier representation
of smallest possible width. (These widths are defined in terms of the
second moments of the squared modulus of the distribution.) That is, a
MUS attains the limit set by the uncertainty relation. More generally, a
MUS can be found with any desired width, centroid, and mean frequency. A
similarly general set of MUS’s is derived here for the discrete Fourier
transform, leading to discrete, periodic analogues of the
Hermite-Gaussian functions and to uncertainty relations for the DFT.
Analogous results follow for continuous periodic functions and their Fourier
series coefficients.
ENERGY FLUCTUATIONS
INDUCED BY STOCHASTIC FREQUENCY
CHANGES IN ATOM TRAPS
I. Gallardo, S. Hacyan and R. Jáuregui
Instituto de
Física, Universidad Nacional Autónoma de México,
Apdo. Postal
20-364, México D. F. 01000, México
(Poster, Tu-17:30)
We study the quantum description of energy
fluctuations induced by stochastic changes in the frequency of atom traps.
Using the connection between classical and quantum descriptions of parametric
oscillators, the classical cummulant expansion method is used to obtain quantum
results beyond standard perturbation theory with which we compare. Both the
case of static and time dependent traps are explicitly worked out.
POLARIZATION SQUEEZING AND
NON SEPARABLE BEAMS WITH COLD ATOMS
Elisabeth
Giacobino, Alberto Bramati, Vincent Josse, Aurelien Dantan, Laurent
Vernac, Michel Pinard
CNRS, Université Paris 6, France
(Talk, Th-17:00)
We study the interaction
of a nearly resonant linearly polarized laser beam with a cloud of cold cesium
atoms in a high finesse optical cavity. We observe polarization bistability and
squeezing on both the mean field mode and the orthogonally polarized mode: this
is the so called polarization squeezing. This result is confirmed by the
measurement of the Stokes parameters of the beam. The experimental results are
in good agreement with the predictions of an X-like four-level model based on
the linear input-output quantum treatment. Finally we show that this system is
able to generate two non separable orthogonally polarized beams.
ENTANGLEMENT
PROPERTIES AND TRANSFORMATIONS OF GAUSSIAN STATES
Geza Giedke
ETH Zurich,
Switzerland
(Talk, We-11:50)
Gaussian states play a
major role in several physical systems used to perform quantum information
or communication tasks. Entanglement is
an essential resource for many of these tasks.
We give an overview of the qualitative and quantitative entanglement
properties of Gaussian states and discuss the potential and limitations of
entanglement transformations with Gaussian means.
Generation of multimode squeezed vacuum in an OPO and application to
noiseless image amplification
Sylvain Gigan, Agnès Maitre, Nicolas Treps,
and Claude Fabre
Laboratoire Kastler-Brossel, France
(Talk, Th-17:30)
We recently showed experimentally that an OPO near confocality produces
multimode non-classical beams. Theory predicts that sub-threshold OPO near
confocality is a good candidate for the production of multimode squeezed
vacuum. In our experiment, we show an experimental realization of such states,
characterized by the striking property of "local squeezing". We
study the application of such a device to the noiseless amplification of a
multimode injected beam.
ENTANGLEMENT ASSISTED CAPACITY OF THE
BROADBAND LOSSY CHANNEL
Vittorio Giovannetti, Seth Lloyd, Lorenzo Maccone, and Peter W. Shor
Massachusetts Institute of Technology
Research Laboratory of Electronics, 50 Vassar Street Bldg. 36-497
Cambridge, MA 02139, USA.
(Talk, Mo-17:00)
We calculate the entanglement assisted capacity of a multimode bosonic
channel with loss. As long as the efficiency of the channel is above 50%, the
superdense coding effect can be used to transmit more bits than those that can
be stored in the message sent down the channel. Bounds for the other capacities
of the multimode channel are also provided.
QUANTUM LIMITS TO DYNAMICAL EVOLUTION
Vittorio Giovannetti, Seth Lloyd and Lorenzo Maccone
Massachusetts Institute of Technology
Research Laboratory of Electronics, 50 Vassar Street Bldg. 36-497
Cambridge, MA 02139, USA.
(Talk, We-12:30)
We establish the minimum time it takes for an initial state of mean
energy E and energy spread DE to
move from its initial configuration by a predetermined amount. Distances in
Hilbert space are estimated by the fidelity between the initial and final
state. In this context, we study the role of entanglement among subsystems in
speeding up the dynamics of a composite system.
Roy J. Glauber
Lyman Laboratory of Physics, Harvard University
Cambridge, Massachusetts 02138, USA
Sudhakar Prasad
Center for Advanced Studies and Department of Physics and Astronomy
University of New Mexico, Albuquerque, New Mexico 87131, USA
(Talk, Th-10:40)
A weakly excited medium of
resonant atoms radiates coherently by means of an infinite succession of
exponentially decaying polarization modes. A few of these modes may be
superradiant, may be but most others decay much more slowly than the
spontaneous decay of isolated atoms. They thus represent coherently trapped
excitations. Interference of the amplitudes radiated by different modes leads
to radiated power that exhibits a highly non-trivial time-dependent ringing as
well as a complex frequency spectrum consisting of sharp peaks and dips. We
present an analytical study of the problem for a spherical medium.
S. Hacyan and R. Jáuregui
Instituto de Física,
Universidad Nacional Autónoma de México, México, D.F.
(Poster, Tu-17:30)
We study the fully relativistic properties of Bessel beams with angular
momentum, using the formalism of Hertz potentials. We show that the
electromagnetic field takes a simpler form in an inertial frame moving with a
certain speed, rather than in the laboratory frame. Using this fact, we study
the motion of charged particles in the combined field of a Bessel beam and a
magnetic field. It is shown that the whole structure has the properties of a
wave guide. Some possible applications are discussed.
MORSE’S DISPLACEMENT
STATES
M. A. Hernández y
Hernández
and R. Jáuregui
Instituto de Física,
Universidad Nacional Autónoma de México,
Apdo. Postal
20-364, México D. F. 01000, México
(Poster,
Tu-17:30)
A Morse’s displacement
states results from applying the displacement operator to the ground state of the
Morse system. It is one of the multiple alternatives to extend the concept of
coherent states to nonlinear Hamiltonians. In this work we describe the quantum
evolution of these states in phase space under Morse Hamiltonian. The
parameters are chosen to describe the nonlinear vibrations of realistic molecules.
John Howell
Dept. of Physics and Astronomy
University of Rochester, Rochester NY 14627
(Talk, Th-12:00)
Much theoretical effort has been exerted to beat the universal quantum
cloning fidelity limit. One successful approach proposed by Dagmar Bruss
et al has been to limit the cloning to a subset of the possible polarization
states, such as the linear polarization states. This cloning has been labelled
phase covariant cloning. In thisTalk, results from our experimental
realization will be presented.
Quantum measurement and estimation
Zdenek Hradil,
Department of Optics, 17. listopadu 50, 772 00 Olomouc, Czech
Republic
(Talk, Tu-17:00)
Quantum estimation will be presented as a versatile tool for inferring
parameters of quantum signals. Concept of maximum likelihood
estimation and associated Fisher information may be adopted for description
of information gained in the process of measurement. New achievements and
applications in quantification of entanglement and simultaneous
reconstruction of states and processes will be reported. Developed theory will
be used for reconstruction of photon number-distribution of incoming signal
using realistic detectors. The scheme with fiber-loop detector may
statistically distinguish among several photons. Similar concepts will be
applied to quantum states with continuous variables.
QUANTUM
COMPARISON
Igor Jex
FNSPE, Czech Technical
University Prague, Brehova 7, 115 19 Praha 1
(Talk, Mo-12:30)
Can we establish whether
or not two quantum systems have been prepared in the same state? We investigate
the possibilities of universal unambiguous state comparison. We show that it is
impossible to identify two or more pure unknown pure states as being identical
and construct optimal measurements for identifying them as being different. In
the case the states are known we derive the form of optimal startegies for
state comparison. In addition we report about a related problem namely the
comparison of unitary transforms. We present several strategies that accomplish
this task and discuss their efficiency.
Relation
between losses and quasiprobability distributions in CQED
R.
Juárez-Amaro and H. Moya-Cessa
Instituto
Nacional de Astrofísica, Optica y Electrónica Puebla, Pue.
(Poster, Tu-17:30)
We show that the set of
s-parametrized quasiprobability distribution functions corresponding to an
electromagnetic field in a cavity subject to dissipation can be directly
measured by means of a simple scheme.
Dynamics of entanglement between a system and its environment
Myung Shik Kim
School of Mathematics and Physics, Queen's University, Belfast BT7 1NN,
United Kingdom
(Talk, Tu-12:00)
The process of
decoherence is one of the most complex phenomena in quantum mechanics. The
process of a single-mode or single qubit system has been at the focus of study.
When a two-mode entangled system decoheres in an environment, the system loses
entanglement. We show a mechanism which disentangles the system in a
thermal environment as we highlight the role of system-environment entanglement
in this process. The thermal environment is not entangled with the system mode
interacting with it but the other system mode which never interacts with the
environment. For this study, we show how the system evolution is
decomposed into simple linear operators.
SQUEEZE-LIKE LANGUAGE SPOKEN
BY OPTICAL INSTRUMENTS
Y.S.Kim
Department of Physics, University of Maryland, College Park, Maryland 20742,
U.S.A.
(Talk, We-12:50)
In ray optics, the basic scientific language consists of two-by-two matrices. The Jones matrix in
polarization is two-by-two, the S-matrix for multilayer optics is
two-by-two, the lens and translation
matrices in lens optics are two-by-two, the laser cavity matrices are also
two-by-two. There are many other two-by-two matrices in optics.
These small matrices are mathematically simple enough, but also form a
representation of the six-parameter Lorentz group. Those parameters are
needed for the generators of the Lie algebra, consisting of three rotation
generators and three squeeze generators. On the other hand, only one
squeeze and two rotation matrices are needed to start constructing the most
general form of the two-by-two matrices needed in optics, as well as in the
Lorentz group. The S-matrix in multilayer
optics is used to illustrate this point.
It is shown that multilayer optics can serve as an analogue computer for Wigner's little groups, group
contractions, and group
expansions. Conversely, the Lorentz group is the basic language for most, if not all, of the
optical instruments used in laboratories.
How
far apart are classical and quantum systems?
J. Klauder
Florida State University,
USA
(Talk, Fr-9:40)
As is well known, classical systems approximate quantum ones but
how well? We introduce a definition of a "distance" on classical and
quantum phase spaces that offers a measure of their separation. Such a distance
scale provides a means to measure the quality of approximate solutions to
various problems. A simple application is discussed.
Rotating wave approximation and resonance
expansion in quantum optics
Andrei Klimov
Universidad de Guadalajara, Guadalajara, Jal.
(Talk, Mo-17:00)
We propose a general approach to treat in a perturbative manner quantum optical models without the Rotating Wave
Approximation. We show that a generic Hamiltonian describing interaction
between two subsystems can be represented as a series on operators describing
transitions between energy levels of the whole system, such that these
transitions become resonant under ceratin relations between frequencies of
interacting subsystems. Then, the application of the Rotating Wave
Approximation leads to a separation of an appropriate transition, meanwhile all
the other transitions can be considered as a small perturbation. All possible
resonances are classified and approximate integrals of motion corresponding to
each resonance are found. Examples of field-field, field-atom and atom-atom
interactions are considered.
A local simulation of
EPR-Bcorrelations
A. F. Kracklauer
PF 2040; 99425 Weimar,
Germany
(Talk, Mo-18:20)
Based on a classical
calculation of EPR-B correlations as described in J. Opt. B Q&S, 4, S121
(2002), we describe a simulation protocol that mimics the generation of
individual photoelectrons. As the physics underlying this simulation is
only Malus' Principle, it is fully "local" and
"realistic;" nevertheless, the statistics violate Bell
inequalities. We describe preliminary results of simulations of the usual
models of EPR experiments as well as unrealizable counterfactual experiments.
Interaction
and fusion of Dirac fields
Peter Kramer
Institut fuer Theoretische
Physik der Universitaet
Auf der Morgenstelle
14,72076 Tuebingen, Germany
(Talk, We-13:10)
We start from the
fundamental notion due to Newton and Wigner (1949) of an elementary system and
generalize it to a Lie group manifold G as configuration space and the
irreducible representations of G as states. For G the Poincaré group we explore
massive fields and relativistic position operators. Pairs of Dirac fields
form elementary systems on the direct product manifold GxG, interactions are
taken with symmetry group (GxG). The concept of fusion due to L. de Broglie
(1932-34) is analyzed on GxG. For Dirac fields it yields the symmetric vector
fields of Bargmann and Wigner (1948) of spin S=1, and antisymmetric
scalar counterparts. Triple Dirac fields form bases for subfermion dynamics,
Stumpf (2001).
Theoretical
tools for describing matter waves from quantum sources
Tobias Kramer
Physik-Department, T30c
Technische Universitaet Muenchen
James-Franck-Str. 85748
Garching Germany
(Talk, Mo-18:40)
We utilize the
energy-dependent Green function and the concept of quantum sources to analyze
scattering of matter waves into long-range electromagnetic or gravitational
force fields. As one application we consider a realistic three-dimensional,
analytically solvable atom-laser model in the presence of gravity: An ideal Bose-Einstein condensate acts as a
stationary source that continuously releases atoms by radio-wave induced spin
flips. The calculated total emission rate and the density profile of the beam
are in good agreement with existing experimental data. Furthermore, the
excitation pattern, interference between atom beams from weakly coupled
condensates, and the engineering of wave functions are discussed.
Fiber-optic quantum communication
Prem Kumar
Northwestern University, USA
(Talk, Tu -11:30)
Abstract: One main challenge facing the widespread deployment of
quantum information technology is
the difficulty associated with transmission of quantum information through lossy and noisy channels. This
problem can be mitigated if, for
example, one could freely deploy entanglement generating devices throughout the quantum communication
network. Omnipresence of quantum
entanglement as a resource over short distances would then make possible the
implementation of entanglement purifying and entanglement swapping protocols for long-distance quantum
communication. With the ubiquitous
standard optical fiber serving as the transmission medium, technological synergy between the generation
and propagation components of the
overall quantum network can be achieved by deploying sources of entanglement that rely on the nonlinearity
of the fiber itself. In order to
develop such sources, we have been conducting experiments with
fiber-optic devices that can be used as
building blocks for fiber-based sources of
entanglement. In recent experiments we have demonstrated the generation
of entangled photons by means of the
Kerr nonlinearity of optical fiber.
Bell inequalities are violated by almost ten standard deviations of noise in
the measurements. Progress towards distributing entanglement over long fiber
lines will be presented at the conference.
Controlled Entanglement of Complex
Systems
G.Kurizki
The Weizmann Institute of
Science , Rehovot 76100 , Israel
(Talk, Tu-9:00)
It is shown that currently available techniques allow us to controllably
entangle complex quantum systems with many degrees of freedom. Thereby, the
simultaneous processing of large amounts of quantum information may
become possible, and the quantum - classical boundary may be pushed
towards macroscales. Molecular dissociation, collisions and long-range
interactions are prime examples of rich and robust sources of entanglement in
complex systems.
RELATIVE STATE OPERATOR APPROACH TO
ENTANGLEMENT MATCHING
Z. Kurucz1 , M. Koniorczyk1,2, P. Adam1,2,
and J. Janszky1,2
1Department of Nonlinear and Quantum
Optics, Research Institute for Solid
State Physics and Optics, Hungarian Academy of Sciences, PO Box 49 H-1525
Budapest, Hungary
2Research Group for Nonlinear Optics, Hungarian
Academy of Sciences, and Institute of Physics, University of Pécs, Ifjúságút 6. H-7624 Pécs, Hungary
(Talk, Th-12:00)
A relative state operator
formalism is introduced to
describe bipartite pure entanglement.
We show that the description of
quantum communication schemes like
teleportation or
entanglement swapping using nonmaximally entangled resources becomes much simpler. We present a
condition called ``entanglement matching:'' the
shared resource and the state
onto which the measurement projects
must have similar structure in
order to obtain
faithful conditional teleportation.
GRAVITATIONAL DECOHERENCE OF ATOMIC INTERFEROMETERS
B Lamine1, M.T. Jaekel2 and S.
Reynaud1
1 Laboratoire
Kastler Brossel, Campus Jussieu case 74, F-75252 Paris, France
2 Laboratoire de Physique
Théorique, Ecole Normale Supérieure, 24 rue Lhomond, F-75231 Paris, France
(Talk,
Mo-12:00)
We study the decoherence process associated with the scattering of stochastic gravitational waves. For macroscopic systems such as the planetary motion of the moon, this decoherence mechanism largely dominates the one associated with scattering of electromagnetic fluctuations associated with solar radiation or cosmic microwave background, though it has negligible influence on damping. For microscopic systems such as HYPER, a spatial project of atomic interferometer aiming at the detection of the Lense-Thirring effect, gravitational decoherence is shown to be negligible. These differents behaviours support the idea that the Planck mass defines a natural borderline between microscopic and macroscopic masses.
GENERATION
OF PHOTON NUMBER STATES ON DEMAND
W.
Lange and H. Walther
Max-Planck-Institut für Quantenoptik and Sektion
Physik der Universität München
D-85748 Garching, Germany - email:
wfl@mpq.mpg.de
(Talk, Fr-12:20)
Recently,
there has been increasing interest in the generation of fields containing a
preset number of photons. Single photons, for example, are required for secure
quantum communication and quantum computing. In systems with strong atom-photon
coupling, photon number states can be applied to generate multiple atom
entanglement. We investigate these phenomena in two different spectral regions.
The micromaser operates with Rydberg atoms in a microwave cavity. Due to its Q-factor of 4x1010, the
largest ever achieved in this type of experiment, photon fields can be built up
consecutively. In an equivalent experiment, we successfully combined an optical
cavity with an ion trap, allowing for the controlled generation of single
photon pulses in the optical domain.
continuous variable regime
J. Laurat, T. Coudreau, N. Treps, A. Maitre and C. Fabre
Laboratoire Kastler Brossel, Paris, France
(Talk, Mo-17:20)
We report the first experimental demonstration of conditional
preparation of a non-classical state of light in the continuous variable
regime. Starting from an OPO which generates above threshold quantum intensity
correlated "twin beams", we keep the recorded values of the signal
intensity only when the idler intensity
falls inside a band of values narrower than its standard deviation. By this
very simple technique, we generate a sub-Poissonian state 4.4dB (64%) below
shot noise from twin beams exhibiting 7.5 dB (82%) of noise reduction in the
intensity difference.
Optical fiber solitons and Stokes
variables for quantum communication
Gerd Leuchs
University of Erlangen-Nuernberg
Staudtstr. 7/B2 D-91058 Erlangen,
(Talk,
Tu-15:00)
GermanyIntense light pulses may exhibit quantum properties such as entanglement. Experiments are reported in which the quantum properties of intense 1,5 micrometer optical pulses are ontrolled via their non-linear interaction with the optical fiber material. The quantum properties are enhanced when operating the pulses in the Soliton regime. The conjugate quantum variables used to describe the quantum solitons are amplitude and phase quadratures or conjugate Stokes parameters. The latter approach has the advantage that direct detection is sufficient but it is more involved because the commutator of the Stokes operators is an operator itself. The experimental progress towards the implementation of quantum communication protocols is discussed.
Antonín Lukš and Vlasta Perinová
Palacky University, Czech Republic
(Talk, Mo-17:40)
We have generalized the analysis of a recent experiment [J. Audretsch et
al., T. Konrad, and A. Scherer,
2002, Phys. Rev. A 65, 033814] to more than one photon in cavities.
Enhancing the uncertainty in the phase of one mode, the measurement
influences the dynamics of coupled cavities. A quantum nondemolition
method to measure the number of photons
has been considered [M. Brune et al., S. Haroche, J. M. Raimond, L. Davidovich,
and N. Zagury, 1992, 1992, Phys. Rev. A 45, 5193]. We have shown that a
feedback mechanism still well counteracts the disturbance of the original
switching of light caused by the measurement. Connections with continuous
quantum nondemolition measurements of photon number are investigated.
Experiments
with a nonlocal single photon
Alexander
Lvovsky
Fachbereich Physik, M696,
Universität Konstanz, D-78464 Konstanz, Germany
(Talk, Tu-10:20)
The two-mode quantum state
|0,1> - |1,0> of a single photon entangled with vacuum is generated by
when a single photon is incident upon a symmetric beam splitter. We present a
series of experiments demonstrating nonlocal properties of this state and its
potential for quantum technology applications, such as quantum teleportation
and remote quantum state preparation. The initial single-photon pulses are
generated by means of conditional measurements on biphotons produced in
spontaneous parametric down-conversion and homodyne tomography is used for
quantum state characterization.
Quantum feedback and the quantumness of
macroscopic systems.
Stefano Mancini
Dipartimento di Fisica, Universita' di Camerino
I-62032 Camerino, Italy
(Talk,Mo--15:30)
Feedback provides a useful tool
to drive a system into a desired
state. Can it be profitably used to
take a macroscopic system into a state
revealing purely quantum features? The aim of theTalk is to answer this
question by employing the quantum
theory of feedback. It requires to couple the (macroscopic) system to a readout
meter (radiation field) and to an
actuator (coherent driving field). Then, it is first considered a scheme for
producing spin squeezing on a
macroscopic sample of atoms. Further on, it is shown the possibility to
cool a macroscopic mechanical oscillator, like a pendular mirror, down to the
quantum limit, displaying squeezing and
entanglement.
Margarita A. Man'ko
P.N. Lebedev Physical Institute, Leninsky Prospect 53
119991 Moscow, Russian Federation
(Talk, Th-17:00)
Linear
and nonlinear signals described by Schroedinger equations (both linear and nonlinear ones) are mapped onto
standard probablity distribution functions (tomograms). Integral transf orms
providing the wavelet and quasidistribution description of the signals
are connected with the tomographic
integral transform in explicit form. Soliton solutions of nonlinear
dynamical equations including the Schroedinger equation with cubic nonlinearity
are studied in the tomographic representation.
Bright and dark solitons of matter waves related to Bose-Einstein condensate and their tomograms are considered.
Entanglement and entropy properties related to the tomographic probability
distributions characterizing the linear and nonlinear signals are studied
Olga V. Man'ko
P.N. Lebedev Physical Institute, Leninsky Prospect 53
119991 Moscow, Russian Federation
(Talk, Th-17:40)
The photon number tomography
scheme is generalized to the case of multimode light. The reconstruction
formula for density operator of the multimode state is obtained in explicit
form. Relation to star-product formalism is established. Connection with entanglement properties of the light modes and light
state tomograms is elucidated.
Vladimir Man'ko
P.N. Lebedev Physical Institute, Leninsky Prospect 53
119991 Moscow, Russian Federation
(Talk, Mo-11:30)
The tomography map is used
to introduce the description of
quantum states by the standard probability distribution function instead of wave function and
density matrix. Star-product
quantization is related to the procedure suggested. Evolution equation and
stationary-state equation of quantum
system are presented in the form of
classical-like equations of Fokker-Planck type. Quantum transitions are
described by standard transition
probabilities instead of complex transition probability amplitudes.
Explicit invertible relations between
the transition probabilities and
complex transition probability amplitudes are obtained. Example of quantum
kinetic equations describing the decoherence processes in the new probability representation of quantum states
is considered.
Jesus Martínez Linares
Universidad de Michoacán
(Talk, Mo-18:20)
We introduce a measure Q of the ”quality” of a quantum which-way
detector, which characterizes its intrinsic ability to extract which-way
information in an asymmetric two-way interferometer. The “quality” Q allows one
to separate the contribution to the distinguishability of the ways arising from
the quantum properties of the detector from the contribution stemming from a
priori which-way knowledge available to the experimenter, which can be
quantified by a predictability parameter P. We provide an inequality relating
these two sources of which-way information to the value of the fringe visibility
displayed by the interferometer. We show that this inequality is an expression
of duality, allowing one to trace the loss of coherence to the two reservoirs
of which-way information represented by Q and P.
CONTROLLING SUPERCONDUCTING FLUX QUBITS VIA
QUANTIZED ELECTROMAGNETIC FIELDS
INFM, Dipartimento di
Scienze Fisiche ed Astronomiche dell’Università di Palermo
Via Archirafi 36, 90123
Palermo, Italy.
A. Konstadopoulou, A. Vourdas
Department of Computing, University of Bradford, Bradford BD7 1DP, United Kingdom.
T.P. Spiller
Hewlett-Packard Laboratories, Filton Road, Stoke, Gifford, Bristol BS34
8QZ, United Kingdom.
(Talk, Fr-10:40)
We present recent results highlighting the role of a quantized
electromagnetic field of a resonant tank circuit as tool of control of the
dynamics of a superconducting flux qubit. We find that the entanglement within
the qubit-field system may be controlled acting upon appropriate external
parameters. The possibility of generating maximally entangled quantum
superpositions of the two macroscopically distinguishable clockwise and
counterclockwise supercurrents states is demonstrated. We also show that a system consisting of two
Josephson qubits coupled through a quantum monochromatic electromagnetic field
mode can be used as an entangling gate, operating with decent fidelity to a
square-root of swap gate and could form the basis for initial experimental investigations
of coupled superconducting qubits.
Quantum
information experiments with entangled photons
M. W. Mitchell, C. W. Ellenor, J. S.
Lundeen and A. M. Steinberg
Physics Department, University of Toronto, Toronto, ON , M4X 1A7 CANADA
(Talk, Th-12:30)
We describe experiments
with entangled states of light for application to quantum information
processing. It is well known that a simple beamsplitter can prepare or select
entangled polarization states in a probabilistic manner. This effect has
been used for Bell inequality measurements and for quantum teleportation.
We use quantum process tomography (QPT) to fully characterize this effect under
realistic experimental conditions. This is the first application of quantum process tomography to a wo-photon operation. Experiments to
characterize and avoid decoherence will also be discussed.
A consistent quantum model for continuous photodetection processes
S. S. Mizrahi
Departamento de Física, CCET, Universidade Federal de Sao Carlos, Via
Washington Luiz km 235, 13565-905, Sao Carlos, SP, Brazil
(Talk, Th-15:30)
The photocount theory is
reviewed in the scope of the measurement process in quantum mechanics. We
discuss the continuous photodetection
model, as proposed by Srinivas and Davies [Optica Acta, 1981, vol. 28, 981], which describes the
non-unitary evolution of a quantum field state subjected to a continuous
photocount measurement, and also
present its inherent inconsistencies. We show how these inconsistencies are overcomed by introducing few but important modifications: we
redefine the `annihilation' and `creation' operators that enter in the
photocount superoperators. This new approach not only still satisfies all the requirements for a consistent photocount
theory, according to Srinivas and Davies precepts, but also avoids some weird
results.
QUANTUM INTERFERENCE AND QUANTUM
MOTION
Giovanna
Morigi
Universitaet Ulm, Germany
(Talk, Fr-10:10)
In thisTalk I discuss
quantum interference in driven
multilevel atoms, and its dependence on the atomic motion in the light field. The dynamics of the atomic center-of-mass motion and of
the electromagnetic field are
investigated, and possibilities of
controlling the phase of the quantum states are discussed.
Two aspects
of the time-energy uncertainty relation
M. Moshinski
Instituto de
Física, UNAM, A.P. 20-364, 01000 México, D.F.
(Talk,
Th-11:30)
Among the uncertainty
relations in quantum mechanics the one between time and energy is the most
difficult to communicate. In this communication we will try to show clearly two
aspects of this relation, the first one connected to the uncertainty when an
impenetrable shutter is opened for a given amount of time, and the second
related to the amount of time a compound particle lives.
Optimal
reconstruction of a pure qubit state with local measurements
Ramón Muñoz Tapia
Dept of Physics and IFAE, University
Autonoma of Barcelona 08193 Bellaterra (Barcelona), Spain
(Talk,
We-10:10)
Quantum state estimation
is a central issue in quantum information processing. Optimal strategies
for reconstructing the unknown state of
a pure qubit when onme has access to several identical copies of the state
require generalized collective measurements. These are in general very
difficult to implement physically. I
will report on the optimal strategies when only local von Neumann
measurement are used. The asymptotic limit will be shown to saturate the
collective measurement bound.
TWO-PHOTON ATOMIC MICROSCOPY USING
PATH ENTANGLEMENT
A.
Muthukrishnan,
M. O. Scully and M. S. Zubairy
Institute for Quantum Studies and Department of Physics, Texas A&M
University, College Station, Texas 77843
(Talk, Mo-17:00)
Path entanglement refers
to correlations in photon number between two distinct paths. Higher order
correlations of the field provide fringe resolution beyond the classical
Rayleigh limit. This is analogous to the
Hanbury-Brown-Twiss effect applied to photon number states. We study two-photon
path entanglement as a tool for sub-wavelength microscopy on a fixed array of
atoms. Even when each atom emits only one photon, we find that an
effective path entanglement arises in the field that is sensitive to the
locations and ordering of the emitters. This provides us with a new
spatial characterization of the degree of path entanglement.
LOSS INDUCED LONG-LIVED ENTANGLEMENT IN A
MULTIATOM SAMPLE
A. Napoli S. Nicolosi, A. Messina
INFM, MIUR and Dipartimento di Scienze Fisiche ed Astronomiche
via Archirafi 36, 90123 Palermo, Italy
(Talk, Mo-17:20)
Over the last few years it has been theoretically demonstrated the the
coupling of a two-level atoms pair to
an electromagnetic environment can be exploited to drive the atomic system into
entangled pure states immune from quantum coherence losses. To produce and
to be able to modify at will the level
of entanglement stored in a mesoscopic array of qubits, is an undoubtedly
desirable target in the framework of Quantum Computation. We present a new
proposal for generating long-lived entangled states of a material sample of N
two-level atoms giving also their explicit form.
Cecilia Noguez, C.E. Roman-Velazquez, C.
Villarreal and R. Esquivel-Sirvent
Instituto de Física,
Universidad Nacional Autónoma de México
Apartado Postal 20-364,
México DF 01000
(Talk, Th-18:00)
We develop a spectral representation formalism to calculate the Casimir
force, in the non-retarded limit, or van der Waals force between a spherical
particle and a substrate, both with arbitrary local dielectric properties. The
spectral formalism allows to study the system as a function of its geometrical
properties separately from its dielectric properties. The calculated force is
attractive, and at a small separations it is orders of magnitude larger for
nanometric-size spheres than for micrometer particles. We also found that the
force depends more on the dielectric properties of the sphere than of the
substrate. We show that the highly inhomegenous electromagnetic field induced
by the presence of the substrate, can enhance the Casimir force by orders of
magnitude, compared with the dipolar approximation.
Statistical
properties of pump and probe fields in
EIT
and related coherent effects in atomic vapor
Paulo A. Nussenzveig
Instituto de Física,USP, Sao Paulo, SP
BRAZIL
(Talk, Tu-16:00)
Recent measurements
of statistical properties of pump and probe fields interacting with atoms in a
room-temperature vapor, in a situation of Electromagnetically Induced
Transparency, will be presented. Both
fields develop super-poissonian intensity fluctuations and become correlated by
their interaction with the atoms. A
theoretical model, in which the fields are treated quantum-mechanically, was
developed and presents good qualitative agreement with the experimental
results. The experiments were conducted
with diode lasers, which have large excess phase-noise. An extension to a case
in which the fields are initially in coherent states will be discussed,
suggesting the possibility of observing entanglement between macroscopic
fields.
Conditional dynamics in cavity QED; what we
have learned about squeezing and quantum feedback.
Luis A. Orozco
Department of Physics and Astronomy, SUNY Stony Brook,
Stony Brook NY 11794-3800, United States
(Talk, Th-9:00)
Correlation measurements in a cavity QED system show the
connection between squeezing and the time evolution of the conditional
electromagnetic field. These
measurements permit to quantify squeezing in a way that is
independent of the quantum efficiency of the detectors.
The correlation measurements prepare conditional states that
show the dynamics of cavity QED. Quantum feedback
permits the modification of the dynamics with the capture and release of
the conditional state. I will review our recent work in cavity QED in the areas
of squeezing and quantum feedback.
Work done in collaboration with H. J. Carmichael, H. M.
Wiseman, P. R. Rice, G. T. Foster, J. E. Reiner,
W. P. Smith, and M. L. Terraciano with support from NSF and NIST.
PERFECT TRANSMISSION OF A FIELD ANTIBUNCHING VIA CONTINUOUS-VARIABLE
TELEPORTATION
Miguel Orszag,
Pontificia Universidad
Católica, Santiago, Chile
(Talk, Fr-11:30)
We optimize the transmission of the quantum features in light fields,
such as squeezing and antibunching,
using continous variable teleportation and
tuning the variable gain in Bob´s output.
Correlation Effects in Weakly Coupled
Bose-Einstein Condensates
Carlos Leopoldo Pando
Lambruschini
BUAP,
Puebla, Pue.
(Talk, Th-17:20)
We consider the discrete nonlinear Schroedinger equation in a ring
geometry with on-site defects as a model for a Bose-Einstein condensate (BEC)
gas confined in a deep optical lattice. For zero defects, the stationary
solutions become quasi-periodic oscillations with small perturbations. However, depending on the defects,
synchronous quasi-periodic oscillations or
synchronous chaotic energy equipartition between the condensates are observed. Both effects are robust
Quantum computers in phase space
J.P. Paz
Universidad de Buenos Aires, Argentina
(Talk, Th-10:10)
Systems with a finite dimensional Hilbert space can be represented in phase space by using discrete Wigner
functions. In thisTalk we will review this formalism and use it to represent
the states and the evolution of a quantum computer (a system of N qubits
evolving under a unitary operator that represents a quantum algorithm). We will
also describe efficient tomographic techniques to measure the discrete Wigner
function at any phase space point (or at given phase space regions). The
extension of these tomographic techniques to measure other phase space
distribution functions (Husimi, Kirkwood) will also be discussed.
Carlos Francisco Pineda
Universidad Nacional
Autonoma de Mexico, Instituto de
Fisica. Apdo. Postal 20-364,
México, D.F.
(Talk, Th-18:20)
The
dynamics of a nuclear-spin quantum computer are studied. We analyze, both
analytically and numerically, the dynamical amplitude errors of a protocol
acting on pure state due to non-resonant
transitions of the system. This is done with the aid of quantum
perturbation theory and a random phase approximation. Our results show that amplitude errors saturate with the number of
qubits and grow linearly with the number of steps in the protocol and that
quantum interference plays a main roll in diminishing error.
Experimental
work towards linear optics quantum computing
Todd B.
Pittman
The Johns Hopkins
University
Applied Physics Laboratory,
Laurel, MD 20723, USA
(Talk, Mo-16:00)
We will review recent
experimental work on some of the basic building blocks of a linear optics
approach to quantum computing, including a quantum memory device for
single-photon qubits, and a post-selected controlled-NOT logic gate.
These experiments rely on nonclassical multi-photon interference effects
obtained by mixing pulsed parametric down-conversion sources and weak coherent
states. In addition to quantum information applications, these experiments
have allowed the demonstration of phenomena of a more fundamental nature, such
as a violation of Bell's inequalities with photons from independent sources.
Quantum Phase Locking, Cyclotomy and Ramanujan Sums
Michel Planat1 and
Haret Rosu2
1Laboratoire de Physique et Métrologie des
Oscillateurs du CNRS, France
2Potosinian Institute of Scientific and
Technological Research, San Luis Potosi, SLP
(Talk, Th-18:00)
Phase-locking
governs the phase noise in classical clocks. We seek here for a quantum
counterpart of these effects. We use a version of the Pegg-Barnett operator
defined on the set of phase-locked states. Cyclotomic symmetries in matrix
elements are revealed and related to the Ramanujan sums of prime number theory,
which are sums over the primitive characters of the group of integers modulo
the dimension of the finite Hilbert space. The phase-number commutator vanishes
as in the classical case, but a new type of quantum phase noise emerges in
expectation values of phase and phase variance. The theory emphasizes the
isomorphism between algebraic number theory and quantum theory of entanglement
with strong relationships to recent work on quantum computation and the hidden
subgroup problem.
A NOVEL QUANTUM CRYPTOGRAPHIC PROTOCOL BASED ON BRIGTH TWIN BEAMS
POLARIZATION AND INTENSITY CORRELATIONS
A. Porzio, M.G.A. Paris, V. D'Auria, A. Chiummo and S. Solimeno
INFM – Coherentia, Unità di Napoli
Complesso Universitario di
Monte Sant’Angelo, via Cintia, 80126 Napoli, Italy
(Talk, Mo-17:40)
We present a novel quantum cryptographic protocol that exploits
continous wave twin beam generated by a type-II OPO. Quantum intensity and
polarization correlations of the beams are employed to guarantee protocol
security against an individual Eve attack Authentication is achieved by a
ternary randomization of beam polarization. The scheme is analysed in terms of
achieveable Bit Error Rate.
Revisiting Maths-Type q-Deformed Coherent States
Christiane Quesne
Physique Nucleaire Theorique et Physique Mathematique,
Universite Libre de Bruxelles,
Campus de la Plaine CP229, Boulevard du Triomphe, B-1050
Brussels, Belgium
(Talk, We-11 :30)
Up to now maths-type q-deformed coherent states have been restricted to
the parameter range 0 < q < 1. Here we show that for q >1, they are
normalizable on the whole complex plane and allow a resolution of unity in the
form of an ordinary integral with a simple positive-definite weight function.
They have some nonclassical properties relevant to quantum optics, such as
antibunching, quadrature squeezing, and enhancement of the signal-to quantum
noise ratio. They may also have interesting applications in the context of a
harmonic oscillator with both minimal length and momentum uncertainties, as
suggested by some considerations in string theory and quantum gravity.
NON LINEAR EFFECTS IN THE
OPTICAL RESPONSE OF AN ANHARMONIC SYSTEM
José Fco.
Recamier Angelini
Centro de
Ciencias Físicas, UNAM
Apdo. Postal
48-3 Cuernavaca, Mor.,
(Poster, Tu-17:30)
We consider a
semi-infinite system made up of a continuous distribution of entities harmonic
and anharmonic), each of which responds nonlinearly to the gradient of the
field. We start by considering a Hamiltonian consisting of a harmonic
oscillator in the presence of a spatially varying electromagnetic field E(r,t).
The interaction term m. E(r,t) is expanded around the
equilibrium position and terms up to second order are kept. The algebraic
structure of the total Hamiltonian is closed under commutation and the exact
solution for the time evolution operator can be obtained, then we compare the
second order effects evolving with 2w with the results obtained by Mendoza and
Mochan1 using perturbation theory. Next, following Man'ko2
we consider a deformed oscillator where the deformation function is chosen such
that the energy spectrum of the system is similar to that of a Morse potential.
In this case, when the non linear terms are included in the Hamiltonian its
algebraic structure does not close under commutation and we have to make
several approximations in order to obtain the time evolution operator. For the
linear case, the solution can be obtained exactly and we get an analytic expression for the linear polarizability
which shows a correction term that is a function of the ratio between the
excitation of the system and the number of bound states supported by the
potential. We compare the second order effects in the harmonic and anharmonic
cases as a function of the potential's depth.
1 Bernardo
Mendoza and W. Luis Mochán, Phys. Rev. B {\bf 53}, 4999 (1996).
2 V. I. Man'ko, G. Marmo,
F. Zaccaria, E. C. G. Sudarshan, Proceedings of the IV Wigner Symposium, Eds.
Natig Atakishiyev, Thomas Seligman and Kurt Bernardo Wolf, (World Scientific
1996).
FUNCTION OF A MIRROR
Blas M. Rodríguez and H. Moya-Cessa
INAOE, Puebla, Pue.
(Poster, Tu-17:30)
We
analyze the possibility of measuring the state of a movable mirror by using its
interaction with a quantumfield. We show that measuring the field quadratures
allows us to reconstruct the characteristic function corresponding to the
mirror state.
decay channels
José Luis Romero Ibarra
Universidad de Guadalajara, Marcelino García Barragán No.1421, Col.
Olímpica,
C. P. 44420 Guadalajara,
Jal.
(Poster, Tu-17:30)
We obtain an operational
solution for decaying systems which allows coherent population transfer among
several channels. The cases of dependent and independent decaying channels
are considered. Examples of a
collection of non-identical two level atoms, three level atoms with arbitrary
orientation of atomic transition dipoles, etc. are given.
QUANTUM CONTROL OF TWO-LEVEL SYSTEMS
Oscar Rosas-Ortiz
Departamento de Fisica,
CINVESTAV
A.P. 14-740, 07000 Mexico
DF, MEXICO
(Talk, We-12:50)
The dynamical processes for
which any spin-1/2 state evolves cyclically is analized. The
involved magnetic fields are explicitly derived by means of
inverse techniques.
Cyclotomic Quantum Clock
Haret C. Rosu (IPICyT, Mexico), Michel Planat (LPMO,
France)
(Talk, Th-17:20)
We introduce a cyclotomic quantum clock based on the Pegg-Barnett [1] quantum
phase formalism with a coprimarity (cyclotomic) constraint. This is a promising
procedure in which quantum and number theory discrete features are bunched together leading to interesting consequences
[2].
[1] DT Pegg, SM Barnett, PRA 39 (1989) 1665.
[2] A Peres, Am. J. Phys. 48 (1980) 552.
Degree of
entanglement of two atoms coupled to a cavity field
J.A. Roversi and
A. Vidiella-Barranco
Instituto de
Física "Gleb Wataghin", Universidade Estadual de Campinas,
13083-970
Campinas SP Brazil
H. Moya-Cessa
INAOE,
Coordinación de Optica, Apdo. Postal 51 y 216, 72000 Puebla, Pue.
(Poster, Tu-17:30)
We investigate the
dynamics of entanglement in a tripartite system, which consists of two
two-level atoms interacting with a single mode cavity field, but not in direct
interaction with each other. We consider one atom resonant with the cavity
field while the other is very far from resonance (dispersive limit). We
investigate the degree of entanglement of the atoms with the field using
different criteria for entanglement and we also discuss possible implications
to quantum information. Different initial preparations of the field are
considered.
Dynamics
of resonant atom interacting with a quantum cavity field in the presence of
many off-resonant atoms
Isabel Sainz Abascal.
Universidad de Guadalajara,
Marcelino García Barragán No.1421, Col. Olímpica,
C. P. 44420 Guadalajara,
Jal.
(Poster, Tu-17:30)
The dynamics of resonant atom interacting with a quantum cavity field in
the presence of many off-resonant atoms is studied. In frame of the
effective Hamiltonian approach we show
that the results of elimination of non-resonant transitions are (a) the
dynamical Stark shift of the field frequency dependent of the populations of
non-resonant atoms, (b) the dependence of the coupling constant between the
resonant atom and the field on the populations of non-resonant atoms, (c) the
effective dipole-dipole interaction between non-resonant atoms. Two effects
(the coherent influence and dephasing) of the off-resonant environment on the
resonant atom dynamics are discussed.
1Departamento de Optica,
Facultad de Fisica, Universidad
Complutense, 28040 Madrid, Spain
2 Department of Microelectronics and Information
Technology, Royal Institute of Technology (KTH), Electrum 229, SE-164 40 Kista,
Sweden
(Talk, We-13:00)
It has been recently claimed that ``the use of entangled photons in an imaging system can exhibit effects that cannot be mimicked by any other
two-photon source, whatever strength of the correlations between the two
photons'' [A. F. Abouraddy, B. E. A. Saleh, A. V. Sergienko, and M. C. Teich,
Phys. Rev. Lett. 87, 123602 (2001)].
While we believe that the cited statement is true, we show that the method
proposed in that paper, with ``bucket detection'' of one of the photons, will
give identical results for entangled states as for appropriately prepared
classically.
1Departamento de Optica,
Facultad de Fisica, Universidad
Complutense, 28040 Madrid, Spain
2 Departamento de Fisica,
Universidad de Guadalajara, Revolucion 1500, 44410 Guadalajara, Jalisco, Mexico
3 University of Lakehead, 955 Oliver Road, Thunder Bay, Ontario,Canada
(Talk, Mo-18:00)
We discuss the inequivalent configurations of a three-level quantum
system. We identify also their quite different behaviours when they interact with
quantum and classical fields. We explore the role played by the phase in an
accurate description of the qutrit as well as in the characterization of the
entanglement of qutrits. The general POVM describing an acceptable phase is
deduced.
Trapped Ion
Quantum Information Processing at NIST (*)
T. Schatz
National Institute of Standards and
Technology, 325 Broadway,Boulder, CO 80305, USA
(Talk, Th-17:50)
We will review
experimental progress towards the development of a quantum computer based on
trapped atomic ions. We will discuss
the implementation of single qubit operations and a strategy for a large scale
device will be described. Recent
results concerning the implementation of a universal two qubit phase gate and
sympathetic cooling will also be presented.
(*) Supported by NSA/ARDA
and NIST
DISTILLING GAUSSIAN STATES
Stefan Scheel
QOLS, Blackett Laboratory, Imperial College London,
Prince Consort Road, London SW7 2BW, United Kingdom
(Talk, We-11:30)
Recently it has been shown that distilling Gaussian states with Gaussian
operations only is impossible [1]. Therefore, in order to distill one has to
enlarge the class of quantum operations. I will discuss an astonishingly simple
iterative procedure that is based on distinguishing the presence or absence of
photons to achieve this task [2]. Furthermore, I will present some results on
Procrustean methods of entanglement concentration based on measurement-induced
nonlinearities.
[1] J.Eisert,
S.Scheel, and M.B.Plenio, Phys. Rev. Lett. 89, 137903 (2002).
[2] D.E.Browne,
J.Eisert, S.Scheel, and M.B.Plenio, Phys. Rev. A, accepted.
KERNEL REPRESENTATIONS OF THE WIGNER FUNCTION:AN OPERATIONAL APPROACH"
Wolfgang P. SchleichAbteilung für Quantenphysik, Universität Ulm, D-89069 Ulm, Germany(Talk, We-9:00)
We present operational definitions of the Wigner function[1]. One method relies on the Fresnel transform of measured Rabi oscillations and allows us to measure the quantum state of a harmonic oscillator such as the field in a cavity or the motional state of an ion stored in a trap. We also introduce a discrete version of this representaion. Moreover, we generalize this technique to atomic wave packets and include a representition based on a kernel transformation of the autocorrelation function. In particular, we show that for an energy spectrum that is proportional to an integer power of the quantum number the Wigner function is the autocorrelation function at half of the revival time. Me make contact to experiments in ion trap physics and cavity QED. [1] P. Lougovski, E. Solano, Z. M. Zhang, H. Walther, H. Mack, and W. P. Schleich, "Fresnel Representations of the Wigner Function: An Operational Approach", Phys. Rev. Lett. (accepted).
Entanglement and versus autocorelation
functions
Thomas Seligman
CIC, Cuernavaca, Mor.
(Talk, Th-12:30)
Auto-correlation functions are often believed to contain most of the
information about purity of a state. We shall give a rigurous inequality and
show, that cross-correlation functions must be used to get a complete picture.
The results will be applied to study the evolution of random and coherent
states under echo dynamics.
Alessio Serafini
Dipartimento di Fisica "E.R. Caianiello", Università di
Salerno,
Via S. Allende, 84081, Baronissi (SA) Italy
(Talk, We-13:10)
As well known, decoherence plays a crucial role in quantum information.
We will show how it is possible to monitor the exact evolution of
purity (or of its conjugate quantity,
known as "mixedness", characterizing decoherence) for Gaussian
states of single-mode continuous variable systems, both in thermal
and squeezed thermal baths. We derive initial and asymptotic
conditions which, at any given time, maximize purity. These proved
to be initial coherent states evolving in thermal baths or initial squeezed
states evolving in `orthogonally
squeezed' baths. The extension of this method to other
relevant states (Schroedinger cats, multimode states...) is discussed.
Swarnamala Sirsi
(Talk, Mo-18:20)
A new scheme of constructing any pure and mixed spin states using
spinors pointing along different axes in space is discussed. It is a natural generalization of
Schwinger's idea of realizing a spin-s pure state |sm> as made up of (s+m)
`up' spinors and (s-m) `down' spinors, all defined with respect to a single
axis in space. The notion of classical
correlation and quantum correlation (entanglement) is analyzed using our
model. Relationship between spin
squeezing, entanglement and spin-spin correlations is brought out explicitly by
considering some simple examples.
Allan
Solomon & Sonia Schirmer
The
Open University, UK
(Talk, We-11:30)
Nature, in the form of dissipation,
inevitably intervenes in our efforts to control a quantum system. Such
effects are not always
counterproductive; for example, the transformation from a thermal
(mixed) state to a cold condensed (pure state) can only be achieved by
non-unitary effects such as those present in dissipation. However,
although the dissipative effects are
not under our control, they are nevertheless constrained. In thisTalk we describe the resulting relationships between the various
dissipation parameters (population relaxation and phase decoherence terms) and
give a description of the process both geometrically - as motion in a
generalized Bloch ball -and algebraically - in terms of appropriate semi-groups.
Approaching
the Heisenberg limit with two mode squeezed states
Ole Steuernagel
Department of Physical Sciences, University of Hertfordshire,
Hatfield AL10
United Kingdom
(Talk, Fr-12:40)
Two mode squeezed
states can be used to achieve Heisenberg limit scaling in interferometry: a
phase shift of Df ~ 2.76 / < N > can be
resolved. The proposed scheme relies on balanced homodyne detection and can be
implemented with current technology. The most important experimental
imperfections are studied and their impact quantified.
Deposition
Rates and Noise Properties of Quantum Lithography Schemes
Ole
Steuernagel
Department of Physical Sciences, University of Hertfordshire,
Hatfield AL10
United Kingdom
(Poster, Tu-17:30)
It is shown that some assumptions about the concentration behavior
of free photons in an entangled multi-photon quantum state, published in recent
literature, were too optimistic. This greatly affects the performance of
quantum lithography schemes. Here the corresponding illumination and absorption
rates are estimated and shown to be very low. Consequently the deposition rates
are very low. With increasing photon number N the schemes become increasingly
inefficient. The noise properties of quantum lithography schemes are also
analyzed; the noise is large and affects their feasibility as well.
Detecting
N-particle interference patterns with linear balanced
N-port analyzers
Ole Steuernagel
Department of Physical Sciences, University of Hertfordshire,
Hatfield AL10
United Kingdom
(Poster, Tu-17:30)
A standard two-path
interferometer fed into a linear N-port analyzer with coincidence detection of
its output ports is analyzed. The N-port is assumed to be implemented as a
discrete Fourier transformation, i.e., to be balanced. For unbound bosons it
allows us to detect N-particle interference patterns with an N-fold reduction
of the observed de Broglie wavelength, perfect visibility and minimal noise.
Because the scheme involves heavy filtering a lot of the signal is lost, yet,
it is surprisingly robust against common experimental imperfections, and can be
implemented with current technology.
NOISE-THRESHOLD-FREE QUANTUM CRYPTOGRAPHYDenis Sych, Boris Grishanin, Victor Zadkov, and Anatoly ChirkinInternational Laser Center and Faculty of Physics,M. V. Lomonosov Moscow State University, 119899 Moscow, Russia(Poster, Tu-17:30)
A new quantum cryptography protocol employing transmission
of unselected information between input and output of a quantum channel, is
proposed. It is shown that its information properties can be substantially
better than of all other known protocols. For the objective comparison of
different crypto-protocols a new criterion, which universally reflects their
information characteristics, is proposed.
STEADY STATE ENTANGLEMENT OF TWO ATOMS
Ryszard Tanas1 and Zbigniew Fizek2
1Nonlinear Optics Division, Institute of
Physics, Adam Mickiewicz University, Pozna, Poland\newline
2Department of Physics, School of Physical
Sciences, The University of Queensland, Brisbane,
QLD 4072, Australia
(Talk, Fr-13:00)
The steady-state entanglement can be created in a system of two
two-level atoms which are separated by an arbitrary distance r12 and interact with each other
via the dipole-dipole interaction and both are driven by a laser field. The
maximally entangled antisymmetric state of the two-atom system plays an
important role in producing entanglement, and it is included in our
calculations. The steady-state value of the entanglement depends strongly on
the population of this state. We discuss conditions for getting considerable
amounts of entanglement in a system with two identical or nonidentical atoms.
Different mechanisms leading to effective transfer of population to the
antisymmetric state are identified, and different measures of entanglement are
used to compare the the values of entanglement that can be obtained in the
system.
Scheme for continuous variable teleportation
on a macroscopic body
Paolo Tombesi
Department of Physics, University of Camerino
I-62032 Camerino, Italy
(Talk, Mo-12:00)
Teleportation of an unknown quantum state is its immaterial transport through a classical
channel, followed by its
reconstruction, using the quantum resource of entanglement. Recently, it has been shown the possibility to
entangle two movable mirrors by simply
using radiation pressure effects. The
possibility of generating such an entanglement at macroscopic level suggests an avenue for achieving teleportation
of an unknown quantum state on a
macroscopic oscillator. It will be
shown how this could be achieved and the limitations imposed by the environment
will be discussed.
Engineering
correlated photons for quantum information
processing
applications
A. B.
U'Ren, E. Mukamel, C. Sliwa, K. Banaszek, and I. A. Walmsley
Oxford University, UK
(Talk, Mo-15:00)
We analyse means to
control spatio-temporal characteristics of photons generated in the process of
spontaneous parametric down-conversion. Such control is necessary to achieve
high-visibility interference in
multiple-pair experiments without deleterious effects of filtering. It also
offers a possibility to generate continous-variable entanglement in the
spectral and the spatial degrees of freedom. In this context, we present our
recent experiment to determine the transverse spatial coherence in the Wigner
representation. We also present a scheme for conditional preparation of maximal
polarisation entanglement based on partial detection of a three-pair term from
the spontaneous down-conversion output.
Phase
formalism using Turski operator
J.M.
Vargas Martínez and H. Moya-Cessa
INAOE,
Puebla, Pue.
(Poster, Tu-17:30)
We present a phase
formalism that passes the Pegg-Barnett acid test, i.e. the variance for a number state is given by p2 /3. The formalism is shown to have
consistency subjected to different
approaches.
ASPECTS OF THE
INTERACTION OF TRAPPED IONS WITH THE QUANTIZED FIELD
Antonio Vidiella-Barranco
UNICAMP, Campinas, SP, Brazil
(Talk, Mo-17:20)
Trapped ions manipulated by electromagnetic fields have
allowed the generation of a variety of quantum states as well as quantum logic
operations. Another important system is constituted by flying atoms interacting
with the quantized cavity field. In the past years there have been efforts to
merge those two worlds, i.e., to consider a single trapped ion inside a high
quality cavity. In this Talk I am going to discuss the generation of
nonclassical states, quantum effects, logic operations assisted by the
quantized cavity field, as well as the influence of the cavity losses upon the
processes above mentioned.
Polarization
qubit phase gate in driven atomic media
David Vitali
Università
di Camerino, Italy
(Talk, Th-16:00)
We present here an
all--optical scheme for the
experimental realization of a quantum phase gate. It is based on the polarization degree of freedom
of two traveling single photon
wave-packets and exploits giant Kerr nonlinearities that can be attained in
coherently driven ultracold atomic
media.
Criteria
for the Nonclassicality of Quantum States
Werner Vogel
Arbeitsgruppe Quantenoptik,
Fachbereich Physik, Universitaet Rostock, Universitaetsplatz 3
D-18051 Rostock, Germany
(Talk, Th-15:00)
The characterization of
the nonclassicality of quantum states of
the harmonic oscillator is considered from an observational viewpoint.
Based on measurable characteristic functions we formulate necessary and
sufficient conditions for the failure of the Glauber-Sudarshan P-function to be
a probability density. The criteria are applied to several examples of quantum
states. Particular emphasis is paid on
the phase-sensitivity of the conditions, that is even relevant for the
characterization of phase-insensitive
quantum states. Extensions of the criteria to multimode quantum states are considered.
A.Vourdas
Department of Computing, University of Bradford,
Bradford BD7 1DP, United Kingdom
(Talk, We-10:40)
Composite systems comprised of N quantum systems with d-dimensional
Hilbert spaces, are considered. Local [SU(d)]N
transformations and more general SU(dN) entangling
transformations are studied. Symplectic Sp(2N, Z (d))
transformations are also studied and
the necessary matrices which perform such transformations are calculated
numerically. A simple repetition code based on the d-dimensional Hilbert
space HA spanned by the direct products of `position states'
|X;m,...m> can protect qudits from a very limited class of errors. It is
shown that a code based on the symplectically transformed space SHA can protect qudits from a
large class of errors. Numerical examples
are discussed in detail.
Quantum
noise in stochastic cooling of trapped atoms
Sascha Wallentowitz
Fachbereich Physik,
Universitaet Rostock,
Universitaetsplatz 3,
D-18051 Rostock, Germany
(Talk, Mo-12:30)
Quantum noise in
stochastic cooling of trapped atoms and its influence on the cooling limit is
studied. Being a feedback process, stochastic cooling consists of series of
measurements and subsequent conditional operations. Besides fundamental
measurement-induced quantum noise, a further source of heating can be
identified as the fluctuations of the number of atoms subject to the
feedback. At condensation temperatures they become dramatically large and
thus seem to pose a limit to stochastic cooling. Nevertheless, it is
shown that by an adjustment of control fields this limit can be circumvented,
so that cooling persists also below condensation temperatures.
Howard Mark Wiseman
School of Science, Nathan Campus, Griffith University
Brisbane QLD 4111, AUSTRALIA
(Talk, Th-9:40)
A which-way measurement destroys a twin-slit
interference pattern. Can this always be attributed to a random momentum
transfer p of order h/s (with s the slit separation and h Planck's
constant), as Bohr thought? Scully, Englert and Walther (SEW) said
"no", but others have disagreed. This work proposes a
resolution using a weak-valued momentum transfer probability distribution P(p).
I show that P(p) must be nonzero for some p: |p| > h/6s. Nevertheless,
its moments can be identically zero, such as in the experiment proposed by SEW.
P(p) is experimentally measurable, and I discuss a current effort to do
just that.
Kurt Bernardo Wolf, Natig M. Atakishiyev,
George S. Pogosyan, and Luis Edgar Vicent
UNAM, Cuernavaca, Mor.
(Talk, We-12:10)
The finite oscillator model, whose position and momentum spaces are
discrete and finite, provides finite bases and transforms for discrete and finite 1-dim signals, or 2-dim
images on screens pixellated by a square or polar array of sensors. The
finite oscillator has a lowest-energy
state (the binomial distribution), a
highest-energy state, and follows the dynamics of the 'continuous' oscillator with the Lie algebra so(3)=su(2).
The finite oscillator eigenfunctions of
energy involve the Kravchuk orthogonal polynomials. The dynamical algebra
of the two-dimensional finite oscillator is so(4); reduced to so(3) + so(3) it
describes square screens, while the canonical reduction so(4) > so(3) > so(2) serves for polar
screens with 'equal-density' pixellation. In the latter case, the radial
wavefunctions are the so(3) symmetric Clebsch-Gordan coefficients, which involve the Hahn orthogonal polynomials. In every case we have a proper
discrete version of the fractional Fourier transform, and a coherent phase space
interpretation.
QUANTUM OPTICS AND QUANTUM INFORMATION
Horace P. Yuen
Northwestern University, USA
(Talk, Mo-9:40)
The role of quantum optics in the general area of quantum information
science and technology will be discussed, especially in quantum cryptography
but also quantum teleportation and quantum computation.
The crucial sensitivity issue in quantum information, not just mere
decoherence, will be raised and elaborated.
Schroedinger-Cat-Like-States from canonical
transformations in quantum phase-space
Arturo Zúñiga Segundo
Departamento de Física,
ESFM, IPN, México, D.F.
(Poster, Tu-17:30)
Employing canonical transformations defined in the coherent-state
representation of quantum mechanics, we introduce Schroedinger-Cat-Like-States.
The squeezed displaced number states with real squeezing parameter are
contained in these states. The phase-space wave functions, time-dependent
uncertainties, probability flux vectors and densities are obtained.