100 research outputs found
Energy-Sensitive and "Classical-like" Distances Between Quantum States
We introduce the concept of the ``polarized'' distance, which distinguishes
the orthogonal states with different energies. We also give new inequalities
for the known Hilbert-Schmidt distance between neighbouring states and express
this distance in terms of the quasiprobability distributions and the normally
ordered moments. Besides, we discuss the distance problem in the framework of
the recently proposed ``classical-like'' formulation of quantum mechanics,
based on the symplectic tomography scheme. The examples of the Fock, coherent,
``Schroedinger cats,'' squeezed, phase, and thermal states are considered.Comment: 23 pages, LaTex, 2 eps figures, to appear in Physica Script
SU(1,1) symmetry of multimode squeezed states
We show that a class of multimode optical transformations that employ linear
optics plus two-mode squeezing can be expressed as SU(1,1) operators. These
operations are relevant to state-of-the-art continuous variable quantum
information experiments including quantum state sharing, quantum teleportation,
and multipartite entangled states. Using this SU(1,1) description of these
transformations, we obtain a new basis for such transformations that lies in a
useful representation of this group and lies outside the often-used restriction
to Gaussian states. We analyze this basis, show its application to a class of
transformations, and discuss its extension to more general quantum optical
networks
On the squeezed states for n observables
Three basic properties (eigenstate, orbit and intelligence) of the canonical
squeezed states (SS) are extended to the case of arbitrary n observables. The
SS for n observables X_i can be constructed as eigenstates of their linear
complex combinations or as states which minimize the Robertson uncertainty
relation. When X_i close a Lie algebra L the generalized SS could also be
introduced as orbit of Aut(L^C). It is shown that for the nilpotent algebra h_N
the three generalizations are equivalent. For the simple su(1,1) the family of
eigenstates of uK_- + vK_+ (K_\pm being lowering and raising operators) is a
family of ideal K_1-K_2 SS, but it cannot be represented as an Aut(su^C(1,1))
orbit although the SU(1,1) group related coherent states (CS) with symmetry are
contained in it.
Eigenstates |z,u,v,w;k> of general combination uK_- + vK_+ + wK_3 of the
three generators K_j of SU(1,1) in the representations with Bargman index k =
1/2,1, ..., and k = 1/4,3/4 are constructed and discussed in greater detail.
These are ideal SS for K_{1,2,3}. In the case of the one mode realization of
su(1,1) the nonclassical properties (sub-Poissonian statistics, quadrature
squeezing) of the generalized even CS |z,u,v;+> are demonstrated. The states
|z,u,v,w;k=1/4,3/4> can exhibit strong both linear and quadratic squeezing.Comment: 25 pages, LaTex, 4 .pic and .ps figures. Improvements in text,
discussion on generation scheme added. To appear in Phys. Script
Analytic representations based on SU(1,1) coherent states and their applications
We consider two analytic representations of the SU(1,1) Lie group: the
representation in the unit disk based on the SU(1,1) Perelomov coherent states
and the Barut-Girardello representation based on the eigenstates of the SU(1,1)
lowering generator. We show that these representations are related through a
Laplace transform. A ``weak'' resolution of the identity in terms of the
Perelomov SU(1,1) coherent states is presented which is valid even when the
Bargmann index is smaller than one half. Various applications of these
results in the context of the two-photon realization of SU(1,1) in quantum
optics are also discussed.Comment: LaTeX, 15 pages, no figures, to appear in J. Phys. A. More
information on http://www.technion.ac.il/~brif/science.htm
Measurements of Anisotropy in the Cosmic Microwave Background Radiation at Degree Angular Scales Near the Stars Sigma Hercules and Iota Draconis
We present results from two four-frequency observations centered near the
stars Sigma Hercules and Iota Draconis during the fourth flight of the
Millimeter-wave Anisotropy eXperiment (MAX). The observations were made of 6 x
0.6-degree strips of the sky with 1.4-degree peak to peak sinusoidal chop in
all bands. The FWHM beam sizes were 0.55+/-0.05 degrees at 3.5 cm-1 and a
0.75+/-0.05 degrees at 6, 9, and 14 cm-1. Significant correlated structures
were observed at 3.5, 6 and 9 cm-1. The spectra of these signals are
inconsistent with thermal emission from known interstellar dust populations.
The extrapolated amplitudes of synchrotron and free-free emission are too small
to account for the amplitude of the observed structures. If the observed
structures are attributed to CMB anisotropy with a Gaussian autocorrelation
function and a coherence angle of 25', then the most probable values are
DT/TCMB = (3.1 +1.7-1.3) x 10^-5 for the Sigma Hercules scan, and DT/TCMB =
(3.3 +/- 1.1) x 10^-5 for the Iota Draconis scan (95% confidence upper and
lower limits). Finally a comparison of all six MAX scans is presented.Comment: 13 pages, postscript file, 2 figure
Generalized thermo vacuum state derived by the partial trace method
By virtue of the technique of integration within an ordered product (IWOP) of
operators we present a new approach for deriving generalized thermo vacuum
state which is simpler in form that the result by using the Umezawa-Takahashi
approach, in this way the thermo field dynamics can be developed. Applications
of the new state are discussed.Comment: 5 pages, no figure, revtex
Continuous photodetection model: quantum jump engineering and hints for experimental verification
We examine some aspects of the continuous photodetection model for
photocounting processes in cavities. First, we work out a microscopic model
that describes the field-detector interaction and deduce a general expression
for the Quantum Jump Superoperator (QJS), that shapes the detector's
post-action on the field upon a detection. We show that in particular cases our
model recovers the QJSs previously proposed ad hoc in the literature and point
out that by adjusting the detector parameters one can engineer QJSs. Then we
set up schemes for experimental verification of the model. By taking into
account the ubiquitous non-idealities, we show that by measuring the lower
photocounts moments and the mean waiting time one can check which QJS better
describes the photocounting phenomenon.Comment: 12 pages, 7 figures. Contribution to the conference Quantum Optics
III, Pucon - Chile, November 27-30, 200
A General Theory of Phase-Space Quasiprobability Distributions
We present a general theory of quasiprobability distributions on phase spaces
of quantum systems whose dynamical symmetry groups are (finite-dimensional) Lie
groups. The family of distributions on a phase space is postulated to satisfy
the Stratonovich-Weyl correspondence with a generalized traciality condition.
The corresponding family of the Stratonovich-Weyl kernels is constructed
explicitly. In the presented theory we use the concept of the generalized
coherent states, that brings physical insight into the mathematical formalism.Comment: REVTeX, 4 pages. More information on
http://www.technion.ac.il/~brif/science.htm
Nonlinear dynamics of semiconductor lasers with active optical feedback
An in-depth theoretical as well as experimental analysis of the nonlinear dynamics in semiconductor lasers with active optical feedback is presented. Use of a monolithically integrated multi-section device of sub-mm total length provides access to the short-cavity regime. By introducing an amplifier section as novel feature, phase and strength of the feedback can be separately tuned. In this way, the number of modes involved in the laser action can be adjusted. We predict and observe specific dynamical scenarios. Bifurcations mediate various transitions in the device output, from single-mode steady-state to self-pulsation and between different kinds of self-pulsations, reaching eventually chaotic behavior in the multi-mode limit
- …