386 research outputs found
Nonlinear cross-Kerr quasiclassical dynamics
We study the quasiclassical dynamics of the cross-Kerr effect. In this
approximation, the typical periodical revivals of the decorrelation between the
two polarization modes disappear and they remain entangled. By mapping the
dynamics onto the Poincare space, we find simple conditions for polarization
squeezing. When dissipation is taken into account, the shape of the states in
such a space is not considerably modified, but their size is reduced.Comment: 16 pages, 5 figure
Sizing up entanglement in mutually unbiased bases with Fisher information
An efficient method for assessing the quality of quantum state tomography is
developed. Special attention is paid to the tomography of multipartite systems
in terms of unbiased measurements. Although the overall reconstruction errors
of different sets of mutually unbiased bases are the same, differences appear
when particular aspects of the measured system are contemplated. This point is
illustrated by estimating the fidelities of genuinely tripartite entangled
states.Comment: 7 pages. 3 color figures. Close to the published versio
Nonlinear and Quantum Optics with Whispering Gallery Resonators
Optical Whispering Gallery Modes (WGMs) derive their name from a famous
acoustic phenomenon of guiding a wave by a curved boundary observed nearly a
century ago. This phenomenon has a rather general nature, equally applicable to
sound and all other waves. It enables resonators of unique properties
attractive both in science and engineering. Very high quality factors of
optical WGM resonators persisting in a wide wavelength range spanning from
radio frequencies to ultraviolet light, their small mode volume, and tunable
in- and out- coupling make them exceptionally efficient for nonlinear optical
applications. Nonlinear optics facilitates interaction of photons with each
other and with other physical systems, and is of prime importance in quantum
optics. In this paper we review numerous applications of WGM resonators in
nonlinear and quantum optics. We outline the current areas of interest,
summarize progress, highlight difficulties, and discuss possible future
development trends in these areas.Comment: This is a review paper with 615 references, submitted to J. Op
Unpolarized states and hidden polarization
We capitalize on a multipolar expansion of the polarisation density matrix,
in which multipoles appear as successive moments of the Stokes variables. When
all the multipoles up to a given order vanish, we can properly say that the
state is th-order unpolarized, as it lacks of polarization information to
that order. First-order unpolarized states coincide with the corresponding
classical ones, whereas unpolarized to any order tally with the quantum notion
of fully invariant states. In between these two extreme cases, there is a rich
variety of situations that are explored here. The existence of \textit{hidden}
polarisation emerges in a natural way in this context.Comment: 7 pages, 3 eps-color figures. Submitted to PRA. Comments welcome
Measuring photon anti-bunching from continuous variable sideband squeezing
We present a technique for measuring the second-order coherence function
of light using a Hanbury-Brown Twiss intensity interferometer
modified for homodyne detection. The experiment was performed entirely in the
continuous variable regime at the sideband frequency of a bright carrier field.
We used the setup to characterize for thermal and coherent
states, and investigated its immunity to optical loss. We measured
of a displaced squeezed state, and found a best anti-bunching
statistic of .Comment: 4 pages, 4 figure
Orbital angular momentum from marginals of quadrature distributions
We set forth a method to analyze the orbital angular momentum of a light
field. Instead of using the canonical formalism for the conjugate pair
angle-angular momentum, we model this latter variable by the superposition of
two independent harmonic oscillators along two orthogonal axes. By describing
each oscillator by a standard Wigner function, we derive, via a consistent
change of variables, a comprehensive picture of the orbital angular momentum.
We compare with previous approaches and show how this method works in some
relevant examples.Comment: 7 pages, 2 color figure
Quasiprobability currents on the sphere
We present analytic expressions for the s-parametrized currents on the sphere for both unitary and dissipative evolutions. We examine the spatial distribution of the flow generated by these currents for quadratic Hamiltonians. The results are applied for the study of the quantum dissipative dynamics of the time-honored Kerr and Lipkin models, exploring the appearance of the semiclassical limit in stable, unstable, and tunneling regimes
Quantum limits to center-of-mass measurements
We discuss the issue of measuring the mean position (center-of-mass) of a
group of bosonic or fermionic quantum particles, including particle number
fluctuations. We introduce a standard quantum limit for these measurements at
ultra-low temperatures, and discuss this limit in the context of both photons
and ultra-cold atoms. In the case of fermions, we present evidence that the
Pauli exclusion principle has a strongly beneficial effect, giving rise to a
1/N scaling in the position standard-deviation -- as opposed to a
scaling for bosons. The difference between the actual mean-position fluctuation
and this limit is evidence for quantum wave-packet spreading in the
center-of-mass. This macroscopic quantum effect cannot be readily observed for
non-interacting particles, due to classical pulse broadening. For this reason,
we also study the evolution of photonic and matter-wave solitons, where
classical dispersion is suppressed. In the photonic case, we show that the
intrinsic quantum diffusion of the mean position can contribute significantly
to uncertainties in soliton pulse arrival times. We also discuss ways in which
the relatively long lifetimes of attractive bosons in matter-wave solitons may
be used to demonstrate quantum interference between massive objects composed of
thousands of particles.Comment: 12 pages, 6 figures. Submitted to PRA. Revised to include more
references as well as a discussion of fermionic center-of-mas
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