1,068 research outputs found
Entanglement criteria via the uncertainty relations in su(2) and su(1,1) algebra: detection of non-Gaussian entangled states
We derive a class of inequalities, from the uncertainty relations of the
SU(1,1) and the SU(2) algebra in conjunction with partial transposition, that
must be satisfied by any separable two-mode states. These inequalities are
presented in terms of the su(2) operators J_x, J_y, and the total photon number
N_a+N_b. They include as special cases the inequality derived by Hillery and
Zubairy [Phys. Rev. Lett. 96, 050503 (2006)], and the one by Agarwal and Biswas
[New J. Phys. 7, 211 (2005)]. In particular, optimization over the whole
inequalities leads to the criterion obtained by Agarwal and Biswas. We show
that this optimal criterion can detect entanglement for a broad class of
non-Gaussian entangled states, i.e., the su(2) minimum-uncertainty states.
Experimental schemes to test the optimal criterion are also discussed,
especially the one using linear optical devices and photodetectors.Comment: published version, presentation polished with references added, 7
pages, 4 figure
Single-shot measurement of quantum optical phase
Although the canonical phase of light, which is defined as the complement of
photon number, has been described theoretically by a variety of distinct
approaches, there have been no methods proposed for its measurement. Indeed
doubts have been expressed about whether or not it is measurable. Here we show
how it is possible, at least in principle, to perform a single-shot measurement
of canonical phase using beam splitters, mirrors, phase shifters and
photodetectors.Comment: This paper was published in PRL in 2002 but, at the time, was not
placed on the archive. It is included now to make accessing this paper easie
Cosmological Perturbations of Quantum-Mechanical Origin and Anisotropy of the Microwave Background
Cosmological perturbations generated quantum-mechanically (as a particular
case, during inflation) possess statistical properties of squeezed quantum
states. The power spectra of the perturbations are modulated and the angular
distribution of the produced temperature fluctuations of the CMBR is quite
specific. An exact formula is derived for the angular correlation function of
the temperature fluctuations caused by squeezed gravitational waves. The
predicted angular pattern can, in principle, be revealed by the COBE-type
observations.Comment: 9 pages, WUGRAV-92-17 Accepted for Publication in Phys. Rev. Letters
(1993
Phase properties of hypergeometric states and negative hypergeometric states
We show that the three quantum states (Plya states, the
generalized non-classical states related to Hahn polynomials and negative
hypergeometric states) introduced recently as intermediates states which
interpolate between the binomial states and negative binomial states are
essentially identical. By using the Hermitial-phase-operator formalism, the
phase properties of the hypergeometric states and negative hypergeometric
states are studied in detail. We find that the number of peaks of phase
probability distribution is one for the hypergeometric states and for the
negative hypergeometric states.Comment: 7 pages, 4 figure
Linear amplification and quantum cloning for non-Gaussian continuous variables
We investigate phase-insensitive linear amplification at the quantum limit
for single- and two-mode states and show that there exists a broad class of
non-Gaussian states whose nonclassicality survives even at an arbitrarily large
gain. We identify the corresponding observable nonclassical effects and find
that they include, remarkably, two-mode entanglement. The implications of our
results for quantum cloning outside the Gaussian regime are also addressed.Comment: published version with reference updat
Statistics of Raman-Active Excitations via Masurement of Stokes-Anti-Stokes Correlations
A general fundamental relation connecting the correlation of Stokes and
anti-Stokes modes to the quantum statistical behavior of vibration and pump
modes in Raman-active materials is derived. We show that under certain
conditions this relation can be used to determine the equilibrium number
variance of phonons.Time and temperature ranges for which such conditions can
be satisfied are studied and found to be available in todays' experimental
standards. Furthermore, we examine the results in the presence of multi-mode
pump as well as for the coupling of pump to the many vibration modes and
discuss their validity in these cases.Comment: 12 pages, 1 figure, accepted for publication in Phys.Rev.
Novel approach to the study of quantum effects in the early universe
We develop a theoretical frame for the study of classical and quantum
gravitational waves based on the properties of a nonlinear ordinary
differential equation for a function of the conformal time
, called the auxiliary field equation. At the classical level,
can be expressed by means of two independent solutions of the
''master equation'' to which the perturbed Einstein equations for the
gravitational waves can be reduced. At the quantum level, all the significant
physical quantities can be formulated using Bogolubov transformations and the
operator quadratic Hamiltonian corresponding to the classical version of a
damped parametrically excited oscillator where the varying mass is replaced by
the square cosmological scale factor . A quantum approach to the
generation of gravitational waves is proposed on the grounds of the previous
dependent Hamiltonian. An estimate in terms of and
of the destruction of quantum coherence due to the gravitational
evolution and an exact expression for the phase of a gravitational wave
corresponding to any value of are also obtained. We conclude by
discussing a few applications to quasi-de Sitter and standard de Sitter
scenarios.Comment: 20 pages, to appear on PRD. Already published background material has
been either settled up in a more compact form or eliminate
Roper excitation in reactions
We calculate differential cross sections and the spin transfer coefficient
in the reaction for proton
bombarding energies from 1 to 10 GeV and invariant masses spanning
the region of the N(1440) Roper resonance. Two processes --
excitation in the -particle and Roper excitation in the proton -- are
included in an effective reaction model which was shown previously to reproduce
existing inclusive spectra. The present calculations demonstrate that these two
contributions can be clearly distinguished via , even under kinematic
conditions where cross sections alone exhibit no clear peak structure due to
the excitation of the Roper.Comment: 12 pages, 11 ps figures, Late
Position-momentum local realism violation of the Hardy type
We show that it is, in principle, possible to perform local realism violating
experiments of the Hardy type in which only position and momentum measurements
are made on two particles emanating from a common source. In the optical
domain, homodyne detection of the in-phase and out-of-phase amplitude
components of an electromagnetic field is analogous to position and momentum
measurement. Hence, local realism violations of the Hardy type are possible in
optical systems employing only homodyne detection.Comment: 10 pages, no figures, to be published in Physical Review
States interpolating between number and coherent states and their interaction with atomic systems
Using the eigenvalue definition of binomial states we construct new
intermediate number-coherent states which reduce to number and coherent states
in two different limits. We reveal the connection of these intermediate states
with photon-added coherent states and investigate their non-classical
properties and quasi-probability distributions in detail. It is of interest to
note that these new states, which interpolate between coherent states and
number states, neither of which exhibit squeezing, are nevertheless squeezed
states. A scheme to produce these states is proposed. We also study the
interaction of these states with atomic systems in the framework of the
two-photon Jaynes-Cummings model, and describe the response of the atomic
system as it varies between the pure Rabi oscillation and the collapse-revival
mode and investigate field observables such as photon number distribution,
entropy and the Q-function.Comment: 26 pages, 29 EPS figures, Latex, Accepted for publication in J.Phys.
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