1,397 research outputs found
Phase space interference and the WKB approximation for squeezed number states
Squeezed number states for a single mode Hamiltonian are investigated from
two complementary points of view. Firstly the more relevant features of their
photon distribution are discussed using the WKB wave functions. In particular
the oscillations of the distribution and the parity behavior are derived and
compared with the exact results. The accuracy is verified and it is shown that
for high photon number it fails to reproduce the true distribution. This is
contrasted with the fact that for moderate squeezing the WKB approximation
gives the analytical justification to the interpretation of the oscillations as
the result of the interference of areas with definite phases in phase space. It
is shown with a computation at high squeezing using a modified prescription for
the phase space representation which is based on Wigner-Cohen distributions
that the failure of the WKB approximation does not invalidate the area overlap
picture.Comment: 9 pages, 4 figure
On the Squeezed Number States and their Phase Space Representations
We compute the photon number distribution, the Q distribution function and
the wave functions in the momentum and position representation for a single
mode squeezed number state using generating functions which allow to obtain any
matrix element in the squeezed number state representation from the matrix
elements in the squeezed coherent state representation. For highly squeezed
number states we discuss the previously unnoted oscillations which appear in
the Q function. We also note that these oscillations can be related to the
photon-number distribution oscillations and to the momentum representation of
the wave function.Comment: 16 pages, 9 figure
Dimensional enhancement of kinetic energies
Simple thermodynamics considers kinetic energy to be an extensive variable
which is proportional to the number, N, of particles. We present a quantum
state of N non-interacting particles for which the kinetic energy increases
quadratically with N. This enhancement effect is tied to the quantum
centrifugal potential whose strength is quadratic in the number of dimensions
of configuration space.Comment: 9 pages, accepted by Phys. Rev.
The Generalized Hartle-Hawking Initial State: Quantum Field Theory on Einstein Conifolds
Recent arguments have indicated that the sum over histories formulation of
quantum amplitudes for gravity should include sums over conifolds, a set of
histories with more general topology than that of manifolds. This paper
addresses the consequences of conifold histories in gravitational functional
integrals that also include scalar fields. This study will be carried out
explicitly for the generalized Hartle-Hawking initial state, that is the
Hartle-Hawking initial state generalized to a sum over conifolds. In the
perturbative limit of the semiclassical approximation to the generalized
Hartle-Hawking state, one finds that quantum field theory on Einstein conifolds
is recovered. In particular, the quantum field theory of a scalar field on de
Sitter spacetime with spatial topology is derived from the generalized
Hartle-Hawking initial state in this approximation. This derivation is carried
out for a scalar field of arbitrary mass and scalar curvature coupling.
Additionally, the generalized Hartle-Hawking boundary condition produces a
state that is not identical to but corresponds to the Bunch-Davies vacuum on
de Sitter spacetime. This result cannot be obtained from the original
Hartle-Hawking state formulated as a sum over manifolds as there is no Einstein
manifold with round boundary.Comment: Revtex 3, 31 pages, 4 epsf figure
Entangled coherent states versus entangled photon pairs for practical quantum information processing
We compare effects of decoherence and detection inefficiency on entangled
coherent states (ECSs) and entangled photon pairs (EPPs), both of which are
known to be particularly useful for quantum information processing (QIP). When
decoherence effects caused by photon losses are heavy, the ECSs outperform the
EPPs as quantum channels for teleportation both in fidelities and in success
probabilities. On the other hand, when inefficient detectors are used, the
teleportation scheme using the ECSs suffers undetected errors that result in
the degradation of fidelity, while this is not the case for the teleportation
scheme using the EPPs. Our study reveals the merits and demerits of the two
types of entangled states in realizing practical QIP under realistic
conditions.Comment: 9 pages, 6 figures, substantially revised version, to be published in
Phys. Rev.
Husimi's function and quantum interference in phase space
We discuss a phase space description of the photon number distribution of non
classical states which is based on Husimi's function and does not
rely in the WKB approximation. We illustrate this approach using the examples
of displaced number states and two photon coherent states and show it to
provide an efficient method for computing and interpreting the photon number
distribution . This result is interesting in particular for the two photon
coherent states which, for high squeezing, have the probabilities of even and
odd photon numbers oscillating independently.Comment: 15 pages, 12 figures, typos correcte
Dynamical Origin of the Lorentzian Signature of Spacetime
It is suggested that not only the curvature, but also the signature of
spacetime is subject to quantum fluctuations. A generalized D-dimensional
spacetime metric of the form is
introduced, where . The corresponding
functional integral for quantized fields then interpolates from a Euclidean
path integral in Euclidean space, at , to a Feynman path integral in
Minkowski space, at . Treating the phase as just
another quantized field, the signature of spacetime is determined dynamically
by its expectation value. The complex-valued effective potential
for the phase field, induced by massless fields at one-loop, is considered. It
is argued that is minimized and is stationary,
uniquely in D=4 dimensions, at , which suggests a dynamical origin
for the Lorentzian signature of spacetime.Comment: 6 pages, LaTe
Interference in a Spherical Phase-Space and Asymptotic-Behavior of the Rotation Matrices
We extend the interference in the phase-space algorithm of Wheeler and Schleich [W. P. Schleich and J. A. Wheeler, Nature 326, 574 (1987)] to the case of a compact, spherical topology in order to discuss the large j limits of the angular momentum marginal probability distributions. These distributions are given in terms of the standard rotation matrices. It is shown that the asymptotic distributions are given very simply by areas of overlap in the classical spherical phase-space parametrized by the components of angular momentum. The results indicate the very general validity of the interference in phase-space concept for computing semiclassical limits in quantum mechanics
- …