6,664 research outputs found
Optimal distinction between non-orthogonal quantum states
Given a finite set of linearly independent quantum states, an observer who
examines a single quantum system may sometimes identify its state with
certainty. However, unless these quantum states are orthogonal, there is a
finite probability of failure. A complete solution is given to the problem of
optimal distinction of three states, having arbitrary prior probabilities and
arbitrary detection values. A generalization to more than three states is
outlined.Comment: 9 pages LaTeX, one PostScript figure on separate pag
The Effects of Symmetries on Quantum Fidelity Decay
We explore the effect of a system's symmetries on fidelity decay behavior.
Chaos-like exponential fidelity decay behavior occurs in non-chaotic systems
when the system possesses symmetries and the applied perturbation is not tied
to a classical parameter. Similar systems without symmetries exhibit
faster-than-exponential decay under the same type of perturbation. This
counter-intuitive result, that extra symmetries cause the system to behave in a
chaotic fashion, may have important ramifications for quantum error correction.Comment: 5 pages, 3 figures, to be published Phys. Rev. E Rapid Communicatio
Quantum Cryptography with Orthogonal States?
This is a Comment on Phys Rev Lett 75 (1995) 1239, by Goldenberg and VaidmanComment: 3 pages, LaTeX, 1 figure on separate page Final version in Phys Rev
Lett 77 (1996) 326
Quantum Fidelity Decay of Quasi-Integrable Systems
We show, via numerical simulations, that the fidelity decay behavior of
quasi-integrable systems is strongly dependent on the location of the initial
coherent state with respect to the underlying classical phase space. In
parallel to classical fidelity, the quantum fidelity generally exhibits
Gaussian decay when the perturbation affects the frequency of periodic phase
space orbits and power-law decay when the perturbation changes the shape of the
orbits. For both behaviors the decay rate also depends on initial state
location. The spectrum of the initial states in the eigenbasis of the system
reflects the different fidelity decay behaviors. In addition, states with
initial Gaussian decay exhibit a stage of exponential decay for strong
perturbations. This elicits a surprising phenomenon: a strong perturbation can
induce a higher fidelity than a weak perturbation of the same type.Comment: 11 pages, 11 figures, to be published Phys. Rev.
Information-disturbance tradeoff in quantum measurements
We present a simple information-disturbance tradeoff relation valid for any
general measurement apparatus: The disturbance between input and output states
is lower bounded by the information the apparatus provides in distinguishing
these two states.Comment: 4 Pages, 1 Figure. Published version (reference added and minor
changes performed
The most probable wave function of a single free moving particle
We develop the most probable wave functions for a single free quantum
particle given its momentum and energy by imposing its quantum probability
density to maximize Shannon information entropy. We show that there is a class
of solutions in which the quantum probability density is self-trapped with
finite-size spatial support, uniformly moving hence keeping its form unchanged.Comment: revtex, 4 page
Kochen-Specker Obstruction for Position and Momentum Using a Single Degree of Freedom
It is shown that, given a reasonable continuity assumption regarding
possessed values, it is possible to construct a Kochen-Specker obstruction for
any coordinate and its conjugate momentum, demonstrating that at most one of
these two quantities can have a noncontextual value.Comment: This version replaces v1, which contained a faulty continuity
condito
Solving the Hamilton-Jacobi equation for gravitationally interacting electromagnetic and scalar fields
The spatial gradient expansion of the generating functional was recently
developed by Parry, Salopek, and Stewart to solve the Hamiltonian constraint in
Einstein-Hamilton-Jacobi theory for gravitationally interacting dust and scalar
fields. This expansion is used here to derive an order-by-order solution of the
Hamiltonian constraint for gravitationally interacting electromagnetic and
scalar fields. A conformal transformation and functional integral are used to
derive the generating functional up to the terms fourth order in spatial
gradients. The perturbations of a flat Friedmann-Robertson-Walker cosmology
with a scalar field, up to second order in spatial gradients, are given. The
application of this formalism is demonstrated in the specific example of an
exponential potential.Comment: 14 pages, uses amsmath,amssymb, referees' suggestions implemented, to
appear in Classical and Quantum Gravit
Influence of detector motion in entanglement measurements with photons
We investigate how the polarization correlations of entangled photons
described by wave packets are modified when measured by moving detectors. For
this purpose, we analyze the Clauser-Horne-Shimony-Holt Bell inequality as a
function of the apparatus velocity. Our analysis is motivated by future
experiments with entangled photons designed to use satellites. This is a first
step towards the implementation of quantum information protocols in a global
scale
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