81,092 research outputs found
Quantum state majorization at the output of bosonic Gaussian channels
Quantum communication theory explores the implications of quantum mechanics
to the tasks of information transmission. Many physical channels can be
formally described as quantum Gaussian operations acting on bosonic quantum
states. Depending on the input state and on the quality of the channel, the
output suffers certain amount of noise. For a long time it has been
conjectured, but never proved, that output states of Gaussian channels
corresponding to coherent input signals are the less noisy ones (in the sense
of a majorization criterion). In this work we prove this conjecture.
Specifically we show that every output state of a phase insensitive Gaussian
channel is majorized by the output state corresponding to a coherent input. The
proof is based on the optimality of coherent states for the minimization of
strictly concave output functionals. Moreover we show that coherent states are
the unique optimizers.Comment: 7 pages, 1 figure. Published versio
Coherent States of Harmonic Oscillator and Generalized Uncertainty Principle
In this paper dynamics and quantum mechanical coherent states of a simple
harmonic oscillator are considered in the framework of Generalized Uncertainty
Principle(GUP). Equations of motion for simple harmonic oscillator are derived
and some of their new implications are discussed. Then coherent states of
harmonic oscillator in the case of GUP are compared with relative situation in
ordinary quantum mechanics. It is shown that in the framework of GUP there is
no considerable difference in definition of coherent states relative to
ordinary quantum mechanics. But, considering expectation values and variances
of some operators, based on quantum gravitational arguments one concludes that
although it is possible to have complete coherency and vanishing broadening in
usual quantum mechanics, gravitational induced uncertainty destroys complete
coherency in quantum gravity and it is not possible to have a monochromatic ray
in principle.Comment: 12 pages, no figur
Coherent States and Modified de Broglie-Bohm Complex Quantum Trajectories
This paper examines the nature of classical correspondence in the case of
coherent states at the level of quantum trajectories. We first show that for a
harmonic oscillator, the coherent state complex quantum trajectories and the
complex classical trajectories are identical to each other. This congruence in
the complex plane, not restricted to high quantum numbers alone, illustrates
that the harmonic oscillator in a coherent state executes classical motion. The
quantum trajectories are those conceived in a modified de Broglie-Bohm scheme
and we note that identical classical and quantum trajectories for coherent
states are obtained only in the present approach. The study is extended to
Gazeau-Klauder and SUSY quantum mechanics-based coherent states of a particle
in an infinite potential well and that in a symmetric Poschl-Teller (PT)
potential by solving for the trajectories numerically. For the coherent state
of the infinite potential well, almost identical classical and quantum
trajectories are obtained whereas for the PT potential, though classical
trajectories are not regained, a periodic motion results as t --> \infty.Comment: More example
Generalized coherent states for solvable quantum systems with degenerate discrete spectra and their nonclassical properties
In this paper, the generalized coherent state for quantum systems with
degenerate spectra is introduced. Then, the nonclassicality features and
number-phase entropic uncertainty relation of two particular degenerate quantum
systems are studied. Finally, using the Gazeau-Klauder coherent states
approach, time evolution of some of the nonclassical properties of the coherent
states corresponding to the considered physical systems are discussed.Comment: 17 pages, 10 figures,Physica A: Statistical Mechanics and its
Applications, Article in Pres
- …