9,849 research outputs found
Spin state in the propagation of quantum relativistic particles along classical trajectories
We address the propagation of the spin along classical trajectories for a
1/2-spin particle obeying the Dirac equation with scalar potentials. Focusing
on classical trajectories as the exact propagation of wave-function
discontinuities we find an explicit spin-transport law for the case of the
Dirac oscillator. In the general case we examine the spin propagation along
classical trajectories emerging as an approximation of the quantum dynamics via
the mechanical analog of the optical eikonal asymptotic approach. Throughout we
establish as many parallels as possible with the equivalent situation for the
electromagnetic field.Comment: 8 pages, 5 figure
SU(2)-invariant depolarization of quantum states of light
We develop an SU(2)-invariant approach to the depolarization of quantum
systems as the effect of random unitary SU(2) transformations. From it we
derive an SU(2)-invariant Markovian master equation. This is applied to several
quantum states examining whether nonclassical states are more sensible to
depolarization than the classical ones. Furthermore, we show that this
depolarization model provides a nontrivial generalization of depolarization
channels to states of arbitrary dimension.Comment: RevTex4 file, color figures, published versio
Nonlinear Michelson interferometer for improved quantum metrology
We examine quantum detection via a Michelson interferometer embedded in a gas
with Kerr nonlinearity. This nonlinear interferometer is illuminated by pulses
of classical light. This strategy combines the robustness against practical
imperfections of classical light with the improvement provided by nonlinear
processes. Regarding ultimate quantum limits, we stress that, as a difference
with linear schemes, the nonlinearity introduces pulse duration as a new
variable into play along with the energy resources.Comment: 5 pages, 1 figure. Close to published versio
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