895 research outputs found
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
Open Quantum Systems. An Introduction
We revise fundamental concepts in the dynamics of open quantum systems in the
light of modern developments in the field. Our aim is to present a unified
approach to the quantum evolution of open systems that incorporates the
concepts and methods traditionally employed by different communities. We
present in some detail the mathematical structure and the general properties of
the dynamical maps underlying open system dynamics. We also discuss the
microscopic derivation of dynamical equations, including both Markovian and
non-Markovian evolutions.Comment: 100 pages, 3 figures. Updated version with typos corrected. Preprint
version of the published boo
Nonlinear fiber gyroscope for quantum metrology
We examine the performance of a nonlinear fiber gyroscope for improved signal
detection beating the quantum limits of its linear counterparts. The
performance is examined when the nonlinear gyroscope is illuminated by
practical field states, such as coherent and quadrature squeezed states. This
is compared with the case of more ideal probes such as photon-number states.Comment: 8 pages, 1 figur
Topological Heat Transport and Symmetry-Protected Boson Currents
The study of non-equilibrium properties in topological systems is of
practical and fundamental importance. Here, we analyze the stationary
properties of a two-dimensional bosonic Hofstadter lattice coupled to two
thermal baths in the quantum open-system formalism. Novel phenomena appear like
chiral edge heat currents that are the out-of-equilibrium counterparts of the
zero-temperature edge currents. They support a new concept of dissipative
symmetry-protection, where a set of discrete symmetries protects topological
heat currents, differing from the symmetry-protection devised in closed systems
and zero-temperature. Remarkably, one of these currents flows opposite to the
decreasing external temperature gradient. As the starting point, we consider
the case of a single external reservoir already showing prominent results like
thermal erasure effects and topological thermal currents. Our results are
experimentally accessible with platforms like photonics systems and optical
lattices.Comment: RevTeX4 file, color figure
On measures of non-Markovianity: divisibility vs. backflow of information
We analyze two recently proposed measures of non-Markovianity: one based on
the concept of divisibility of the dynamical map and the other one based on
distinguishability of quantum states. We provide a toy model to show that these
two measures need not agree. In addition, we discuss possible generalizations
and intricate relations between these measures.Comment: 7 pages; new section is adde
Quantum Thermodynamics in the Refined Weak Coupling Limit
We present a thermodynamic framework for the refined weak coupling limit. In
this limit the interaction between system and environment is weak, but not
negligible. As a result, the system dynamics becomes non-Markovian breaking
divisibility conditions. Nevertheless, we propose a derivation of the first and
second law just in terms of the reduced system dynamics. To this end, we extend
the refined weak coupling limit for allowing slowly-varying external drivings,
and reconsider the definition of internal energy due to the non-negligible
interaction.Comment: Color figures, invited pape
- …