159 research outputs found
Nonlocal feedback in nonlinear systems
A shifted or misaligned feedback loop gives rise to a two-point nonlocality
that is the spatial analog of a temporal delay. Important consequences of this
nonlocal coupling have been found both in diffusive and in diffractive systems,
and include convective instabilities, independent tuning of phase and group
velocities, as well as amplification, chirping and even splitting of localized
perturbations. Analytical predictions about these nonlocal systems as well as
their spatio-temporal dynamics are discussed in one and two transverse
dimensions and in presence of noise.Comment: 13 pages, to be published in EPJ
Resolution in rotation measurements
The limiting resolution in optical interferometry is set by the number of
photons used, with the functional dependence determined by the state of light
that is prepared. We consider the problem of measuring the rotation of a beam
of light about an optical axis and show how the limiting resolution depends on
the total number of quanta of orbital angular momentum carried by the light
beam.Comment: 14 page
Analytic stochastic treatment of a nonlinear quantum model with negative diffusion
We apply a proposal of Yuen and Tombesi, for treating stochastic problems
with negative diffusion, to the analytically soluble problem of the single-mode
anharmonic oscillator. We find that the associated stochastic realizations
include divergent trajectories. It is possible, however, to solve the
stochastic problem exactly, but the averaging must be performed with great
care.Comment: Phys.Rev.
Signal amplification and control in optical cavities with off-axis feedback
We consider a large class of optical cavities and gain media with an off-axis
external feedback which introduces a two-point nonlocality. This nonlocality
moves the lasing threshold and opens large windows of control parameters where
weak light spots can be strongly amplified while the background radiation
remains very low. Furthermore, transverse phase and group velocities of a
signal can be independently tuned and this enables to steer it non
mechanically, to control its spatial chirping and to split it into two
counter-propagating ones.Comment: 4 pages, 4 picture
Probing the spectral density of a dissipative qubit via quantum synchronization
The interaction of a quantum system, which is not accessible by direct
measurement, with an external probe can be exploited to infer specific features
of the system itself. We introduce a probing scheme based on the emergence of
spontaneous quantum synchronization between an out-of-equilibrium qubit, in
contact with an external environment, and a probe qubit. Tuning the frequency
of the probe leads to a transition between synchronization in phase and
antiphase. The sharp transition between these two regimes is locally accessible
by monitoring the probe dynamics alone and allows one to reconstruct the shape
of the spectral density of the environment
Quantum Darwinism and non-Markovian dissipative dynamics from quantum phases of the spin-1/2 XX model
Quantum Darwinism explains the emergence of a classical description of
objects in terms of the creation of many redundant registers in an environment
containing their classical information. This amplification phenomenon, where
only classical information reaches the macroscopic observer and through which
different observers can agree on the objective existence of such object, has
been revived lately for several types of situations, successfully explaining
classicality. We explore quantum Darwinism in the setting of an environment
made of two level systems which are initially prepared in the ground state of
the XX model, which exhibits different phases; we find that the different
phases have different ability to redundantly acquire classical information
about the system, being the "ferromagnetic phase" the only one able to complete
quantum Darwinism. At the same time we relate this ability to how non-Markovian
the system dynamics is, based on the interpretation that non-Markovian dynamics
is associated to back flow of information from environment to system, thus
spoiling the information transfer needed for Darwinism. Finally, we explore
mixing of bath registers by allowing a small interaction among them, finding
that this spoils the stored information as previously found in the literature
Genuine quantum and classical correlations in multipartite systems
Generalizing the quantifiers used to classify correlations in bipartite
systems, we define genuine total, quantum, and classical correlations in
multipartite systems. The measure we give is based on the use of relative
entropy to quantify the "distance" between two density matrices. Moreover, we
show that, for pure states of three qubits, both quantum and classical
bipartite correlations obey a ladder ordering law fixed by two-body mutual
informations, or, equivalently, by one-qubit entropies.Comment: Accepted for publication in Phys. Rev. Let
Synchronization along quantum trajectories
We employ a quantum trajectory approach to characterize synchronization and
phase-locking between open quantum systems in nonequilibrium steady states. We
exemplify our proposal for the paradigmatic case of two quantum Van der Pol
oscillators interacting through dissipative coupling. We show the deep impact
of synchronization on the statistics of phase-locking indicators and other
correlation measures defined for single trajectories, spotting a link between
the presence of synchronization and the emergence of large tails in the
probability distribution for the entanglement along trajectories. Our results
shed new light on fundamental issues regarding quantum synchronization
providing new methods for its precise quantification.Comment: v2: 9 + 3 pages, 5 figures. v3: few typos corrected, close to the
published versio
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