We discuss the data-pattern tomography for reconstruction of entangled states
of light. We show that for a moderate number of probe coherent states it is
possible to achieve high accuracy of representation not only for single-mode
states but also for two-mode entangled states. We analyze the stability of
these representations to the noise and demonstrate the conservation of the
purity and entanglement. Simulating the probe and signal measurements, we show

Quantum coherence (QC) originating from quantum superposition plays a central
role in quantum mechanics. Baumgratz et al. established resource-theoretic
framework of quantifying coherence. However, until now, all most of QC
measures, which are based on this framework, are basis-dependent. As we know,
the physical properties of the physical system should not be changed with the
different choice of coordinate systems. QC as a physical property of quantum
state, should also not be changed in different basis. Therefore, a good QC

We study scattering of a composite quasiparticle, which possesses a degree of
freedom corresponding to relative coordinate of two bound excitations, by a
delta-like impurity potential on a one-dimensional discrete lattice. Firstly,
we show that, due to specific properties of their dispersion, lattice
excitations bind to impurities with both negative and positive potentials. We
demonstrate that the finite size of the composite excitation leads to formation
of multiple excitation-impurity bound states. The number and the degree of

Superconducting circuit technologies have recently achieved quantum protocols
involving closed feedback loops. Quantum artificial intelligence and quantum
machine learning are emerging fields inside quantum technologies which may
enable quantum devices to acquire information from the outer world and improve
themselves via a learning process. Here we propose the implementation of basic
protocols in quantum reinforcement learning, with superconducting circuits
employing feedback-loop control. We introduce diverse scenarios for

In this paper we construct a new type of cavity array, in each cavity of
which multiple two-level atoms interact with two independent photon modes. This
system can be totally governed by a two-mode Dicke-lattice model, which
includes all of the counter-rotating terms and therefore works well in the
ultrastrong coupling regime achieved in recent experiments. Attributed to its
special atom-photon coupling scheme, this model supports a global conserved
excitation and a continuous $U(1)$ symmetry, rather than the discrete $Z_{2}$

Quantum-enhanced measurements exploit quantum mechanical effects for
increasing the sensitivity of measurements of certain physical parameters and
have great potential for both fundamental science and concrete applications.
Most of the research has so far focused on using highly entangled states, which
are, however, difficult to produce and to stabilize for a large number of
constituents. In the following we review alternative mechanisms, notably the
use of more general quantum correlations such as quantum discord, identical

Estimating the angular separation between two incoherently radiating
monochromatic point sources is a canonical toy problem to quantify spatial
resolution in imaging. In recent work, Tsang {\em et al.} showed, using a
Fisher Information analysis, that Rayleigh's resolution limit is just an
artifact of the conventional wisdom of intensity measurement in the image
plane. They showed that the optimal sensitivity of estimating the angle is only
a function of the total photons collected during the camera's integration time

We investigate the excitation dynamics at a first-order quantum phase
transition (QPT). More specifically, we consider the quench-induced QPT in the
quantum search algorithm, which aims at finding out a marked element in an
unstructured list. We begin by deriving the exact dynamics of the model, which
is shown to obey a Riccati differential equation. Then, we discuss the
probabilities of success by adopting either global or local adiabaticity
strategies. Moreover, we determine the disturbance of the quantum criticality

We describe a compact and reliable method to calculate the Fisher information
for the estimation of a dynamical parameter in a continuously measured linear
Gaussian quantum system. Unlike previous methods in the literature, which
involve the numerical integration of a stochastic master equation for the
corresponding density operator in a Hilbert space of infinite dimension, the
formulas here derived depends only on the evolution of first and second moments

We investigate the coupled-system dynamics of two-level quantum dots placed
on a vibrating nanomechanical resonator. The ensemble of quantum dots exhibits
superradiance features which are transferred to the mechanical degrees of
freedom representing fast quantum dynamics and enhanced phonon emission in a
nanomechanical setup, resembling of the superradiance effect.