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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

- Read more about Data-pattern tomography of entangled states. (arXiv:1701.04891v1 [quant-ph])
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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

- Read more about Quantum enhanced measurements without entanglement. (arXiv:1701.05152v1 [quant-ph])
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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.