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We show that any multi-qudit entanglement witness leads to a non-separability
indicator for quantum optical fields, which involves intensity correlation
measurements and is useful for field states of undefined photon numbers. With
the approach we get, e.g., necessary and sufficient conditions for intensity or
rate correlations to reveal polarization entanglement and separability
conditions for experiments with mutually unbiased multiport interferometers.

We show some interesting properties of tridiagonal and pentadiagonal matrices
in the weak coupling limits. In the former case of this limit the ground state
wave function amplitudes are identical to the Taylor expansion coefficients of
the exponential function e$^{(-v/E)}$. With regards to transition rates a dip
in the pentadiagonal case which is not present in the tridiagonal case is
explained. An intimate connection between energy denominators and exponential
behavior is demonstrated.

We discuss on the external temperature dependence of quantum entanglement in
coupled harmonic oscillator system. We show that entanglement sudden death
phenomenon in temperature occurs in this system. This fact implies that the
thermal entanglement completely vanishes when external temperature is greater
than the critical temperature. The critical temperature $T_c$ is derived
explicitly.

Any kind of quantum resource useful in different information processing tasks
is vulnerable to several types of environmental noise. Here we study the
behaviour of quantum correlations such as entanglement and steering in
two-qubit systems under the application of the generalised amplitude damping
channel and propose some protocols towards preserving them under this type of
noise. First, we employ the technique of weak measurement and reversal for the
purpose of preservation of correlations. We then show how the evolution under

We consider an interferometer that contains active elements, such as a
parametric amplifier, with general two-mode Gaussian unitary channels rather
than the usually considered phase-shift channel. We concentrate on a scheme
based on the recently proposed pumped-up SU(1,1) active interferometer where
all input particles participate in the parameter estimation, and from which a
conventional SU(1,1) interferometer is a limiting case. Using the covariance
matrix formalism, we derive the quantum Fisher information of this active

We theoretically study complementarity between micro-micro and micro-macro
entanglement in a Bose-Einstein condensate with two Rydberg impurities. We
investigate quantum dynamics of micro-micro and micro-macro entanglement in the
micro-macro system. It is found that strong micro-macro entanglement between
Rydberg impurities and the BEC can be generated by the use of initial
micro-micro entanglement between two Rydberg impurities, which acts as the seed
entanglement to create micro-macro entanglement. We demonstrate a curious

We propose a novel concept of coherent states geometrising a time evolution
of quantum systems. The respective coherent state transforms reduce certain
Hamiltonians to first-order differential operators, thus the dynamics can be
explicitly expressed through a flow of variables in extensions of the phase
space. This generalises the geometric dynamics of a harmonic oscillator in the
Fock space. We describe all Hamiltonians which are geometrised by Gaussian and
Airy beams and write down explicit solutions for such systems.

Recent progress in observing and manipulating mechanical oscillators at
quantum regime provides new opportunities of studying fundamental physics, for
example to search for low energy signatures of quantum gravity. For example, it
was recently proposed that such devices can be used to test quantum gravity
effects, by detecting the change in the [x,p] commutation relation that could
result from quantum gravity corrections. We show that such a correction results

We study the optimization of any quantum process by minimizing the
`randomness' in the measurement result at the output of that quantum process.
We conceptualize and propose a measure of such randomness and inquire whether
an optimization of the quantum process based on that measure, can reach the
point where the process operates with maximum fidelity. We consider approximate
quantum cloning and teleportation processes, and find, in particular, that the
optimal approximate state-dependent quantum cloning machine obtained by

The dynamics of open quantum systems and manipulation of quantum resources
are both of fundamental interest in quantum physics. Here, we investigate the
relation between quantum Markovianity and coherence, providing an effective way
for detecting non-Markovianity based on the \textit{quantum-incoherent relative
entropy of coherence} ($\mathcal{QI}$ REC). We theoretically show the relation
between completely positive (CP) divisibility and the monotonic behavior of the

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