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.

# All

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