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We develop a theory to describe dynamics of a nonstationary open quantum
system interacting with a hybrid environment, which includes high-frequency and
low-frequency noise components. One part of the system-bath interaction is
treated in a perturbative manner, whereas the other part is considered exactly.
This approach allows us to derive a set of master equations where the
relaxation rates are expressed as convolutions of the Bloch-Redfield and Marcus
formulas. Our theory enables analysis of systems that have extremely small

In this contribution, we introduce a technique to freeze the parameters which
describe the accelerated states between two users to be used in the context of
quantum cryptography and quantum teleportation. It is assumed that, the two
users share different dimension sizes of particles, where we consider a
qubit-qutrit system. This technique depends on local operations, where it is
allowed that each particle interacts locally with a noisy phase channel. We
show that, the possibility of freezing the information of quantum channel

In a recent work by Novo et al. (Sci. Rep. 5, 13304, 2015), the invariant
subspace method was applied to the study of continuous-time quantum walk
(CTQW). The method helps to reduce a graph into a simpler version that allows
more transparent analyses of the quantum walk model. In this work, we adopt the
aforementioned method to investigate the optimality of a quantum walk search of
a marked element on a complete multi-partite graph. We formulate the eigenbasis

In this paper, we study a quantum harmonic oscillator in a Mach-Zehnder-type
interferometer which interacts with an environment, including electromagnetic
oscillators. By solving the Lindblad master equation, we calculate the resulted
interference pattern of the system. Interestingly, we show that even if one
considers the decoherence effect, the system will keep some of its quantum
properties. Indeed, the thermalization process does not completely leave the

We address in this paper the notion of relative phase shift for mixed quantum
systems. We study the Pancharatnam-Sjoeqvist phase shift for metaplectic
isotopies acting on Gaussian mixed states. We complete and generalize previous
results obtained by one of us while giving rigorous proofs. This gives us the
opportunity to review and complement the theory of the Conley-Zehnder index
which plays an essential role in the determination of phase shifts.

We propose a quantum optimal control algorithm that performs a gradient
descent in a reduced basis named GRadient Optimization Using Parametrization
(GROUP). We compare this optimization algorithm to the other state-of-the-art
algorithms in quantum control namely, Gradient-Ascent Pulse Engieering (GRAPE),
Krotov's method and Nelder-Mead using Chopped Random Basis (CRAB). We find that
GROUP converges much faster than Nelder-Mead with CRAB and achieves better

We study causal waveform estimation (tracking) of time-varying signals in a
paradigmatic atomic sensor, an alkali vapor monitored by Faraday rotation
probing. We use Kalman filtering, which optimally tracks known linear Gaussian
stochastic processes, to estimate stochastic input signals that we generate by
optical pumping. Comparing the known input to the estimates, we confirm the
accuracy of the atomic statistical model and the reliability of the Kalman
filter, allowing recovery of waveform details far briefer than the sensor's

We propose a Global-Local optimization algorithm for quantum control that
combines standard local search methodologies with evolutionary algorithms. This
allows us to find faster solutions to a set of problems relating to ultracold
control of Bose-Einstein condensates.

By generalizing the Cabello-Severini-Winter (CSW) framework, we build a
bridge from this graph-theoretic approach for Kochen-Specker (KS) contextuality
to a hypergraph-theoretic approach for Spekkens' contextuality, as applied to
Kochen-Specker type scenarios. Our generalized framework describes an
experiment that requires, besides the correlations between measurements carried
out on a system prepared according to a fixed preparation procedure (as in
Bell-KS type experiments), the correlations between measurement outcomes and

We analyze the energy spectrum and eigenstates of cold atoms in a tilted
brick-wall optical lattice. When the tilt is applied, the system exhibits a
sequence of topological phase transitions reflected in an abrupt change of the
eigenstates. It is demonstrated that these topological phase transitions can be
easily detected in a laboratory experiment by observing Bloch oscillations of
cold atoms.