All

The work is devoted to the theoretical and experimental study of quantum
states of light conditionally prepared by subtraction of a random number of
photons from the initial multimode thermal state. A fixed number of photons is
subtracted from a multimode quantum state, but only a subsystem of a lower
number of modes is registered, in which the number of subtracted photons turns
out to be a non-fixed random variable. It is shown that the investigation of

In practical implementation of quantum key distributions (QKD), it requires
efficient, real-time feedback control to maintain system stability when facing
disturbance from either external environment or imperfect internal components.
Usually, a "scanning-and-transmitting" program is adopted to compensate
physical parameter variations of devices, which can provide accurate
compensation but may cost plenty of time in stopping and calibrating processes,
resulting in reduced efficiency in key transmission. Here we for the first

We present a detailed study of the topological Schwinger model
[$\href{this http URL}{Phys. \; Rev.\; D \; {\bf
99},\;014503 \; (2019)}$], which describes (1+1) quantum electrodynamics of an
Abelian $U(1)$ gauge field coupled to a symmetry-protected topological matter
sector, by means of a class of $\mathbb{Z}_N$ lattice gauge theories. Employing
density-matrix renormalization group techniques that exactly implement Gauss'

We apply the scattering approach to the Casimir interaction between two
dielectric half-spaces separated by an electrolyte solution. We take the
nonlocal electromagnetic response of the intervening medium into account, which
results from the presence of movable ions in solution. In addition to the usual
transverse modes, we consider longitudinal channels and their coupling by
reflection at the surface of the local dielectric. The Casimir interaction
energy is calculated from the matrix describing a round-trip of coupled

Based on his extension of the classical argument of Einstein, Podolsky and
Rosen, Schr\"odinger observed that, in certain quantum states associated with
pairs of particles that can be far away from one another, the result of the
measurement of an observable associated with one particle is perfectly
correlated with the result of the measurement of another observable associated
with the other particle. Combining this with the assumption of locality and
some ``no hidden variables" theorems, we showed in a previous paper [11] that

The real-time dynamics of systems with up to three SQUIDs is studied by
numerically solving the time-dependent Schr\"odinger equation. The numerical
results are used to scrutinize the mapping of the flux degrees of freedom onto
two-level systems (the qubits) as well as the performance of the intermediate
SQUID as a tunable coupling element. It is shown that the two-level
representation yields a good description of the flux dynamics during quantum
annealing, and the presence of the tunable coupling element does not have

In recent decades, various multipartite entanglement measures have been
proposed by many researchers, with different characteristics. Meanwhile, Scott
studied various interesting aspects of multipartite entanglement measures and
he has defined a class of related multipartite entanglement measures in an
obvious manner. Recently, Jafarpour et al. (Int. J. Quantum Inform. 13, 1550047
2015) have calculated the entanglement quantity of two-dimensional 5-site spin

Clifford gates play a role in the optimisation of Clifford+T circuits.
Reducing the count and the depth of Clifford gates, as well as the optimal
scheduling of T gates, influence the hardware and the time costs of executing
quantum circuits. This work focuses on circuits protected by the surface
quantum error-correcting code. The result of compiling a quantum circuit for
the surface code is called a topological assembly. We use queuing theory to
model a part of the compiled assemblies, evaluate the models, and make the

Langevin and Fokker-Planck equations for the Brownian motion in steep
(extremally anharmonic) potential wells of the form $U(x)= x^m/m, m=2n, n>1$
are interpreted as reliable approximations of the reflected Brownian motion in
the interval, as the potential steepness grows indefinitely. We investigate a
familiar transformation of the involved Fokker-Planck operator to the Hermitian
(eventually self-adjoint) Schr\"{o}dinger - type one $-\Delta + {\cal{V}}$,
with the two-well (bistable) potential ${\cal{V}}(x)= {\cal{V}}_m(x)=

We introduce a method for solving the Max-Cut problem using a variational
algorithm and a continuous-variables quantum computing approach. The quantum
circuit consists of two parts: the first one embeds a graph into a circuit
using the Takagi decomposition and the second is a variational circuit which
solves the Max-Cut problem. We analyze how the presence of different types of
non-Gaussian gates influences the optimization process by performing numerical

Pages