The Second Law of Thermodynamics states that temporal evolution of an
isolated system occurs with non-diminishing entropy. In quantum realm, this
holds for energy-isolated systems the evolution of which is described by the
so-called unital quantum channel. The entropy of a system evolving in a
non-unital quantum channel can, in principle, decrease. We formulate a general
criterion of unitality for the evolution of a quantum system, enabling a simple
and rigorous approach for finding and identifying the processes accompanied by

A recent experiment [J. L. Garrett, D. A. T. Somers, and J. N. Munday, Phys.
Rev. Lett {\bf 120}, 040401 (2018)] measured for the first time the gradient of
the Casimir force between two gold spheres in vacuum at room temperature, and
placed a bound on the magnitude of the deviation of the measured force from the
proximity force approximation (PFA). The present work extends a previous
theoretical analysis of this experiment [G. Bimonte, Phys. Rev. D {\bf 97},

Typically, quantum mechanics is thought of as a linear theory with unitary
evolution governed by the Schr\"odinger equation. While this is technically
true and useful for a physicist, with regards to computation it is an
unfortunately narrow point of view. Just as a classical computer can simulate
highly nonlinear functions of classical states, so too can the more general
quantum computer simulate nonlinear evolutions of quantum states. We detail one
particular simulation of nonlinearity on a quantum computer, showing how the

Microresonator-based nonlinear processes are fundamental to applications
including microcomb generation, parametric frequency conversion, and harmonics
generation. While nonlinear processes involving either second- ($\chi^{(2)}$)
or third- $\chi^{(3)}$) order nonlinearity have been extensively studied, the
interaction between these two basic nonlinear processes has seldom been
reported. In this letter, we demonstrate a coherent interplay between second-

We unravel the dynamical stability of a fully polarized one-dimensional
ultracold few-fermion spin-1/2 gas subjected to inhomogeneous driving of the
itinerant spins. Despite the unstable character of the total spin-polarization
the existence of an interaction regime is demonstrated where the
spin-correlations lead to almost maximally aligned spins throughout the
dynamics. The resulting ferromagnetic order emerges from the build up of
superpositions of states of maximal total spin. They comprise a decaying

We study the discrimination of weak coherent states of light with significant
overlaps by nondestructive measurements on the light states through measuring
atomic states that are entangled to the coherent states via dipole coupling. In
this way, the problem of measuring and discriminating coherent light states is
shifted to finding the appropriate atom-light interaction and atomic
measurements. We show that this scheme allows us to attain a probability of

Optics naturally provides us with some powerful mathematical operations. Here
we reveal that a single planar interface can compute spatial differentiation to
paraxial coherent beams under oblique incidence. We show that intrinsically the
spatial differentiation results from the spin Hall effect of light with
preparing and postselecting polarization states, in both quantum and classical
levels. Since the spin Hall effect of light is a geometrically protected

The nuclear spin bath (NSB) dynamics and quantum control have primary
significance for the storage and processing of quantum information within a
semiconductor environment. In the presence of a carrier spin, it is the
hyperfine interaction that rules the NSB characteristics. Here, we study the
overall coherence decay and rephasings in hyperfine-driven NSB through the
temporal and spectral behavior of the so-called Loschmidt echo (LE). Unlike
prevailing emphasis on spin-1/2, NSB with larger spin quantum numbers are

We introduce an exact mapping between the Dirac equation in (1+1)-dimensional
curved spacetime (DCS) and a multiphoton quantum Rabi model (QRM). A background
of a (1+1)-dimensional black hole requires a QRM with one- and two-photon terms
that can be implemented in a trapped ion for the quantum simulation of Dirac
particles in curved spacetime. We illustrate our proposal with a numerical
analysis of the free fall of a Dirac particle into a (1+1)-dimensional black

We discuss a surprisingly simple scheme for accounting (and removal) of error
in observables determined from quantum algorithms. A correction to the value of
the observable is calculated by first measuring the observable with all error
sources active and subsequently measuring the observable with each error source
removed separately. We apply this scheme to the variational quantum
eigensolver, simulating the calculation of the ground state energy of
equilibrium H$_2$ and LiH in the presence of several noise sources, including