# All

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