# All

Non-Hermitian systems with parity-time symmetry have been developed rapidly

and hold great promise for future applications. Unlike most existing works

considering the symmetry of the free energy terms (e.g., gain-loss system), in

this paper, we report that a realizable non-Hermitian interaction between two

quantum resonances can also have a real spectrum after the exceptional point.

That phenomenon is similar with that in the gain-loss system so that the

Steady-state plasmonic lasing is studied theoretically for a system

consisting of many dye molecules arranged regularly around a gold nano-sphere.

A three-level model with realistic molecular dissipation is employed to analyze

the performance as function of the pump field amplitude and number of

molecules. Few molecules and moderate pumping produce a single narrow emission

peak because the excited molecules transfer energy to a single dipole plasmon

mode by amplified spontaneous emission. Under strong pumping, the single peak

In this review, we provide an introduction and overview to some more recent

advances in real-time dynamics of quantum impurity models and their

realizations in quantum devices. We focus on the Ohmic spin-boson and related

models, which describes a single spin-1/2 coupled to an infinite collection of

harmonic oscillators. The topics are largely drawn from our efforts over the

past years, but we also present a few novel results. In the first part of this

Single-mode Josephson junction-based parametric amplifiers are often modeled

as perfect amplifiers and squeezers. We show that, in practice, the gain,

quantum efficiency, and output field squeezing of these devices are limited by

usually neglected higher-order corrections to the idealized model. To arrive at

this result, we derive the leading corrections to the lumped-element Josephson

parametric amplifier of three common pumping schemes: monochromatic current

Quantum interference is at the heart of what sets the quantum and classical

worlds apart. We demonstrate that quantum interference effects involving a

many-body working medium is responsible for genuinely non-classical features in

the performance of a quantum heat engine. The features with which quantum

interference manifests itself in the work output of the engine depends strongly

on the extensive nature of the working medium. While identifying the class of

In the present article we extend our study (BJP 45 (2015) 369) of generalized

coherent states (GCS) of a one-dimensional particle considering such important

physical system as a 3-dimensional charged particle in electric and magnetic

fields. Constructing GCS in many-dimensional case, we meet nontrivial technical

complications that make the consideration nontrivial and instructive. The GCS

of a system under consideration are constructed. We study properties of these

The adiabatic theorem is a fundamental result established in the early days

of quantum mechanics, which states that a system can be kept arbitrarily close

to the instantaneous ground state of its Hamiltonian if the latter varies in

time slowly enough. The theorem has an impressive record of applications

ranging from foundations of quantum field theory to computational recipes in

molecular dynamics. In light of this success it is remarkable that a

practicable quantitative understanding of what "slowly enough" means is limited

Parallel Lives (PL) is an ontological model of nature in which quantum

mechanics and special relativity are unified in a single universe with a single

space-time. Point-like objects called lives are the only fundamental objects in

this space-time, and they propagate at or below c, and interact with one

another only locally at point-like events in space-time. The only causes and

effects in the universe occur when lives meet locally, and thus the causal

structure of interaction events in space-time is Lorentz invariant. Each life

We generalize the theory of nuclear decay and capture of Gamow that is based

on tunneling through the barrier and internal oscillations inside the nucleus.

In our formalism an additional factor is obtained, which describes distribution

of the wave function of the $\alpha$ particle inside the nuclear region. We

discover new most stable states (called quasibound states) of the compound

nucleus (CN) formed during the capture of $\alpha$ particle by the nucleus.

We consider superconducting circuits for the purpose of simulating the

spin-boson model. The spin-boson model consists of a single two-level system

coupled to bosonic modes. In most cases, the model is considered in a limit

where the bosonic modes are sufficiently dense to form a continuous spectral

bath. A very well known case is the Ohmic bath, where the density of states

grows linearly with the frequency. In the limit of weak coupling or large

temperature, this problem can be solved numerically. If the coupling is strong,