Search results for "Quantum"

Quantum dissipative dynamics of a bistable system in the sub-Ohmic to super-Ohmic regime

2016

We investigate the quantum dynamics of a multilevel bistable system coupled to a bosonic heat bath beyond the perturbative regime. We consider different spectral densities of the bath, in the transition from sub-Ohmic to super-Ohmic dissipation, and different cutoff frequencies. The study is carried out by using the real-time path integral approach of the Feynman-Vernon influence functional. We find that, in the crossover dynamical regime characterized by damped \emph{intrawell} oscillations and incoherent tunneling, the short time behavior and the time scales of the relaxation starting from a nonequilibrium initial condition depend nontrivially on the spectral properties of the heat bath.

A Stochastic Approach to Quantum Statistics Distributions: Theoretical Derivation and Monte Carlo Modelling

2009

Abstract. We present a method aimed at a stochastic derivation of the equilibrium distribution of a classical/quantum ideal gas in the framework of the canonical ensemble. The time evolution of these ideal systems is modelled as a series of transitions from one system microstate to another one and thermal equilibrium is reached via a random walk in the single-particle state space. We look at this dynamic process as a Markov chain satisfying the condition of detailed balance and propose a variant of the Monte Carlo Metropolis algorithm able to take into account indistinguishability of identical quantum particles. Simulations performed on different two-dimensional (2D) systems are revealed to…

Hot-electron noise suppression in n-Si via the Hall effect

2008

We investigate how hot-electron fluctuations in n-type Si are affected by the presence of an intense (static) magnetic field in a Hall geometry. By using the Monte Carlo method, we find that the known Hall-effect-induced redistribution of electrons among valleys can suppress electron fluctuations with a simultaneous enhancement of the drift velocity. We investigate how hot-electron fluctuations in n-type Si are affected by the presence of an intense (static) magnetic field in a Hall geometry. By using the Monte Carlo method, we find that the known Hall-effect-induced redistribution of electrons among valleys can suppress electron fluctuations with a simultaneous enhancement of the drift vel…

Localization in a QFT Model

2006

Localization properties of a QFT model, consisting of a quantum scalar field interacting linearly with a classical localized source, are investigated using various approaches present in the literature. We evaluate, to any order of the field–matter coupling constant, the time evolution of average values of one-point localization observables and scalar product between the quantum field state of the evolving system and localized states. We show that the appearance of nonlocality can be connected to nonlocal properties of localized states used or to the fact that localization operators do not satisfy the microcausality principle and therefore does not imply the violation of causality.

Step-by-Step Control of the Dynamics of a Superconducting QED-like System

2007

We discuss the modus operandi of a theoretical scalable coupling scheme to control step by step the time evolution of a pair of flux qubits embedded in a lossy resonant cavity. The sequential interaction of each qubit with the quantized cavity mode is controlled by externally applied magnetic fluxes. Our analysis indicates that indirect qubit-qubit interactions, with the electromagnetic mode acting as a data bus, can be selectively performed and exploited both for the implementation of entangling gates and for the generation of states with a priori known characteristics.

Erratum: Partition function of the trigonometric SOS model with reflecting end

2010

Weak pseudo-bosons

2020

We show how the notion of {\em pseudo-bosons}, originally introduced as operators acting on some Hilbert space, can be extended to a distributional settings. In doing so, we are able to construct a rather general framework to deal with generalized eigenvectors of the multiplication and of the derivation operators. Connections with the quantum damped harmonic oscillator are also briefly considered.

Tridiagonality, supersymmetry and non self-adjoint Hamiltonians

2019

In this paper we consider some aspects of tridiagonal, non self-adjoint, Hamiltonians and of their supersymmetric counterparts. In particular, the problem of factorization is discussed, and it is shown how the analysis of the eigenstates of these Hamiltonians produce interesting recursion formulas giving rise to biorthogonal families of vectors. Some examples are proposed, and a connection with bi-squeezed states is analyzed.

Large systems of path-repellent Brownian motions in a trap at positive temperature

2006

We study a model of $ N $ mutually repellent Brownian motions under confinement to stay in some bounded region of space. Our model is defined in terms of a transformed path measure under a trap Hamiltonian, which prevents the motions from escaping to infinity, and a pair-interaction Hamiltonian, which imposes a repellency of the $N$ paths. In fact, this interaction is an $N$-dependent regularisation of the Brownian intersection local times, an object which is of independent interest in the theory of stochastic processes. The time horizon (interpreted as the inverse temperature) is kept fixed. We analyse the model for diverging number of Brownian motions in terms of a large deviation princip…

Quantum averaging for driven systems with resonances

2000

Abstract We discuss the effects of resonances in driven quantum systems within the context of quantum averaging techniques in the Floquet representation. We consider in particular iterative methods of KAM type and the extensions needed to take into account resonances. The approach consists in separating the coupling terms into resonant and nonresonant components at a given scale of time and intensity. The nonresonant part can be treated with perturbative techniques, which we formulate in terms of KAM-type unitary transformations that are close to the identity. These can be interpreted as averaging procedures with respect to the dynamics defined by effective uncoupled Hamiltonians. The reson…