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

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.Comment: 16 pages, 7 figure

Stabilization of quantum metastable states by dissipation

Normally, quantum fluctuations enhance the escape from metastable states in the presence of dissipation. Here we show that dissipation can enhance the stability of a quantum metastable system, consisting of a particle moving in a strongly asymmetric double well potential, interacting with a thermal bath. We find that the escape time from the metastable state has a nonmonotonic behavior versus the system-bath coupling and the temperature, producing a stabilizing effect.Comment: 4 pages, 3 figures, submitted to Phys. Rev.

Quantum resonant activation

Quantum resonant activation is investigated for the archetype setup of an externally driven two-state (spin-boson) system subjected to strong dissipation by means of both analytical and extensive numerical calculations. The phenomenon of resonant activation emerges in the presence of either randomly fluctuating or deterministic periodically varying driving fields. Addressing the incoherent regime, a characteristic minimum emerges in the mean first passage time to reach an absorbing neighboring state whenever the intrinsic time scale of the modulation matches the characteristic time scale of the system dynamics. For the case of deterministic periodic driving, the first passage time probability density function (pdf) displays a complex, multi-peaked behavior, which depends crucially on the details of initial phase, frequency, and strength of the driving. As an interesting feature we find that the mean first passage time enters the resonant activation regime at a critical frequency $\nu^*$ which depends very weakly on the strength of the driving. Moreover, we provide the relation between the first passage time pdf and the statistics of residence times.Comment: 14 pages, 13 figure

IGR J19294+1816: a new Be-X ray binary revealed through infrared spectroscopy

The aim of this work is to characterize the counterpart to the INTEGRAL High Mass X-ray Binary candidate IGR J19294+1816 so as to establish its true nature. We obtained H band spectra of the selected counterpart acquired with the NICS instrument mounted on the Telescopio Nazionale Galileo (TNG) 3.5-m telescope which represents the first infrared spectrum ever taken of this source. We complement the spectral analysis with infrared photometry from UKIDSS, 2MASS, WISE and NEOWISE databases. We classify the mass donor as a Be star. Subsequently, we compute its distance by properly taking into account the contamination produced by the circumstellar envelope. The findings indicate that IGR J19294+1816 is a transient source with a B1Ve donor at a distance of $d = 11 \pm 1$ kpc, and luminosities of the order of $10^{36-37}$ erg s$^{-1}$, displaying the typical behaviour of a Be X-ray binary.Comment: 8 pages, 6 figures, accepted to be published in MNRA

Investigation of soft matter nanomechanics by atomic force microscopy and optical tweezers: a comprehensive review

Soft matter exhibits a multitude of intrinsic physico-chemical attributes. Their mechanical properties are crucial characteristics to define their performance. In this context, the rigidity of these systems under exerted load forces is covered by the field of biomechanics. Moreover, cellular transduction processes which are involved in health and disease conditions are significantly affected by exogenous biomechanical actions. In this framework, atomic force microscopy (AFM) and optical tweezers (OT) can play an important role to determine the biomechanical parameters of the investigated systems at the single-molecule level. This review aims to fully comprehend the interplay between mechanical forces and soft matter systems. In particular, we outline the capabilities of AFM and OT compared to other classical bulk techniques to determine nanomechanical parameters such as Young’s modulus. We also provide some recent examples of nanomechanical measurements performed using AFM and OT in hydrogels, biopolymers and cellular systems, among others. We expect the present manuscript will aid potential readers and stakeholders to fully understand the potential applications of AFM and OT to soft matter systems

Asymptotic Floquet states of a periodically driven spin-boson system in the nonperturbative coupling regime

As a paradigmatic model of open quantum system, the spin-boson model is widely used in theoretical and experimental investigations. Beyond the weak coupling limit, the spin dynamics can be described by a time-nonlocal generalized master equation with a memory kernel accounting for the dissipative effects induced by the bosonic environment. When the spin is additionally modulated by an external time-periodic electromagnetic field, the interplay between dissipation and modulations yields a spectrum of nontrivial asymptotic states, especially in the regime of nonlinear response. Here we implement a method for the evaluation of Floquet dynamics in non-Markovian systems [L. Magazz\`u et al., Phys. Rev. A 96, 042103 (2017)] to find these strongly non-equilibrium states.Comment: 20 pages, 4 figure