arXiv subjects

Stefano Marcantoni

Publications and source records attributed to Stefano Marcantoni.

15 recordsLinked to original sources

arXiv2026

On spatial decoherence in many-body systems

We study the dynamics of a many-body quantum system strongly interacting with a bosonic reservoir. The coupling is given by a potential operator for the system and it is linear in the field. We show that in the limit of infinite coupling strength the system undergoes instantaneous spatial decoherence. To resolve the decoherence process in time we consider large coupling strengths $\lambda$ and short times scaling as $t\propto \lambda^{-\alpha}$, with $\alpha\ge0$, in the limit $\lambda\rightarrow\infty$. On short time scales $\alpha>1$ the dynamics is trivial while on longer ones $0\le\alpha<1$ the decoherence is instantaneous. We show that the decoherence process is resolved exactly for $\alpha=1$, defining the fine-grained time scale $\tau=\lambda t$. We construct an approximate effective evolution map of the many-body system with controlled error estimates. Generically, the effective dynamics is markovian, but not given by a dynamical semigroup. As a physical application we give a rigorous description of the phenomenon of localization of macroscopic quantum objects in position space.

math-ph↗

arXiv2026

Ultrastrongly coupled open systems and fine grained time

We study the dynamics of a d-level quantum system coupled to a bosonic reservoir when the coupling constant is large. It is known that in the limit of infinite coupling strength, the system undergoes an instantaneous nonselective measurement, resulting in the immediate decoherence in the measurement basis, followed by a unitary Zeno dynamics. Here we resolve this dynamical process by introducing a fine grained scaling regime of short times proportional to the inverse coupling. We provide a rigorous derivation of the open system dynamics in this regime of ultrastrong coupling and demonstrate how decoherence unfolds continuously in the new time scale. We show that Markovian dynamics which are not given by semigroups arise naturally, in contrast to what happens in the weak coupling theory.

quant-ph↗

arXiv2025

Fluctuation Relations associated to an arbitrary bijection in path space

We introduce a framework to identify Fluctuation Relations for vector-valued observables in physical systems evolving through a stochastic dynamics. These relations arise from the particular structure of a suitable entropic functional and are induced by transformations in trajectory space that are invertible but are not involutions, typical examples being spatial rotations and translations. In doing so, we recover as particular cases results known in the literature as isometric fluctuation relations or spatial fluctuation relations and moreover we provide a recipe to find new ones. We mainly discuss two case studies, namely stochastic processes described by a canonical path probability and non degenerate diffusion processes. In both cases we provide sufficient conditions for the fluctuation relation to hold, considering either finite time or asymptotically large times.

cond-mat.stat-mech↗

arXiv2024

Ultrastrong coupling, nonselective measurement and quantum Zeno dynamics

We study the dynamics of an open quantum system linearly coupled to a bosonic reservoir. We show that, in the ultrastrong coupling limit, the system undergoes a nonselective measurement and then evolves unitarily according to an effective Zeno Hamiltonian. This dynamical process is largely independent of the reservoir state. We examine the entanglement breaking effect of the ultrastrong coupling on the system. We also derive the evolution equation for systems in contact with several reservoirs when one coupling is ultrastrong. The effective system dynamics displays a rich structure and, contrarily to the single reservoir case, it is generally non-Markovian. Our approach is based on a Dyson series expansion, in which we can take the ultrastrong limit termwise, and a subsequent resummation of the series. Our derivation is mathematically rigorous and uncomplicated.

quant-ph↗

arXiv2023

Dynamics of mean-field Fermi systems with nonzero pairing

We study the dynamics of many-body Fermi systems, for a class of initial data which are close to quasi-free states exhibiting a nonvanishing pairing matrix. We focus on the mean-field scaling, which for fermionic systems is naturally coupled with a semiclassical scaling. Under the assumption that the initial datum enjoys a suitable semiclassical structure, we give a rigorous derivation of the time-dependent Hartree-Fock-Bogoliubov equation, a nonlinear effective evolution equation for the one-particle density matrix of the system, as the number of particles goes to infinity. Our result holds for all macroscopic times, and provides bounds for the rate of convergence.

math-ph↗

arXiv2023

Stochastic entropy production: Fluctuation relation and irreversibility mitigation in non-unital quantum dynamics

In this work, we study the stochastic entropy production in open quantum systems whose time evolution is described by a class of non-unital quantum maps. In particular, as in [Phys. Rev. E 92, 032129 (2015)], we consider Kraus operators that can be related to a nonequilibrium potential. This class accounts for both thermalization and equilibration to a non-thermal state. Unlike unital quantum maps, non-unitality is responsible for an unbalance of the forward and backward dynamics of the open quantum system under scrutiny. Here, concentrating on observables that commute with the invariant state of the evolution, we show how the non-equilibrium potential enters the statistics of the stochastic entropy production. In particular, we prove a fluctuation relation for the latter and we find a convenient way of expressing its average solely in terms of relative entropies. Then, the theoretical results are applied to the thermalization of a qubit with non-Markovian transient, and the phenomenon of irreversibility mitigation, introduced in [Phys. Rev. Research 2, 033250 (2020)], is analyzed in this context.

quant-ph↗

arXiv2022

Anderson and many-body localization in the presence of spatially correlated classical noise

We study the effect of spatially correlated classical noise on both Anderson and many-body localization of a disordered fermionic chain. By analyzing the evolution of the particle density imbalance following a quench from an initial charge density wave state, we find prominent signatures of localization also in the presence of the time-dependent noise, even though the system eventually relaxes to the infinite temperature state. In particular, for sufficiently strong static disorder we observe the onset of metastability, which becomes more prominent the stronger the spatial correlations of the noise. In this regime we find that the imbalance decays as a stretched-exponential - a behavior characteristic of glassy systems. We identify a simple scaling behavior of the relevant relaxation times in terms of the static disorder and of the noise correlation length. We discuss how our results could be exploited to extract information about the localization length in experimental setups.

cond-mat.dis-nn↗

arXiv2021

Moiré patterns generated by stacked 2D lattices: a general algorithm to identify primitive coincidence cells

Two-dimensional materials on metallic surfaces or stacked one on top of the other can form a variety of moiré superstructures depending on the possible parameter and symmetry mismatch and misorientation angle. In most cases, such as incommensurate lattices or identical lattices but with a small twist angle, the common periodicity may be very large, thus making numerical simulations prohibitive. We propose here a general procedure to determine the minimal simulation cell which approximates, within a certain tolerance and a certain size, the primitive cell of the common superlattice, given the two interfacing lattices and the relative orientation angle. As case studies to validate our procedure, we report two applications of particular interest: the case of misaligned hexagonal/hexagonal identical lattices, describing a twisted graphene bilayer or a graphene monolayer grown on Ni(111), and the case of hexagonal/square lattices, describing for instance a graphene monolayer grown on Ni(100) surface. The first one, which has also analytic solutions, constitutes a solid benchmark for the algorithm; the second one shows that a very nice description of the experimental observations can be obtained also using the resulting relatively small coincidence cells.

cond-mat.mtrl-sci↗

arXiv2021

Symmetry-induced fluctuation relations in open quantum systems

We derive a general scheme to obtain quantum fluctuation relations for dynamical observables in open quantum systems. For concreteness we consider Markovian non-unitary dynamics that is unraveled in terms of quantum jump trajectories, and exploit techniques from the theory of large deviations like the tilted ensemble and the Doob transform. Our results here generalise to open quantum systems fluctuation relations previously obtained for classical Markovian systems, and add to the vast literature on fluctuation relations in the quantum domain, but without resorting to the standard two-point measurement scheme. We illustrate our findings with three examples in order to highlight and discuss the main features of our general result.

quant-ph↗

arXiv2020

Irreversibility mitigation in unital non-Markovian quantum evolutions

The relation between the thermodynamic entropy production and non-Markovian evolutions is matter of current research. Here, we study the behavior of the stochastic entropy production in open quantum systems undergoing unital non-Markovian dynamics. In particular, for the family of Pauli channels we show that in some specific time intervals both the average entropy production and the variance can decrease, provided that the quantum dynamics fails to be P-divisible. Although the dynamics of the system is overall irreversible, our result may be interpreted as a transient tendency towards reversibility, described as a delta peaked distribution of entropy production around zero. Finally, we also provide analytical bounds on the parameters in the generator giving rise to the quantum system dynamics, so as to ensure irreversibility mitigation of the corresponding non-Markovian evolution.

quant-ph↗

arXiv2020

Symmetry-induced fluctuation relations for dynamical observables irrespective of their behaviour under time-reversal

We extend previous work to describe a class of fluctuation relations (FRs) that emerge as a consequence of symmetries at the level of stochastic trajectories in Markov chains. We prove that given such a symmetry, and for a suitable dynamical observable, it is always possible to obtain a FR under a biased dynamics corresponding to the so-called generalized Doob transform. The general transformations of the dynamics that we consider go beyond time-reversal or spatial isometries, and an implication is the existence of FRs for observables irrespective of their behaviour under time-reversal, for example for time-symmetric observables rather than currents. We further show how to deduce in the long-time limit these FRs from the symmetry properties of the generator of the dynamics. We illustrate our results with four examples that highlight the novel features of our work.

cond-mat.stat-mech↗

arXiv2020

Vibrational coherent control of localized d-d electronic excitation

Addressing the role of quantum coherence in the interplay between the different matter constituents (electrons, phonons and spin) is a critical step towards understanding transition metal oxides and design complex materials with new functionalities. Here we use coherent vibrational control of onsite d-d electronic transitions in a model edge-sharing insulating transition metal oxide (CuGeO3) to single-out the effects of vibrational coherence in electron-phonon coupling. By comparing time domain experiments based on high and low frequency ultrashort pumps with a fully quantum description of phonon assisted absorption, we could distinguish the processes associated to incoherent thermal lattice fluctuations from those driven by the coherent motion of the atoms. In particular, while thermal fluctuation of the phonon bath uniformly increases the electronic absorption, the resonant excitation of phonon modes results also in light-induced transparency which is coherently controlled by the vibrational motion.

cond-mat.mtrl-sci↗

arXiv2019

Quantum model for Impulsive Stimulated Raman Scattering

The interaction between ultrashort light pulses and non-absorbing materials is dominated by Impulsive Stimulated Raman Scattering (ISRS). The description of ISRS in the context of pump\&probe experiments is based on effective classical models describing the interaction between the phonon and pulsed electromagnetic fields. Here we report a theoretical description of ISRS where we do not make any semi-classical approximation and we treat both photonic and phononic degrees of freedom at the quantum level. The results of the quantum model are compared with semiclassical results and validated by means of spectrally resolved pump\&probe measurements on $α$-quartz.

quant-ph↗

arXiv2019

Impact of nonideal cycles on the efficiency of quantum heat engines

Given a quantum heat engine that operates in a cycle that reaches maximal efficiency for a time-dependent Hamiltonian H(t) of the working substance, with overall controllable driving H(t) = g(t) H, we study the deviation of the efficiency from the optimal value due to a generic time-independent perturbation in the Hamiltonian. We show that for a working substance consisting of two two-level systems, by suitably tuning the interaction, the deviation can be suppressed up to the third order in the perturbation parameter-and thus almost retaining the optimality of the engine.

quant-ph↗

arXiv2019

Qubit Entanglement generation by Gaussian non-Markovian dynamics

We consider two qubits interacting with a common bosonic bath, but not directly between themselves. We derive the (bipartite) entanglement generation conditions for Gaussian non-Markovian dynamical maps and show that they are similar as in the Markovian regime; however, they depend on different physical coefficients and hold on different time scales. Indeed, for small times, in the non-Markovian regime entanglement is possibly generated on a shorter time scale ($\propto t^2$) than in the Markovian one ($\propto t$). Moreover, although the singular coupling limit of non-Markovian dynamics yields Markovian ones, we show that the same limit does not lead from non-Markovian entanglement generation conditions to Markovian ones. Also, the entanglement generation conditions do not depend on the initial time for non-Markovian open dynamics resulting from couplings to bosonic Gaussian baths, while they may depend on time for open dynamics originated by couplings to classical, stochastic Gaussian environments.

quant-ph↗