arXiv subjects

Renato Moreira Angelo

Publications and source records attributed to Renato Moreira Angelo.

5 recordsLinked to original sources

arXiv2026

Energy-space quantum walks: Thermalization without state convergence

We introduce energy-space quantum walks as a minimal framework to investigate equilibration, thermalization, and irreversibility from an effective-dynamics perspective. By mapping the configuration space of a walk onto a ladder of energy eigenlevels, we reinterpret thermalization as transport in energy space, independently of microscopic system--bath details. At the classical level, the resulting birth--death--lazy dynamics leads to equilibration of the energy distribution and, under suitable conditions, to a Gibbs stationary state. We then embed this dynamics into a unitary, collision-assisted model in which coherence is controlled by a single parameter. A central result is a structural decoupling between population dynamics and coherence generation: while the populations evolve according to the classical process and relax to the Gibbs distribution, the full quantum state exhibits a persistent coherence-induced deviation from the thermal manifold. This establishes a minimal scenario of thermalization without state convergence, where equilibration occurs at the level of populations but not at the level of the full density operator. We quantify this effect using the thermal distance to the Gibbs state and derive perturbative bounds that relate the long-time deviation to classical transport properties. Our results show that coherence acts as a controllable and quantitatively bounded source of nonthermal behavior, providing a clear separation between classical equilibration and genuinely quantum corrections.

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arXiv2023

Fluctuation theorems for genuine quantum mechanical regimes

Of indisputable relevance for non-equilibrium thermodynamics, fluctuations theorems have been generalized to the framework of quantum thermodynamics, with the notion of work playing a key role in such contexts. The typical approach consists of treating work as a stochastic variable and the acting system as an eminently classical device with a deterministic dynamics. Inspired by technological advances in the field of quantum machines, here we look for corrections to work fluctuations theorems when the acting system is allowed to enter the quantum domain. This entails including the acting system in the dynamics and letting it share a nonclassical state with the system acted upon. Moreover, favoring a mechanical perspective to this program, we employ a concept of work observable. For simplicity, we choose as theoretical platform the autonomous dynamics of a two-particle system with an elastic coupling. For some specific processes, we derive several fluctuation theorems within both the quantum and classical statistical arenas. In the quantum results, we find that, along with entanglement and quantum coherence, aspects of inertia also play a significant role since they regulate the route to mechanical equilibrium.

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arXiv2021

Quantum resource covariance

The developments of special relativity and quantum mechanics marked the beginning of the modern physics age. The former has taught us that while space and time are frame dependent notions, there is a quantity -- the space-time interval -- whose value all inertial observers agree upon. This reveals, so to speak, a genuine "fact" of the universe, a relativistic invariant. On the other hand, since the dawn of quantum mechanics, there is no consensus on what the theory is all about. The situation is admittedly subtler: quantum theory is grounded on a complex vector space and the very notions of observer and reference frame are controversial. Here we construct a theoretical framework within which a given combination of quantum resources is shown to be a Galilean invariant. To this end, we postulate a principle of relational symmetry between "the observer" and "the observed" and employ the notion of quantum reference frame. Unitary transformations then follow that allow us to perceive the physical resources seen from the viewpoint of any quantum system. Interestingly, we find that one needs more than quantum coherence and quantum correlations to prove quantum resources covariance. Finally, we show that the notion of physical reality implied by quantum mechanics is not absolute.

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arXiv2020

Time Contraction Within Lightweight Reference Frames

The special theory of relativity teaches us that, although distinct inertial frames perceive the same dynamical laws, space and time intervals differ in value. We revisit the problem of time contraction using the paradigmatic model of a fast-moving laboratory within which a photon is emitted and posteriorly absorbed. In our model, however, the laboratory is composed of two independent parallel plates, each of which allowed to be sufficiently light so as to get kickbacks upon emission and absorption of light. We show that the lightness of the laboratory accentuates the time contraction. We also discuss how the photon frequency shifts upon reflection in a light moving mirror. Although often imperceptible, these effects will inevitably exist whenever realistic finite-mass bodies are involved. More fundamentally, they should necessarily permeate any eventual approach to the problem of relativistic quantum frames of reference.

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arXiv2003

Ordered Quantization and the Ehrenfest Time Scale

We propose a prescription to quantize classical monomials in terms of symmetric and ordered expansions of non-commuting operators of a bosonic theory. As a direct application of such quantization rules, we quantize a classically time evolved function $\mathcal{O}(q,p,t)$, and calculate its expectation value in coherent states. The result can be expressed in terms of the application of a classical operator which performs a {\em Gaussian smoothing} of the original function $\mathcal{O}$ evaluated at the center of the coherent state. This scheme produces a natural semi-classical expansion for the quantum expectation values at a short time scale. Moreover, since the classical Liouville evolution of a Gaussian probability density gives the {\bf same} form for the classical statistical mean value, we can calculate the first order correction in $\hbar$ entirely from the associated classical time evolved function. This allows us to write a general expression for the Ehrenfest time in terms of the departure of the centroid of the quantum distribution from the classical trajectory provided we start with an initially coherent state for each subsystem. In order to illustrate this approach, we have calculated analytically the Ehrenfest time of a model with $N$ coupled non-linear oscillators with non-linearity of even order.

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