arXiv subjects

L. F. Alves da Silva

Publications and source records attributed to L. F. Alves da Silva.

6 recordsLinked to original sources

arXiv2026

Quantum simulacra

Here we analyze the creation of quantum simulacra: phenomena that emerge from treating a Hermitian or non-Hermitian quantum system in metrics other than the standard $L^{2}$. Changing the metric redefines the set of system observables and thus the experimental arrangement for their measurement, making quantum contextuality and microscopic reality metric-dependent. The simulacra therefore consist, on the one hand, of a resizing of the status of quantum measurement, which has always occupied a central role in quantum mechanics: beyond the connection between quantum and classical dynamics, measurements performed in an appropriate metric can emulate a microscopic reality distinct from that prescribed by the Hamiltonian. On the other hand, simulacra provide a route to implementing quantum operations that lie beyond the reach of the $L^2$ metric. Quantum simulacra offer, as an example, an explanation for the recent observation of the violation of Bell inequalities with unentangled photons [Sci. Adv. \textbf{11}, eadr1794 (2025)]: photons that are separable in $L^2$ metric, become entangled when analyzed within a new metric framework. Simulacrum comes at the cost of implementing measurements of the metric-redefined observables; to address this challenge, we propose a scheme combining positive operator-valued measures with postselected subensembles.

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arXiv2026

Collective Mpemba-Type Relaxation in Degenerate Bosonic Modes Coupled to a Common Thermal Reservoir

We investigate collective Mpemba-type relaxation in a degenerate family of bosonic modes coupled to a common thermal reservoir. Starting from a fully symmetric M-mode description and employing a representative mean-field reduction, we derive effective master equations for weak-coupling Markovian, strong-coupling Caldeira-Leggett, and weak-coupling non-Markovian regimes. In the weak-coupling Markovian limit, relaxation separates into an incoherent thermal channel decaying at rate gamma and a collective coherent channel decaying at rate M gamma, yielding an explicit Mpemba crossing time determined by the initial-state preparation. In the strong-coupling Caldeira-Leggett regime, transient quadrature dynamics enriches the relaxation pattern, delaying crossings in the overdamped sector and generating multiple crossings in the underdamped sector. In the non-Markovian regime, reservoir memory reshapes the same channel-competition mechanism through time-dependent decay rates and a Lamb shift, producing delayed and clustered crossing windows. Numerical results based on the energy and the Kullback-Leibler divergence reveal Mpemba and anti-Mpemba behavior, criterion dependence, and multiple transient reorderings induced by collective coherence, quadrature dynamics, and reservoir memory.

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arXiv2026

Spontaneous symmetry breaking for nonautonomous pseudo-Hermitian systems

Here we first present an alternative formulation of the Lewis & Riesenfeld theorem for solving the Schrödinger equation with nonautonomous Hermitian and pseudo-Hermitian Hamiltonians. We then employ this framework to characterize the spontaneous breaking of time-dependent antilinear symmetries of these Hamiltonians. We demonstrate that, under unbroken antilinear symmetries, the Lewis & Riesenfeld phases are real and odd functions of time, which allows us to recover the well-known real spectra of time-independent pseudo-Hermitian Hamiltonians. However, in the spontaneously broken regime, imaginary components of the Lewis & Riesenfeld phases arise, leading to coalescence effects analogous to those in the time-independent scenario. Finally, we present an illustrative example of unbroken and broken PT-symmetry for a time-dependent Hamiltonian modeling the non-Hermitian dynamical Casimir effect.

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arXiv2025

Superradiance in dense atomic samples

Here we present an approach to the problem of superradiance in dense atomic samples, when dipolar interactions arise between atoms. Our treatment consists of the sequential use of the Holstein-Primakoff and mean-field approximations, from which we derive master equations for the strong and weak couplings of the sample with the reservoir. We find, in both cases, that the radiation emission presents remarkable features, with characteristic emission times much shorter and intensities much higher than those of Dicke superradiance. In particular, for strong sample-reservoir coupling, a whole comb of superpulses occurs within an envelope with the above-mentioned characteristic emission times much shorter and intensities much higher than those of Dicke superradiance.

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arXiv2025

Superradiance and Superabsorption Engine of $N$ Two-Level Systems: $N^{2}$-Power Scaling at Near-Unity Efficiency

We present a thermal engine that exploits the \emph{cooperative superradiance} and \emph{superabsorption} of a sample of $N$ two-level atoms. This engine operates using a single cold reservoir via cycles of collective pumping followed by decay. Using an effective mean-field Hamiltonian to describe the many-body dynamics, we design optimized drive pulses that preserve adiabaticity and achieve an average power output scaling quadratically with the system size, $P \propto N^2$. An experimentally measurable figure of merit demonstrates that the efficiency of this superengine can approach unity. The resulting analytical model, which yields a representative Hamiltonian for the sample within the mean-field formalism, is validated by numerical simulations. Our results pave the way for scalable and highly efficient quantum heat engines based on collective effects.

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arXiv2025

Coherent deflection of atomic samples and positional mesoscopic superpositions

We present a protocol based on the interplay between superradiance and superabsorption to achieve the coherent deflection of an atomic sample due to the momentum transfer from the atoms to a cavity field. The coherent character of this momentum transfer, causing the atomic sample to deflect as a whole, follows from the collective nature of the atomic superradiant pulse and its superabsorption by the cavity field. The protocol is then used for the construction of positional mesoscopic atomic superpositions.

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