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Roberto Romo

Publications and source records attributed to Roberto Romo.

10 recordsLinked to original sources
arXiv2024

Transient concurrence for copropagating entangled bosons and fermions

The transient dynamics of copropagating entangled bosons and fermions remain an unexplored aspect of quantum mechanics. We investigate how entanglement manifests itself in the spatiotemporal evolution of the particles using a modified version of the quantum shutter model. We derive a transient concurrence as a dynamical indicator of entanglement and demonstrate that it modulates the interference structure of the joint probability density, thereby revealing the spatial and temporal regions where probabilistic bunching and antibunching phenomena emerge. Furthermore, we derive analytical expressions revealing a structural connection between concurrence and the cosine modulation characteristic of Hanbury-Brown and Twiss (HBT) interference patterns. In the stationary limit, the Wootters concurrence is shown to coincide with the interferometric visibility of the resulting pattern. This work establishes a structural bridge between entanglement signatures and interference phenomena in transient copropagating systems, providing a theoretical framework for exploring their dynamical interplay.

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arXiv2019

Effect of the resonance spectra in the propagation of two decaying entangled particles

An exact analytical solution of the decaying wave function of two identical noninteracting particles, which are entangled by spatial symmetry, is used to analyze the effect of the resonance spectra in the propagation of the decaying probability density outside the interaction potential region. We find, using exactly solvable problems, that a usual approximation that considers the two resonance levels associated with the initial states, is affected substantially in the case of sharp high energy resonances by disrupting the pure exponential decaying regime exhibited by the two resonance level approximation, whereas for broad high energy resonances, we find that the probability density profile is well described by the two resonance approximation.

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arXiv2019

The exponential-nonexponential transition in quantum decay as a phenomenon of interference in time domain of the decaying particle with itself

By using an exact analytical non-Hermitian approach in terms of resonance (quasinormal) states we express the decaying wave function as the sum of exponential and nonexponential decaying solutions to the time-dependent Schrödinger equation. We show that the exponential-nonexponential transition of decay at long times represents physically a process of interference in time domain of the decaying particle with itself.

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arXiv2017

Nonexponential tunneling decay of a single ultracold atom

By using an exact analytical approach to the time evolution of decay we investigate the tunneling decay of ultracold single atoms, to discuss the conditions for deviations of the exponential decay law. We find that $R$, given by the ratio of the energy of the decaying fragment $\mathcal{E}_r$ to its corresponding width $Γ_r$, is the relevant quantity in this study. When $R$ is less than $0.3$ the decay of the atom goes to a good approximation for the first few lifetimes as $\exp(-Γ_rt/2\hbar)t^{-3/2}$. We also find that for values of $R \sim 1$, the nonexponential behavior occurs in a post-exponential regime that goes as $t^{-3}$ after around a dozen of lifetimes. The above conditions depend on suitable designed potential parameters and suggest that for values $R \lesssim 1$, the experimental verification of nonexponential decay might be possible.

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arXiv2002

The role of the buildup oscillations on the speed of resonant tunneling diodes

The fastest tunneling response in double barrier resonant structures is investigated by considering explicit analytic solutions of the time dependent Schrödinger equation. For cutoff initial plane waves, we find that the earliest tunneling events consist on the emission of a series of propagating pulses of the probability density governed by the buildup oscillations in the quantum well. We show that the fastest tunneling response comes from the contribution of incident carriers at energies different from resonance, and that its relevant time scale is given by $τ_r=π\hbar /| E-ε| $, where $ε$ is the resonance energy and $E$ is the incidence energy.

quant-ph↗
arXiv2002

Quantum-wave evolution in a step potential barrier

By using an exact solution to the time-dependent Schrödinger equation with a point source initial condition, we investigate both the time and spatial dependence of quantum waves in a step potential barrier. We find that for a source with energy below the barrier height, and for distances larger than the penetration length, the probability density exhibits a {\it forerunner} associated with a non-tunneling process, which propagates in space at exactly the semiclassical group velocity. We show that the time of arrival of the maximum of the {\it forerunner} at a given fixed position inside the potential is exactly the traversal time, $τ$. We also show that the spatial evolution of this transient pulse exhibits an invariant behavior under a rescaling process. This analytic property is used to characterize the evolution of the {\it forerunner}, and to analyze the role played by the time of arrival, $3^{-1/2}τ$, found recently by Muga and Büttiker [Phys. Rev. A {\bf 62}, 023808 (2000)].

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arXiv2002

Transient tunneling effects of resonance doublets in triple barrier systems

Transient tunneling effects in triple barrier systems are investigated by considering a time-dependent solution to the Schrödinger equation with a cutoff wave initial condition. We derive a two-level formula for incidence energies $E$ near the first resonance doublet of the system. Based on that expression we find that the probability density along the internal region of the potential, is governed by three oscillation frequencies: one of them refers to the well known Bohr frequency, given in terms of the first and second resonance energies of the doublet, and the two others, represent a coupling with the incidence energy $E$. This allows to manipulate the above frequencies to control the tunneling transient behavior of the probability density in the short-time regime

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arXiv2000

Dynamical analysis of the buildup process near resonance

The time evolution of the buildup process inside a double-barrier system for off-resonance incidence energies is studied by considering the analytic solution of the time dependent Schrödinger equation with cutoff plane wave initial conditions. We show that the buildup process exhibits invariances under arbitrary changes on the system parameters, which can be successfully described by a simple and easy-to-use one-level formula. We find that the buildup of the off-resonant probability density is characterized by an oscillatory pattern modulated by the resonant case which governs the duration of the transient regime. This is evidence that off-resonant and resonant tunneling are two correlated processes, whose transient regime is characterized by the same transient time constant of two lifetimes.

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arXiv2000

Dynamical description of the buildup process in resonant tunneling: Evidence of exponential and non-exponential contributions

The buildup process of the probability density inside the quantum well of a double-barrier resonant structure is studied by considering the analytic solution of the time dependent Schrödinger equation with the initial condition of a cutoff plane wave. For one level systems at resonance condition we show that the buildup of the probability density obeys a simple charging up law, $| Ψ(τ) / ϕ| =1-e^{-τ/τ_0},$ where $ϕ$ is the stationary wave function and the transient time constant $τ_0$ is exactly two lifetimes. We illustrate that the above formula holds both for symmetrical and asymmetrical potential profiles with typical parameters, and even for incidence at different resonance energies. Theoretical evidence of a crossover to non-exponential buildup is also discussed.

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