arXiv subjects

L. Morales-Molina

Publications and source records attributed to L. Morales-Molina.

9 recordsLinked to original sources

arXiv2026

Enhancing supercurrent-based inertial sensing via interactions in atomtronic angular accelerometers

We theoretically investigate supercurrents of ultracold atoms in angularly ac-shaken ring lattices subjected to external rotation. Our results demonstrate how these supercurrents can be harnessed for the development of high-precision atomtronic angular accelerometers. Using both analytical and numerical approaches within the Bose-Hubbard model framework, we demonstrate that a significant net atomic current arises when the lattice driving frequency is tuned to an integer fraction of the Bloch frequency, while the current averages to nearly zero away from such a resonance. In the single-particle regime, the resonance width scales inversely with the averaging time, thereby setting a fundamental Fourier-limited bound on the measurement's sensitivity. Strikingly, our numerical simulations demonstrate that this Fourier limit - a fundamental barrier in the non-interacting system - can be surpassed by introducing weak interactions between atoms. In the interacting regime, the sensitivity surpasses the Fourier-limited scaling with the averaging time, achieving an improvement of at least two orders of magnitude over the single-particle scenario, and exceeding the performance of previously proposed ultracold-atom-based angular accelerometers. These findings pave the way for developing new atomic-current-based inertial sensors with interaction-enhanced sensitivity.

cond-mat.quant-gas↗

arXiv2014

Resonant metallic states in driven quasiperiodic lattices

We consider a quasiperiodic Aubry-Andre (AA) model and add a weak time-periodic and spatially quasiperiodic perturbation. The undriven AA model is chosen to be well in the insulating regime. The spatial quasiperiodic perturbation extends the model into two dimensions in reciprocal space. For a spatial resonance which reduces the reciprocal space dynamics to an effective one-dimensional two-leg ladder case, the ac perturbation resonantly couples certain groups of localized eigenstates of the undriven AA model and turns them into extended metallic ones. Slight detuning of the spatial and temporal frequencies off resonance returns these states into localized ones. We analyze the details of the resonant metallic eigenstates using Floquet representations. In particular, we find that their size grows linearly with the system size. Initial wave packets overlap with resonant metallic eigenstates and lead to ballistic spreading.

cond-mat.dis-nn↗

arXiv2012

Current and entanglement in a Bose-Hubbard lattice

We study the generation of entanglement for interacting cold atoms in an optical lattice. The entanglement is generated by managing the interaction between two distinct atomic species. It is found that the current of one of the species can be used as a good indicator of entanglement generation. The thermalization process between the species is also shown to be closely related to the evolution of the current.

cond-mat.quant-gas↗

arXiv2011

Non-adiabatic transitions in a non-symmetric optical lattice

We study Landau-Zener interband transitions for a non-symmetric optical lattice in the presence of an external force. We show that gain and losses of the light beam, as well as the relative occupation probabilities of the bands involved in the transitions can be accurately managed upon tuning the amplitude of the non-Hermitian component of the lattice. Exact expressions for the transition and non-transition probabilities for a non-symmetric system obtained within a two-mode approximation are provided. These equations successfully account for the main features of the transitions in the optical lattice. We also interpret the non-conventional Bloch oscillations at criticality studied in Phys. Rev. Lett. 103, 123601 (2009) as a series of a Landau-Zener transitions.

quant-ph↗

arXiv2010

Accurate control of a Bose-Einstein condensate by managing the atomic interaction

We exploit the variation of the atomic interaction in order to move ultra-cold atoms across an AC-driven periodic lattice. By breaking relevant symmetries, a gathering of atoms is achieved. Accurate control of the gathered atoms positions can be demonstrated via the control of the atomic localization process. The localization process is analyzed with the help of the nonlinear Floquet states where the Landau-Zener tunneling between states is observed and controlled. Transport effects in the presence of disorder are discussed.

nlin.PS↗

arXiv2008

Quantum ratchet control - harvesting on Landau-Zener transitions

We control the current of a single particle quantum ratchet by designing ramping schemes for experimentally accessible control parameters. We harvest on Landau-Zener transitions between Floquet states. Adiabatic and diabatic ramping allow to control the resulting directed transport. We find strong changes of the current in the adiabatic regime. Simple loops in control parameter space with alternating adiabatic and diabatic ramping are proposed. We obtain also current reversal. Full desymmetrization of the quantum ratchet increases the critical ramping speed which separates the adiabatic from the diabatic regime.

cond-mat.other↗

arXiv2007

Periodically driven Quantum Ratchets: Symmetries and Resonances

We study the quantum version of a tilting and flashing Hamiltonian ratchets, consisting of a periodic potential and a time-periodic driving field. The system dynamics is governed by a Floquet evolution matrix bearing the symmetry of the corresponding Hamiltonian. The dc-current appears due to the desymmetrization of Floquet eigenstates, which become transporting when all the relevant symmetries are violated. Those eigenstates which mostly contribute to a directed transport reside in phase space regions corresponding to classical resonances. Quantum dynamics leads to the dependence of the average velocity on the initial phase of the ac-field. A resonant enhancement (or suppression) of the dc-current, due to avoided crossings between different Floquet states takes place upon tuning some control parameters. Our studies are predominantly aimed at experimental realizations of ac-driven quantum ratchets with cold atoms.

quant-ph↗

arXiv2006

Optimization of soliton ratchets in inhomogeneous sine-Gordon systems

Unidirectional motion of solitons can take place, although the applied force has zero average in time, when the spatial symmetry is broken by introducing a potential $V(x)$, which consists of periodically repeated cells with each cell containing an asymmetric array of strongly localized inhomogeneities at positions $x_{i}$. A collective coordinate approach shows that the positions, heights and widths of the inhomogeneities (in that order) are the crucial parameters so as to obtain an optimal effective potential $U_{opt}$ that yields a maximal average soliton velocity. $U_{opt}$ essentially exhibits two features: double peaks consisting of a positive and a negative peak, and long flat regions between the double peaks. Such a potential can be obtained by choosing inhomogeneities with opposite signs (e.g., microresistors and microshorts in the case of long Josephson junctions) that are positioned close to each other, while the distance between each peak pair is rather large. These results of the collective variables theory are confirmed by full simulations for the inhomogeneous sine-Gordon system.

cond-mat.mes-hall↗

arXiv2006

Quantum resonances and rectification of driven cold atoms in optical lattices

Classical Hamiltonian ratchets have been recently successfully realized using cold atoms in driven optical lattices. Here we study the current rectification of the motion of a quantum particle in a periodic potential exposed to an external ac field. The dc current appears due to the desymmetrization of Floquet eigenstates, which become transporting. Quantum dynamics enhances the dependence of the current on the initial phase of the driving field. By changing the laser field parameters which control the degree of space-time asymmetry, Floquet eigenstates are tuned through avoided crossings. These quantum resonances induce resonant changes of the resulting current. The width, strength and position of these quantum resonances are tunable using control parameters of the experimental realization with cold atoms.

cond-mat.stat-mech↗