arXiv subjects

Aitor Alaña

Publications and source records attributed to Aitor Alaña.

7 recordsLinked to original sources

arXiv2026

Smooth time-dependent control of dipolar Bose-Einstein condensates

We consider protocols for control of dipolar Bose-Einstein condensates where the critical role is played by the long-range anisotropic interatomic magnetic dipole-dipole interaction. The phase diagram of such a condensate has been explored theoretically and experimentally with certain values of the interatomic scattering length corresponding to superfluid and supersolid phases, where supersolidity appears as a modulation in the ground state density. Preparation of this modulated ground state is challenging, since excitations appear as a result of a finite-time evolution required to produce qualitative changes in the wavefunction density. To solve this problem we consider the time-dependent control of a dipolar Bose-Einstein condensate using shortcuts to adiabaticity techniques, concentrating on design of the time-dependent scattering length, a parameter of the system easily tunable by contemporary experiments. The first technique is the variational approach based on the Euler-Lagrange equations for a separable ansatz describing the evolution of the superfluid state. Secondly, we study the transition from superfluid to supersolid using a direct optimization protocol. We discuss the fidelity of the developed protocols in terms of the evolution time.

cond-mat.quant-gas↗

arXiv2026

Vortex dynamics in rotating dipolar supersolids across Josephson and self-trapping regimes

We investigate vortex nucleation and transport in a rotating dipolar supersolid arranged in a triangular droplet lattice, exploiting its description as an array of weakly linked condensates. By considering both Josephson and macroscopic self-trapping dynamics, we show that local phase differences between droplets provide a compact and highly predictive framework to explore a wide range of vortex behaviors. In particular, Josephson oscillations can be devised to induce vortex nucleation and motion near the vertices of the low-density hexagonal lattice (between droplets), while self-trapping dynamics induce running phases that enable directed vortex transport, which may be accompanied by vortex-antivortex pair creation and annihilation over finite time scales. Comparison with simulations based on the extended Gross-Pitaevskii equation demonstrates that a three-droplet description is essential to capture vortex motion near hexagon vertices. Together, Josephson and self-trapping dynamics provide a tunable protocol to trigger and track vortex nucleation, transport, and vortex-antivortex pair annihilation, revealing the microscopic topological mechanisms underlying phase slips in rotating dipolar supersolids.

cond-mat.quant-gas↗

arXiv2025

Self-sustained Josephson dynamics and self-trapping in supersolids

We explore the self-sustained Josephson junction dynamics in dipolar supersolids, predicting the possibility of self-trapping alongside the experimentally observed Josephson oscillations [Biagioni, G. et al., Nature 629, 773 (2024)]. Using an asymmetric two-mode (ATM) model to describe a triangular dipolar supersolid, validated through Gross-Pitaevskii simulations, we demonstrate that the system's symmetry enables a consistent two-mode mapping despite the presence of seven droplets. Hence, the associated Hamiltonian allows us to straightforwardly determine the self-trapping regime. Additionally, we show that bringing the system into rotation preserves its ability to sustain the Josephson junction dynamics across its full range, and we assess the robustness of the ATM model under these conditions. We further find that the off-axis droplets move in the radial direction during the evolution in accordance with the size of the central droplet. Such movements do not interfere with the model predictions.

cond-mat.quant-gas↗

arXiv2024

Phase-induced vortex pinning in rotating supersolid dipolar systems

We analyze the pinning of vortices for a stationary rotating dipolar supersolid along the low-density paths between droplets as a function of the rotation frequency. We restrict ourselves to the stationary configurations of vortices with the same symmetry as that of the array of droplets. In particular, such an analysis clearly reveals that vortices are not only pinned at local density minima, but instead their coordinates are smooth functions of the rotation frequency. Our approach to explaining such a behavior exploits the fact that the wave function of each rotating droplet acquires a linear phase on the coordinates. Hence, the relative phases between the nearest neighboring droplets allow us to predict the position of the vortices in the intermediate low-density region. Here, we show that for a droplet distribution forming a triangular lattice, the phases of three neighboring droplets are needed for the correct description of the vortex location. In particular, for our confined system, we demonstrate that the estimate accurately reproduces the extended Gross-Pitaevskii results in the spatial regions where the neighboring droplets are well-defined.

cond-mat.quant-gas↗

arXiv2024

Supersolid formation time shortcut and excitation reduction by manipulating the dynamical instability

Supersolids are a phase of matter exhibiting both superfluidity and a periodic density modulation typical of crystals. When formed via quantum phase transition from a superfluid, they require a formation time before their density pattern develops. Along this paper some protocols/schemes are proposed for experimental applications, building on earlier descriptions of the role roton instability plays in the supersolid formation process and the associated formation time. In particular, the Parachutejump scheme sought to lessen the excitation produced when crossing the phase transition, and the Bang-Bang method sought to shorten the formation time. As a case study of the impact that mechanical fluctuations (noise) can have on the phase transition when conducting an experiment, the impact of a mechanical kick before the transition is also investigated. The proposed schemes are able to fulfill their objectives successfully as both the shortening of the formation process and the reduction of excitation are achieved within the framework of extended Gross Pitaevskii theory.

cond-mat.quant-gas↗

arXiv2023

Supersolid formation in a dipolar condensate by roton instability

We characterize the role of the roton instability in the formation of a supersolid state of an elongated dipolar condensate, following a quench of the contact interactions across the superfluid-supersolid transition, as observed in recent experiments. We perform dynamical simulations by means of the extended Gross-Pitaevskii equation including quantum corrections, for different final values of the $s-$wave scattering length. The corresponding excitation spectrum is computed using an effective one-dimensional description, revealing that the calculated growth rates of the unstable roton mode accurately reproduce the observed behavior. Our results provide valuable insights regarding the formation time of the supersolid and its scaling behavior with respect to the $s$-wave scattering length.

cond-mat.quant-gas↗

arXiv2022

Crossing the superfluid-supersolid transition of an elongated dipolar condensate

We provide a theoretical characterization of the dynamical crossing of the superfluid-supersolid phase transition for a dipolar condensate confined in an elongated trap, as observed in the recent experiment by G. Biagioni et al. [Phys. Rev. X 12, 021019 (2022)]. By means of the extended Gross-Pitaevskii theory, which includes the Lee-Huang-Yang quantum fluctuation correction, we first analyze the ground state configurations of the system as a function of the interparticle scattering length, for both trap configurations employed in the experiment. Then, we discuss the effects of the ramp velocity, by which the scattering length is tuned across the transition, on the collective excitations of the system in both the superfluid and supersolid phases. We find that, when the transverse confinement is sufficiently strong and the transition has a smooth (continuous) character, the system essentially displays a (quasi) 1D behavior, its excitation dynamics being dominated by the axial breathing modes. Instead, for shallower transverse trapping, when the transition becomes discontinuous, the collective excitations of the supersolid display a coupling with the transverse modes, signalling the onset of a dimensional crossover.

cond-mat.quant-gas↗