arXiv subjects

L. Santos

Publications and source records attributed to L. Santos.

At least 19 recordsLinked to original sources

arXiv2026

The science of compressional heating on the LM26 magnetized target fusion experiment

The Lawson Machine 26 (LM26) at General Fusion has demonstrated compressional heating of a spherical tokamak deuterium plasma as it was compressed by an imploding solid lithium liner. Results from the first 11 compression shots on LM26 are presented, the highest-performing of which show more than a 3x increase in $T_e$, a 10x increase in $n_e$, and a 10x increase in $B_{pol}$ within the plasma driven by 3x radial compression. The experimental device and instrumentation are reviewed in detail, followed by observations about the liner trajectory and evolution of plasma properties, including increases in emission of neutrons, X-rays, and visible radiation. Observations from fast-camera images during compression provide context for interpreting the spatial structure of plasma-wall interaction. Overviews of relevant models and analysis are presented. Diagnostic data are used to reconstruct the experimental equilibrium state in computational framework as a function of time. The results build confidence in the stability and transport analyses that support the primary conclusions. Trends across the full set of 11 compression shots are presented, and detailed examinations of the high-performance shots are given individually. The central conclusions of the integrated physics model specifically indicate that compressional heating was achieved in this set of experiments, as evidenced by the balance of heating power from compression, Ohmic heating from plasma current, and losses to the boundary needed to match the experimental data. A majority of the temperature rise is attributable to compressional heating. An increase in neutron flux is also observed during compression. The results provide a basis for planned improvements to the LM26 facility that will enable the compression of magnetized plasma to increasingly higher densities and temperatures.

physics.plasm-ph↗

arXiv2024

Polarons and bipolarons in Rydberg-dressed extended Bose-Hubbard model

Impurities immersed in hard-core Bose gases offer exciting opportunities to explore polaron and bipolaron physics. We investigate the ground state properties of a single and a pair of impurities throughout the superfluid and insulating (charge density wave) phases of the bosonic environment. In the superfluid phase, the impurity exhibits polaron-like behavior, forming a dressed quasiparticle. In contrast, in the insulating phase, the impurity regains its particle-like character, moving through a potential landscape shaped by the charge density wave order. Moreover, we show that two impurities can form a bound state even in the absence of an explicit impurity-impurity coupling. We establish the stability of this bound state within both the superfluid and insulating phases. Our results offer valuable insights for ongoing lattice polaron experiments with ultracold gases.

cond-mat.quant-gas↗

arXiv2024

Non-Abelian vibron dynamics in trapped-ion arrays

Trapped-ion arrays offer interesting possibilities for quantum simulation. We show that a proper arrangement of elliptical micro-traps combined with the external driving of the micro-trap frequencies allows, without the need of any precise fine-tuning, for the robust realization of non-Abelian vibron dynamics. We show that this non-Abelian nature may be readily probed experimentally in a simple plaquette arrangement. This study opens interesting perspectives for the study of non-Abelian spin-orbit coupling with motional excitations in two- and three-dimensional ion arrays.

physics.atom-ph↗

arXiv2023

Lattice control of non-ergodicity in a polar lattice gas

Inter-site interactions in polar lattice gases may result, due to Hilbert-space fragmentation, in a lack of ergodicity even in absence of disorder. We show that the inter-site interaction in a one-dimensional dipolar gas in an optical lattice departs from the usually considered $1/r^3$ dependence, acquiring a universal form that depends on the transversal confinement and the lattice depth. Due to the crucial role played by the nearest- and next-to-nearest neighbors, the Hilbert-space fragmentation and particle dynamics are very similar to that of a power-law model $1/r^{β_{\mathrm{eff}}<3}$, where $β_{\mathrm{eff}}$ is experimentally controllable by properly tailoring the transversal confinement. Our results are of direct experimental relevance for experiments on dipolar gases in optical lattices, and show that the particle dynamics may be remarkably different if the quasi-1D lattice model is realized in a strong 3D lattice, or by means of a strong transversal harmonic confinement.

cond-mat.quant-gas↗

arXiv2023

Impurities in quasi-one-dimensional droplets of binary Bose mixtures

Recently created self-bound quantum droplets of binary Bose mixtures open intriguing possibilities for the study of impurity physics. We show that the properties of impurities embedded in quasi-one-dimensional droplets are determined by the interplay between back-action and quantum fluctuations. Due to such back-action, repulsive impurities may form a metastable quasi-bound state inside the droplet. In contrast, attractive impurities remain bound to the droplet, leading to the hybridization of droplet and impurity excitations, as well as to peculiar scattering resonances. Interestingly, impurity trapping may result solely from the effect of quantum fluctuations. These results may readily be probed experimentally by doping the currently available droplets of binary mixtures.

cond-mat.quant-gas↗

arXiv2023

Transversal effects on the ground-state of hard-core dipolar bosons in one-dimensional optical lattices

Polar lattice gases are usually assumed to have an inter-site interaction that decays with the inter-particle distance $r$ as $1/r^3$. However, a loose-enough transversal confinement may strongly modify the dipolar decay in one-dimensional lattices. We show that this modification alters significantly the ground-state properties of hard-core dipolar bosons. For repulsive inter-site interactions, the corrected decay alters the conditions for devil's staircase insulators, affecting significantly the particle distribution in the presence of an overall harmonic confinement. For attractive interactions, it results in a reduction of the critical dipole interaction for the formation of self-bound clusters, and for a marked enhancement of the region of liquefied lattice droplets.

cond-mat.quant-gas↗

arXiv2023

Heat transport in a Coulomb ion crystal with a topological defect

The thermodynamics of low-dimensional systems departs significantly from phenomenologically deducted macroscopic laws. Particular examples, not yet fully understood, are provided by the breakdown of Fourier's law and the ballistic transport of heat. Low-dimensional trapped ion systems provide an experimentally accessible and well-controlled platform for the study of these problems. In our work, we study the transport of thermal energy in low-dimensional trapped ion crystals, focusing in particular on the influence of the Aubry-like transition that occurs when a topological defect is present in the crystal. We show that the transition significantly hinders efficient heat transport, being responsible for the rise of a marked temperature gradient in the non-equilibrium steady state. Further analysis reveals the importance of the motional eigenfrequencies of the crystal.

physics.atom-ph↗

arXiv2023

Catalyzation of supersolidity in binary dipolar condensates

Breakthrough experiments have newly explored the fascinating physics of dipolar quantum droplets and supersolids. The recent realization of dipolar mixtures opens further intriguing possibilities. We show that under rather general conditions, the presence of a second component catalyzes droplet nucleation and supersolidity in an otherwise unmodulated condensate. Droplet catalyzation in miscible mixtures, which may occur even for a surprisingly small impurity doping, results from a local roton instability triggered by the doping-dependent modification of the effective dipolar strength. The catalyzation mechanism may trigger the formation of a two-fluid supersolid, characterized by a generally different superfluid fraction of each component, which opens intriguing possibilities for the future study of spin physics in dipolar supersolids.

cond-mat.quant-gas↗

arXiv2022

On a class of nonlocal problems with fractional gradient constraint

We consider a Hilbertian and a charges approach to fractional gradient constraint problems of the type $|D^σu|\leq g$, involving the distributional fractional Riesz gradient $D^σ$, $0<σ<1$, extending previous results on the existence of solutions and Lagrange multipliers of these nonlocal problems. We also prove their convergence as $σ\nearrow1$ towards their local counterparts with the gradient constraint $|D u|\leq g$.

math.AP↗

arXiv2021

Quantum nanofriction in trapped ion chains with a topological defect

Trapped ion systems constitute a well controllable scenario for the study and emulation of nanofriction, and in particular of Frenkel-Kontorova-like models. This is in particular the case when a topological defect is created in a zigzag ion Coulomb crystal, which results in an Aubry transition from free sliding to pinned phase as a function of the trap aspect ratio. We explore the quantum effects of the Aubry transition by means of an effective simplified model, in which the defect is treated like a single quantum particle that experiences an effective Peierls-Nabarro potential and a position-dependent mass. We demonstrate the relevance of quantum tunneling in a finite range of aspect ratios close the critical point, showing that the quantum effects may be observed in the kink dynamics for sufficiently low temperatures. Finally, we discuss the requirements to reveal quantum effects at the Aubry transition in future experiments on trapped ions.

cond-mat.quant-gas↗

arXiv2021

Quantum droplets of dipolar mixtures

Recently achieved two-component dipolar Bose-Einstein condensates open exciting possibilities for the study of mixtures of ultra-dilute quantum liquids. While non-dipolar self-bound mixtures are necessarily miscible with an approximately fixed ratio between the two densities, the density ratio for the dipolar case is free. As a result, self-bound dipolar mixtures present qualitatively novel and much richer physics, characterized by three possible ground-state phases: miscible, symmetric immiscible and asymmetric immiscible, which may in principle occur at any population imbalance. Self-bound immiscible droplets are possible due to mutual non-local inter-component attraction, which results in the formation of a droplet molecule. Moreover, our analysis of the impurity regime, shows that quantum fluctuations in the majority component crucially modify the miscibility of impurities. Our work opens intriguing perspectives for the exploration of spinor physics in ultra-dilute liquids, which should resemble to some extent that of 4He-3He droplets and impurity-doped helium droplets.

cond-mat.quant-gas↗

arXiv2020

Momentum Entanglement for Atom Interferometry

Compared to light interferometers, the flux in cold-atom interferometers is low and the associated shot noise large. Sensitivities beyond these limitations require the preparation of entangled atoms in different momentum modes. Here, we demonstrate a source of entangled atoms that is compatible with state-of-the-art interferometers. Entanglement is transferred from the spin degree of freedom of a Bose-Einstein condensate to well-separated momentum modes, witnessed by a squeezing parameter of -3.1(8) dB. Entanglement-enhanced atom interferometers open up unprecedented sensitivities for quantum gradiometers or gravitational wave detectors.

quant-ph↗

arXiv2019

Energy localization in interacting atomic chains with topological solitons

Topological defects in low-dimensional non-linear systems feature a sliding-to-pinning transition of relevance for a variety of research fields, ranging from biophysics to nano- and solid-state physics. We find that the dynamics after a local excitation results in a highly-non-trivial energy transport in the presence of a topological soliton, characterized by a strongly enhanced energy localization in the pinning regime. Moreover, we show that the energy flux in ion crystals with a topological defect can be sensitively regulated by experimentally accessible environmental parameters. Whereas, third-order non-linear resonances can cause an enhanced long-time energy delocalization, robust energy localization persists for distinct parameter ranges even for long evolution times and large local excitations.

quant-ph↗

arXiv2019

One-dimensional quasicrystals with power-law hopping

One-dimensional quasi-periodic systems with power-law hopping, $1/r^a$, differ from both the standard Aubry-Azbel-Harper (AAH) model and from power-law systems with uncorrelated disorder. Whereas in the AAH model all single-particle states undergo a transition from ergodic to localized at a critical quasi-disorder strength, short-range power-law hops with $a>1$ can result in mobility edges. Interestingly, there is no localization for long-range hops with $a\leq 1$, in contrast to the case of uncorrelated disorder. Systems with long-range hops are rather characterized by ergodic-to-multifractal edges and a phase transition from ergodic to multifractal (extended but non ergodic) states. We show that both mobility and ergodic-to-multifractal edges may be clearly revealed in experiments on expansion dynamics.

cond-mat.dis-nn↗

arXiv2019

Disorderless quasi-localization of polar gases in one-dimensional lattices

One-dimensional polar gases in deep optical lattices present a severely constrained dynamics due to the interplay between dipolar interactions, energy conservation, and finite bandwidth. The appearance of dynamically-bound nearest-neighbor dimers enhances the role of the $1/r^3$ dipolar tail, resulting, in the absence of external disorder, in quasi-localization via dimer clustering for very low densities and moderate dipole strengths. Furthermore, even weak dipoles allow for the formation of self-bound superfluid lattice droplets with a finite doping of mobile, but confined, holons. Our results, which can be extrapolated to other power-law interactions, are directly relevant for current and future lattice experiments with magnetic atoms and polar molecules.

cond-mat.quant-gas↗

arXiv2018

Creation of entangled atomic states by an analogue of the Dynamical Casimir Effect

If the boundary conditions of the quantum vacuum are changed in time, quantum field theory predicts that real, observable particles can be created in the initially empty modes. Here, we realize this effect by changing the boundary conditions of a spinor Bose-Einstein condensate, which yields a population of initially unoccupied spatial and spin excitations. We prove that the excitations are created as entangled excitation pairs by certifying continuous-variable entanglement within the many-particle output state.

quant-ph↗

arXiv2018

Quenched dynamics and spin-charge separation in an interacting topological lattice

We analyze the static and dynamical properties of a one-dimensional topological lattice, the fermionic Su-Schrieffer-Heeger model, in the presence of on-site interactions. Based on a study of charge and spin correlation functions, we elucidate the nature of the topological edge modes, which depending on the sign of the interactions, either display particles of opposite spin on opposite edges, or a pair and a holon. This study of correlation functions also highlights the strong entanglement that exists between the opposite edges of the system. This last feature has remarkable consequences upon subjecting the system to a quench, where an instantaneous edge-to-edge signal appears in the correlation functions characterizing the edge modes. Besides, other correlation functions are shown to propagate in the bulk according to the light-cone imposed by the Lieb-Robinson bound. Our study reveals how one-dimensional lattices exhibiting entangled topological edge modes allow for a non-trivial correlation spreading, while providing an accessible platform to detect spin-charge separation using state-of-the-art experimental techniques.

cond-mat.quant-gas↗

arXiv2018

Duality in power-law localization in disordered one-dimensional systems

The transport of excitations between pinned particles in many physical systems may be mapped to single-particle models with power-law hopping, $1/r^a$. For randomly spaced particles, these models present an effective peculiar disorder that leads to surprising localization properties. We show that in one-dimensional systems almost all eigenstates (except for a few states close to the ground state) are power-law localized for any value of $a>0$. Moreover, we show that our model is an example of a new universality class of models with power-law hopping, characterized by a duality between systems with long-range hops ($a<1$) and short-range hops ($a>1$) in which the wave function amplitude falls off algebraically with the same power $γ$ from the localization center.

cond-mat.dis-nn↗