arXiv subjects

Thomas Bland

Publications and source records attributed to Thomas Bland.

At least 19 recordsLinked to original sources

arXiv2026

Soliton-to-droplet crossover in a dipolar Bose gas in one and two dimensions

We analyze a system of dipolar atoms confined in geometries of quasi-low-dimensionality. Due to the long-range and anisotropic nature of dipolar interactions, the system supports both stable solitons and quantum droplets. In quasi-one-dimensional geometries, the transition between these states is known to manifest either as a first-order phase transition, associated with bistability, or as a smooth crossover. We investigate this transition by calculating the structure factor and showing that the response of the breathing mode provides an experimentally accessible probe. In addition, we identify regions of both bistability and smooth crossover in quasi-two-dimensional geometries. Finally, we connect our findings to previous experimental results and delineate the conditions under which two-dimensional dipolar bright solitons can be realized.

cond-mat.quant-gas↗

arXiv2025

Exploring molecular supersolidity via exact and mean-field theories: single microwave shielding

Ultracold polar molecules with microwave shielding provide a powerful platform for exploring quantum many-body physics with strong, anisotropic interactions. We develop an extended Gross-Pitaevskii framework for bosonic molecules under single microwave shielding, incorporating effective interactions and quantum fluctuations, and benchmark it against exact Quantum Monte Carlo simulations. In the regime of positive scattering lengths, our approach captures superfluid, supersolid, and droplet phases with excellent accuracy. We show that elliptic microwave polarization induces direction-dependent superfluidity--absent in cylindrically symmetric systems. A quasi-1D theory reveals that roton softening and instabilities can be controlled via ellipticity, consistent with recent experiments. Furthermore, we find that the nature of the superfluid-to-supersolid transition is strongly influenced by the ellipticity: the transition is sharp at low ellipticity and continuous at higher values. This tunability offers a potential route for low entropy preparation of molecular supersolids via adiabatic ramps. While double shielding is often used experimentally, our results demonstrate that single-shielded molecules already offer rich, controllable behavior, laying the groundwork for future studies with more complex shielding schemes.

cond-mat.quant-gas↗

arXiv2025

Topology meets superconductivity in a one-dimensional $t-J$ model of magnetic atoms

Strongly interacting fermions represent the key constituent of several intriguing phases of matter. However, due to the inherent complexity of these systems, important regimes are still inaccessible. Here, we derive a realistic and flexible setup based on ultracold magnetic lanthanide atoms trapped in a one-dimensional optical lattice. Leveraging their large magnetic moments, we design a fermionic $t-J$ model with independently tunable hopping, spin-spin couplings, and onsite interaction. Through combined analytical and numerical analysis, we uncover a variety of many-body quantum phases$-$including superconducting and topological states. Crucially, in the regime of attractive onsite interaction we reveal that topology and superconductivity coexist, thus giving rise to an exotic state of matter: a topological triplet superconductor. We also outline a practical protocol to prepare and detect all discovered phases using current experimental techniques. Our results establish an alternative and powerful route for a deeper understanding of strongly interacting fermionic quantum matter.

cond-mat.quant-gas↗

arXiv2025

Analytic Phase Solution and Point Vortex Model for Dipolar Quantum Vortices

We derive an analytic expression for the phase of a quantum vortex in a dipolar Bose-Einstein condensate, capturing anisotropic effects from long-range dipole-dipole interactions. This solution provides a foundation for a dipolar point vortex model (DPVM), incorporating both phase-driven flow and dipolar forces. The DPVM reproduces key features of vortex pair dynamics seen in full simulations, including anisotropic velocities, deformed orbits, and directional motion, offering a minimal and accurate model for dipolar vortex dynamics. Our results open the door to analytic studies of vortices in dipolar quantum matter and establish a new platform for exploring vortex dynamics and turbulence in these systems.

cond-mat.quant-gas↗

arXiv2025

Quantum Carpets of Higgs particles in a Supersolid

Supersolids formed from dipolar Bose-Einstein condensates (BECs) exhibit spontaneous density modulation while maintaining global phase coherence. This state of matter supports gapped amplitude (Higgs) excitations featuring a quadratic dispersion relation. While Higgs modes are typically strongly damped due to coupling with other amplitude and phase modes, imposing an experimentally realistic toroidal geometry allows us to numerically study the time evolution and dispersion of a localized Higgs quasiparticle excitation, with minimal residual coupling to sound modes. Strikingly, the quadratic dispersion leads to the occurrence of (fractional) revivals, similar to those seen in the optical Talbot effect or the so-called quantum carpets. The revival times provide a novel method for determining the effective mass of the Higgs particle through a non-spectroscopic approach. These results pave the way for further studies of coherent Higgs dynamics and mutual interactions between Higgs particles.

cond-mat.quant-gas↗

arXiv2024

Synchronization in rotating supersolids

Synchronization is ubiquitous in nature at various scales and fields. This phenomenon not only offers a window into the intrinsic harmony of complex systems, but also serves as a robust probe for many-body quantum systems. One such system is a supersolid: an exotic state that is simultaneously superfluid and solid. Here, we show that putting a supersolid under rotation leads to a synchronization of the crystal's motion to an external driving frequency triggered by quantum vortex nucleation, revealing the system's dual solid-superfluid response. Benchmarking the theoretical framework against experimental observations, we exploit this model as a novel method to investigate the critical frequency required for vortex nucleation. Our results underscore the utility of synchronization as a powerful probe for quantum systems.

cond-mat.quant-gas↗

arXiv2024

Anomalous dispersion of shear waves in dipolar supersolids

Dipolar supersolids--quantum states that are simultaneously superfluid and solid--have had their superfluid nature rigorously tested, while their solid nature remain uncharted. Arguably, the defining characteristic of a solid is the existence of elastic shear waves. In this work we investigate transverse wave packet propagation in dipolar supersolids with triangular and honeycomb structure. Remarkably, the honeycomb supersolid displays anomalous dispersion, supporting waves traveling faster than the transverse speed of sound. While the distinction between anomalous and normal dispersion appears subtle, it has a profound influence on both the transport and scattering properties. For both supersolid phases, we calculate the shear modulus, a key parameter that quantifies the material's rigidity. Our findings are pertinent to current experimental efforts scrutinizing the fundamental properties of supersolids.

cond-mat.quant-gas↗

arXiv2024

Exploring pulsar glitches with dipolar supersolids

Glitches are sudden spin-up events that interrupt the gradual spin-down of rotating neutron stars. They are believed to arise from the rapid unpinning of vortices in the neutron star inner crust. The analogy between the inner crust of neutron stars and dipolar supersolids allows to investigate glitches. Employing such analogy, we numerically analyze the vortex trapping mechanism and how the matter density distribution influences glitches. These results pave the way for the quantum simulation of celestial bodies in laboratories.

cond-mat.quant-gas↗

arXiv2024

Observation of vortices in a dipolar supersolid

Supersolids are states of matter that spontaneously break two continuous symmetries: translational invariance due to the appearance of a crystal structure and phase invariance due to phase locking of single-particle wave functions, responsible for superfluid phenomena. While originally predicted to be present in solid helium, ultracold quantum gases provided a first platform to observe supersolids, with particular success coming from dipolar atoms. Phase locking in dipolar supersolids has been probed through e.g. measurements of the phase coherence and gapless Goldstone modes, but quantized vortices, a hydrodynamic fingerprint of superfluidity, have not yet been observed. Here, with the prerequisite pieces at our disposal, namely a method to generate vortices in dipolar gases and supersolids with two-dimensional crystalline order, we report on the theoretical investigation and experimental observation of vortices in the supersolid phase. Our work reveals a fundamental difference in vortex seeding dynamics between unmodulated and modulated quantum fluids. This opens the door to study the hydrodynamic properties of exotic quantum systems with multiple spontaneously broken symmetries, in disparate domains such as quantum crystals and neutron stars.

cond-mat.quant-gas↗

arXiv2023

Vortices in dipolar Bose-Einstein condensates

Quantized vortices are the hallmark of superfluidity, and are often sought out as the first observable feature in new superfluid systems. Following the recent experimental observation of vortices in Bose-Einstein condensates comprised of atoms with inherent long-range dipole-dipole interactions [Nat. Phys. 18, 1453-1458 (2022)], we thoroughly investigate vortex properties in the three-dimensional dominantly dipolar regime, where beyond-mean-field effects are crucial for stability, and investigate the interplay between trap geometry and magnetic field tilt angle.

cond-mat.quant-gas↗

arXiv2023

Glitches in rotating supersolids

Glitches, spin-up events in neutron stars, are of prime interest as they reveal properties of nuclear matter at subnuclear densities. We numerically investigate the glitch mechanism due to vortex unpinning using analogies between neutron stars and dipolar supersolids. We explore the vortex and crystal dynamics during a glitch and its dependence on the supersolid quality, providing a tool to study glitches from different radial depths of a neutron star. Benchmarking our theory against neutron star observations, our work will open a new avenue for the quantum simulation of stellar objects from Earth.

cond-mat.quant-gas↗

arXiv2022

Alternating-domain supersolids in binary dipolar condensates

Two-component dipolar condensates are now experimentally producible, and we theoretically investigate the nature of supersolidity in this system. We predict the existence of a binary supersolid state in which the two components form a series of alternating domains, producing an immiscible double supersolid. Remarkably, we find that a dipolar component can even induce supersolidity in a nondipolar component. In stark contrast to single-component dipolar supersolids, alternating-domain supersolids do not require quantum stabilization, and the number of crystal sites is not strictly limited by the condensate populations, with the density hence being substantially lower. Our results are applicable to a wide range of dipole moment combinations, marking an important step towards long-lived bulk-supersolidity.

cond-mat.quant-gas↗

arXiv2022

Observation of vortices and vortex stripes in a dipolar Bose-Einstein condensate

Quantized vortices are the prototypical feature of superfluidity. Pervasive in all natural systems, vortices are yet to be observed in dipolar quantum gases. Here, we exploit the anisotropic nature of the dipole-dipole interaction of a dysprosium Bose-Einstein condensate to induce angular symmetry breaking in an otherwise cylindrically symmetric pancake-shaped trap. Tilting the magnetic field towards the radial plane deforms the cloud into an ellipsoid through magnetostriction, which is then set into rotation. At stirring frequencies approaching the radial trap frequency, we observe the generation of dynamically unstable surface excitations, which cause angular momentum to be pumped into the system through vortices. Under continuous rotation, the vortices arrange into a stripe configuration along the field--in close corroboration with simulations--realizing a long sought-after prediction for dipolar vortices.

cond-mat.quant-gas↗

arXiv2022

Two-Dimensional Supersolid Formation in Dipolar Condensates

Dipolar condensates have recently been coaxed to form the long-sought supersolid phase. While one-dimensional supersolids may be prepared by triggering a roton instability, we find that such a procedure in two dimensions (2D) leads to a loss of both global phase coherence and crystalline order. Unlike in 1D, the 2D roton modes have little in common with the supersolid configuration. We develop a finite-temperature stochastic Gross-Pitaevskii theory that includes beyond-mean-field effects to explore the formation process in 2D and find that evaporative cooling directly into the supersolid phase--hence bypassing the first-order roton instability--can produce a robust supersolid in a circular trap. Importantly, the resulting supersolid is stable at the final nonzero temperature. We then experimentally produce a 2D supersolid in a near-circular trap through such an evaporative procedure. Our work provides insight into the process of supersolid formation in 2D and defines a realistic path to the formation of large two-dimensional supersolid arrays.

cond-mat.quant-gas↗

arXiv2021

Maintaining supersolidity in one and two dimensions

We theoretically investigate supersolidity in three-dimensional dipolar Bose-Einstein condensates. We focus on the role of trap geometry in determining the dimensionality of the resulting droplet arrays, which range from one-dimensional to zigzag, through to two-dimensional supersolids in circular traps. Supersolidity is well established in one-dimensional arrays, and may be just as favorable in two-dimensional arrays provided that one appropriately scales the atom number to the trap volume. We develop a tractable variational model--which we benchmark against full numerical simulations--and use it to study droplet crystals and their excitations. We also outline how exotic ring and stripe states may be created with experimentally-feasible parameters. Our work paves the way for future studies of two-dimensional dipolar supersolids in realistic settings.

cond-mat.quant-gas↗

arXiv2021

Can angular oscillations probe superfluidity in dipolar supersolids?

Angular oscillations can provide a useful probe of the superfluid properties of a system. Such measurements have recently been applied to dipolar supersolids, which exhibit both density modulation and phase coherence, and for which robust probes of superfluidity are particularly interesting. So far, these investigations have been confined to linear droplet arrays. Here, we explore angular oscillations in systems with 2D structure, which in principle have greater sensitivity to superfluidity. Surprisingly, in both experiment and simulation, we find that the frequency of angular oscillations remains nearly unchanged even when the superfluidity of the system is altered dramatically. This indicates that angular oscillation measurements do not always provide a robust experimental probe of superfluidity with typical experimental protocols.

cond-mat.quant-gas↗

arXiv2020

Quantum droplets of quasi-one-dimensional dipolar Bose-Einstein condensates

Ultracold dipolar droplets have been realized in a series of ground-breaking experiments, where the stability of the droplet state is attributed to beyond-mean-field effects in the form of the celebrated Lee-Huang-Yang (LHY) correction. We scrutinize the dipolar droplet states in a one-dimensional context using a combination of analytical and numerical approaches, and identify experimentally viable parameters for accessing our findings for future experiments. In particular we identify regimes of stability in the restricted geometry, finding multiple roton instabilities as well as regions supporting quasi-one-dimensional droplet states. By applying an interaction quench to the droplet, a modulational instability is induced and multiple droplets are produced, along with bright solitons and atomic radiation. We also assess the droplets robustness to collisions, revealing population transfer and droplet fission.

cond-mat.quant-gas↗

arXiv2020

Periodic quenches across the Berezinskii-Kosterlitz-Thouless phase transition

The quenched dynamics of an ultracold homogeneous atomic two-dimensional Bose gas subjected to periodic quenches across the Berezinskii-Kosterlitz-Thouless (BKT) phase transition are discussed. Specifically, we address the effect of periodic cycling of the effective atomic interaction strength between a thermal disordered state above, and a highly ordered state below the critical BKT interaction strength, by means of numerical simulations of the stochastic projected Gross-Pitaevskii equation. Probing the emerging dynamics as a function of the frequency of sinusoidal driving from low to high frequencies reveals diverse dynamical features, including phase-lagged quasi adiabatic reversible condensate formation, resonant excitation consistent with an intrinsic system relaxation timescale, and gradual establishment of dynamically-recurring or time-averaged non-equilibrium states with enhanced coherence which are neither condensed, nor thermal. Our study paves the way for experimental observation of such driven non-equilibrium ultracold superfluid states.

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