arXane › Physics › Condensed Matter
Wednesday, 4 November 2026: 9 new papers, 2 cross-lists and 4 replacements in Quantum Gases (cond-mat.quant-gas), in arXiv's order, with full abstracts. The same papers as arXiv's own listing, set as a newspaper; every title links to arXiv.
We propose a scheme to realize Weyl superfluidity from topologically trivial bands in the strongly correlated regime of a three-dimensional optical Raman lattice. The scheme builds on a pairing mechanism arising from the interplay between a large Zeeman splitting and strong Hubbard interaction. Spin-flip hopping suppressed by the large Zeeman detuning is resonantly restored when the attractive Hubbard interaction compensates the energy mismatch, yielding a correlated spin-orbit coupling that depends on the local particle configuration. Combining this density-dependent in-plane spin-orbit coupling with density-dependent spin-conserving interlayer tunneling extends the pairing mechanism to three dimensions. A self-consistent mean-field treatment of the microscopic model yields Weyl superfluids with two, four, or eight nodes, together with fully gapped weak topological superfluids. Tuning the interaction strength and particle filling drives transitions between these phases and controls the number of Weyl nodes. We further propose an experimental implementation with ultracold $^{40}\mathrm{K}$ atoms. Our results highlight density-assisted spin-orbit coupling as a mechanism for realizing Weyl superfluidity in strongly correlated systems.
Condensate is an interactive simulator of two-dimensional quantum fluids that runs in a web browser on phones, tablets and computers, with no installation. It solves eight models built on the Gross-Pitaevskii equation: a `vanilla' condensate, a dipolar gas with tilted dipoles, a binary mixture with quantum droplets, Rabi and spin--orbit coupled gases, a self-gravitating (Schr\"odinger-Poisson) condensate, a driven-dissipative polariton fluid, a rotating condensate and a finite-temperature stochastic projected Gross--Pitaevskii equation. A split-step Fourier solver runs on the graphics processor through WebGPU at up to $1024^2$ grid points, with a double-precision CPU engine as a fallback and reference. Users stir the fluid with a laser-like beam, imprint quantised vortices and change parameters while the fluid evolves. Each model comes with a ``Learn'' panel written for graduate students, giving the equations, core physics, and activities that pair an analytic prediction with an experiment in the app, and references keyed to a standard textbook. The whole application is one self-contained HTML file. In this accompanying text, we describe the models, the numerical method and the teaching material.
We study the superfluid phases of a two-dimensional degenerate Fermi gas in an optical lattice subject to a $d_{xy}$-wave altermagnetic term that couples to the in-plane spin component. The single-particle Hamiltonian generates anisotropic Fermi surfaces for the two pseudo-spin species while maintaining zero net polarization. Using the Bogoliubov-de Gennes approach, we show that this anisotropy favors Cooper pairing at a finite center-of-mass momentum, producing a competition between Bardeen-Cooper-Schrieffer (BCS) and Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing and leading to FFLO superfluids. We further examine the effect of a Zeeman-induced spin polarization and find that triplet and singlet pairing channels coexist and compete, resulting in a momentum-selective pairing pattern. Remarkably, this triplet pairing emerges exclusively in the FFLO phase and is entirely absent in the BCS phase. The model is readily realizable in ultracold atoms with current experimental techniques, providing a feasible route for quantum emulation and for studying unconventional superfluid phases.
Magnetic field detection is of great significance in modern fields such as medical diagnostics, geological exploration, inertial navigation, and space physics. We have previously investigated the expansion dynamics of a spin-orbit-coupled Bose-Einstein condensate. Building on these results, here we propose a scheme for magnetic-field-gradient detection by establishing a quantitative relationship between the condensate's rotational deflection angle and the magnetic-field gradient. In this work, we present the parameter dependence of this scheme and perform a systematic optimization. We introduce a Bayesian optimization algorithm to automatically and efficiently search for the optimal combination of key parameters, thereby significantly enhancing the sensitivity of the magnetic field gradient measurement. The results show that the optimized gradiometer improves the sensitivity by a factor of five. This work not only provides a new approach for magnetic field gradient measurement but also serves as a reference for machine learning-empowered quantum precision measurement.
In two dimensions, the kinetic and contact energies scale identically under dilation, a trap $V=r^s/s$ as $\lambda^{-s}$. We follow this balance through the power-law family $-2\le s\le4$, $s\neq0$, for both signs of the coupling $g$, with rotation, using scaling bounds, radial solutions, Bogoliubov spectra, and two-dimensional imaginary-time states. Attraction collapses the cloud at the Townes coupling $g_{*}$ in every trap, with width $\ell\propto\delta^{1/(s+2)}$, $\delta=1-|g|/g_{*}$; repulsion spreads it to a Thomas--Fermi (TF) radius $\propto g^{1/(s+2)}$. A rotating collapse leaves the axis once the rotation frequency $\Omega$ exceeds its dipole frequency, which softens only for $s>2$; in a quartic trap this happens at $\delta\simeq0.32\,\Omega^6$, within $3\%$ of the Bogoliubov threshold; it then collapses on the minimum ring of the rotating-frame potential, which also empties a repulsive TF cloud at $\Omega=(3g/\pi)^{1/6}$. For repulsive vortex states the TF energy error splits exactly into a density-gradient and a flow part of comparable or larger size. At $s=-2$ only the cutoff sets a length: the energy is exactly covariant with it, the condensate falls to the center for both signs, and repulsion leaves a halo of density $\propto1/(gr^2)$ whose extent grows exponentially with $g$. Near collapse, split-step imaginary time has a first-order stationary bias invisible to residual tests.
The cluster Gutzwiller method is widely used to study strongly correlated bosonic systems in optical lattices because it explicitly treats quantum fluctuations within a cluster. However, its computational cost grows exponentially with the cluster size, making large-cluster phase diagrams computationally expensive. To reduce this cost, we recently introduced Delta-learning into cluster Gutzwiller calculations and proposed multipoint regression Delta-learning (MPR-Delta), which learns the difference between small- and large-cluster results from four high-cost critical points of the target cluster and thereby predicts the complete target phase boundary. For sufficiently large target clusters, however, even computing one critical point on the phase boundary is already expensive, so obtaining four such points remains highly costly. A natural question then arises: can the complete target phase boundary be predicted with fewer high-cost critical points of the target cluster? To address this question, we propose single-anchor Delta-learning (SA-Delta), which requires only a single high-cost critical point of the target cluster to reconstruct the complete target phase boundary, thereby greatly reducing the computational cost. We test this framework on several classes of Bose-Hubbard models and find that, in the cases considered, it achieves lower reconstruction errors with fewer high-cost points than MPR-Delta. The combination of SA-Delta with the cluster Gutzwiller approximation thus provides an efficient framework for studying phase transitions of strongly correlated bosonic systems in complex optical lattices, and may be extended to more complex quantum many-body systems.
We investigate the synchronization of coupled photonic Bose-Einstein condensates in dye-filled microcavity arrays, subject to a potential gradient. We show that in the absence of noise the desynchronisation threshold is the result of a dynamical instability. For a two-site system, we analytically derive the maximal potential difference that allows for a synchronized solution as a function of the system parameters and find that it crucially depends on the thermalization rate. For systems with $N$ sites, we find a $N^{-3}$ power law scaling for the critical potential difference. When quantum fluctuations are included, stochastic phase slips broaden the sharp transitions, yet the phase velocity and first order spatial coherence still reliably identify the instability threshold.
Quantized vortices are a hallmark of superfluidity. They have proven to be an indispensable probe for systems ranging from superfluid helium to type-II superconductors. In ultracold two-dimensional (2D) Fermi gases, where phase fluctuations are enhanced and the Berezinskii-Kosterlitz-Thouless (BKT) mechanism governs the superfluid transition, their observation has remained elusive. Here, we report on the controlled creation of quantized vortices in a homogeneous 2D gas in the BEC--BCS crossover. By continuously tuning the velocity of two moving obstacles, we observe quantized steps in the absolute vortex charge. Matter-wave interferometry reveals the characteristic phase winding, quantized in units of $2\pi$. Measurements on 2D and 3D gases show a striking difference: only in 2D does the vortex number grow with temperature, reflecting thermal activation of BKT vortex pairs. Our approach provides evidence of fermionic superfluidity in 2D and offers a means to study BKT physics, vortex-controlled transport and resistance, as well as to detect unconventional superfluidity in spin-imbalanced 2D gases.
Collective flow emerging from spatially anisotropic many-body systems is a fundamental manifestation of strongly interacting quantum matter, from ultracold quantum gases to the quark-gluon plasma created in relativistic heavy-ion collisions. Yet how collective flow emerges across different spatial harmonics and how dissipation modifies its evolution remain largely unexplored. Here we investigate the nonequilibrium expansion of a unitary Fermi gas initially confined in nearly homogeneous potentials with engineered angular deformations. By suddenly releasing the confinement, we resolve anisotropic flow harmonics up to the seventh order. Remarkably, after normalization and rescaling by the characteristic expansion timescale, the different harmonics and system sizes exhibit a universal early-time evolution. At longer times, this universality breaks down and we observe an approximately quadratic dependence of the harmonic attenuation on harmonic order, consistent with viscous acoustic scaling. Furthermore, temperature-dependent measurements reveal the role of shear viscosity in the dissipative evolution of higher-order flow. Our results open a new route to exploring the interplay between universal hydrodynamic expansion and dissipative transport, connecting collective dynamics in ultracold quantum gases with anisotropic flow in strongly interacting nuclear matter.
Atomic arrays provide a cooperative platform for light-mediated interactions in nonlocal metasurfaces which can operate in the quantum regime without nanofabricated optical elements or intrinsic material absorption. We present a minimal atomic implementation to harness wavefront engineering and create a near-ideal intrinsic atomic Huygens' surface. A simple bilayer square lattice with a two-atom unit cell, not limited to small lattice spacings, provides near-unity reflectionless transmission and a full $2\pi$ phase control of transmitted light without the localized site-dependent level shifts of previous proposals. This simplification is achieved through nonlocal radiative excitations that provide the familiar electric-dipole response with even radiation parity as well as an odd-parity radiation channel whose leading multipolar interpretation combines magnetic-dipole and electric-quadrupole contributions in atoms exhibiting only electric dipole transitions. This eliminates the need to simultaneously excite pure electric-dipole and magnetic-dipole responses with exactly matched radiation. We derive a two-mode model for this response and show that it accurately captures full coupled-dipole simulations near the optimal lattice spacings. Because of the wide applicability of coupled-dipole models, the relevance of our microscopic analysis extends beyond atomic physics to nanostructured metasurfaces. Moreover, the same platform also connects directly to established subradiance-protected single-photon storage protocols, suggesting a route toward combining wavefront engineering, storage, and retrieval in a simple atomic bilayer.
Ultracold polar molecules present a rich platform for experimental quantum science leveraging their unique properties. Of particular relevance is the intrinsic electric dipole moment of the molecule, which results in strong coupling to microwave fields and can be used to engineer long-range, anisotropic, and tunable dipole-dipole interactions. Such interactions can generate entanglement between molecules and enable the study of novel quantum many-body phenomena in parameter regimes inaccessible in other systems. Modern experiments in optical tweezers and optical lattices have demonstrated controlled interactions between molecules in coherent quantum states, and recently bulk gases of molecules have been cooled to quantum degeneracy. Motivated by these landmark advances, we present this article to explain many of the key concepts relevant to current research in the field.