Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Condensed Matter Quantum Gases

cond-mat.quant-gas Watch Quantum Gases

Wednesday 26 August

Quantum Gases

Dynamical development of long-range spatial coherence in non-equilibrium bosonic condensation

Bianca Rae Fabricante, Dąbrówka Biegańska, Paolo Comaron et al. (+14 more)

Development of spontaneous coherence is one of the hallmarks of bosonic condensation in a variety of physical systems, such as cold atoms, confined photons, and hybrid light-matter quasiparticles like exciton polaritons in semiconductors. While spatial coherence is well understood once a steady-state condensate has been established, its temporal evolution as the condensate forms is largely unexplored. Here, we explore the dynamical formation of a non-equilibrium, driven-dissipative exciton-polariton condensate through both time-resolved experiments and numerical modeling. Our study reveals that the spatial coherence is established through two distinct stages. The early-time stage is interaction-driven and features transient oscillations in spatial coherence. This stage is followed by a steady-state regime characterized by a spatially-uniform high degree of coherence that extends over the entire size of the system and persists over time. These stages of spatial coherence development occur in both free flowing and confined exciton-polariton systems that undergo a quench - rapid growth of the condensate starting from two different initial settings. Our study offers a deep insight into the process by which long-range spatial coherence is established in a non-equilibrium bosonic condensate.
Read the full abstract

All authors Bianca Rae Fabricante, Dąbrówka Biegańska, Paolo Comaron, Mateusz Król, Matthias Wurdack, Maciej Pieczarka, Mark Steger, David W. Snoke, Kenneth West, Daniele Sanvitto, Dario Ballarini, Dimitrios Trypogeorgos, Loren N. Pfeiffer, Andrew G. Truscott, Marzena Szymańska, Elena A. Ostrovskaya, Eliezer Estrecho

Tuesday 25 August

Quantum Gases

Roton Instability in Quantum Droplets with Finite-Range Soft-Core Interaction

Avra Banerjee

We investigate the emergence of roton instability in self-bound quantum droplets interacting via a finite-range soft-core potential modeled by a Heaviside step interaction. The ground-state properties are obtained by solving the extended Gross-Pitaevskii equation including Lee-Huang-Yang corrections with a nonlocal interaction term. The collective excitation spectrum reveals the formation and progressive softening of a roton minimum as the interaction strength and range increase. When the roton energy approaches zero, the system becomes unstable, signaling the onset of density modulation. The rotonic behavior is further characterized through the static structure factor, which exhibits pronounced peaks at the roton momentum.
Read the full abstract

Quantum Gases · Cross-listed from cond-mat.mes-hall

Long-Range Order and Composite Boson Condensation in Lattice Quantum Hall States

Fabian J. Pauw, Nathan Goldman and Felix A. Palm

Topological states of matter, such as quantum Hall states, are characterized by the absence of local order parameters. In the continuum, their topological order has been reinterpreted as the condensation of nonlocal composite bosons, but this condensation and the resulting long-range correlations have so far eluded direct confirmation beyond the simplest trial states. Here, we apply tensor-network methods to lattice Hamiltonians hosting quantum Hall states, revealing this exotic order directly in interacting ground states and demonstrating both the long-range correlations and the condensation of composite bosons. These correlations define a nonlocal order parameter that identifies phase transitions between trivial and topological phases, for both bosonic and fermionic models. The corresponding operators are accessible through site-resolved, local measurements on an extensive number of particles, making them directly probable in quantum simulators. Our work opens new avenues for microscopic studies of topological quantum matter beyond the reach of traditional solid-state approaches.
Read the full abstract

Quantum Gases · Cross-listed from quant-ph

Tunable-Size Unruh-DeWitt Detector in a Multimode Cavity

Simon Brunner, Farokh Mivehvar, Helmut Ritsch et al. (+1 more)

Quantum simulators based on Bose-Einstein condensates (BECs) provide a powerful platform to study relativistic quantum-field phenomena in the lab and in particular emulate relativistic analog particle detectors. However, such detectors typically couple to excitations beyond the acoustic phonon regime, so that the nonlinear Bogoliubov dispersion introduces corrections that cause the effective relativistic description to break down. We propose to overcome this limitation using an intrinsically momentum-selective Unruh-DeWitt detector model in which a tweezer-trapped atom couples to the condensate through a multimode optical cavity. Although the atom is effectively pointlike, the cavity-mediated interaction kernel causes it to sample density fluctuations over a controllable finite region of the BEC equivalent to a finite-size detector. The effective detector size is tunable via the cavity mode structure determining a controllable momentum cutoff that filters out nonphononic excitations. We analytically calculate the response of such a detector for uniform linear acceleration and uniform circular motion and show that this momentum selectivity can enhance the signal at experimentally accessible accelerations. Compatible with existing cavity-QED platforms our scheme thus provides a versatile setting for analog quantum-field measurements or relativistic quantum-information protocols.
Read the full abstract

All authors Simon Brunner, Farokh Mivehvar, Helmut Ritsch, Arkadiusz Kosior

Quantum Gases · Cross-listed from nlin.PS

Stable rotating vortex clusters in three-dimensional quantum droplets

Liangwei Dong and Yaroslav V. Kartashov

We predict a new type of stable three-dimensional (3D) vortex quantum droplets in binary Bose-Einstein condensate arranged into ring clusters that per-sistently rotate in the external potential. In contrast to clusters composed from localized quantum droplets, the states introduced here represent interacting vortex lines with identical topological charges nested in common 3D envelope and existing in much broader parameter range in comparison with local-ized quantum droplets. The intricate interplay between mean-field nonlinearity of Bose-Einstein condensate, quantum fluctuations described by Lee-Huang-Yang correction, Coriolis force arising due to rotation, and external potential leads to substantial variations of cluster shape upon increase of its rotation frequency. Rotating vortex clusters bifurcate from single-vortex quantum droplets and exist only above critical value of the rotation frequency that decreases with increase of chemical potential and depends on the number of vortex lines in the cluster. The radius of the cluster decreases with increase of rotation frequency and weakly varies with chemical potential, which determines mostly localization of the individual vortices in cluster and overall width of its envelope. Vortex droplet clusters are very robust objects existing in stable form in wide intervals of the number of particles for any number (odd or even) of vortex lines forming them. Our results may open the route to observation of stable arrays of vortex lines of different configurations per-forming regular collective motion in condensate.
Read the full abstract

Quantum Gases

Tunable Mediated Interactions Near Spontaneous Symmetry Breaking: From Yukawa to Coulomb and Dzyaloshinskii–Moriya Interactions

Hoshu Hiyane and Hiroyuki Tajima

We propose a realization of tunable long-range mediated interactions generated by Nambu-Goldstone (NG) modes near spontaneous symmetry breaking. An effective exchange interaction emerges between two distinguishable impurities proportional to the retarded susceptibility mediated by the bath particles. The interaction is mediated by emergent NG modes associated with symmetry breaking in systems, namely the magnon mode in a repulsive two-component Fermi or Bose gas, or the goldstino mode in a Bose-Fermi mixture. When the NG mode is gapped by explicit symmetry breaking, the interaction has a Yukawa-type short-ranged interaction, whereas the gapless limit gives a Coulomb law. Above the NG mode threshold, the Dzyaloshinskii-Moriya-like cross product coupling emerges in a long-range form. Our proposal paves a way towards the realization of a quantum simulator of spin models and polarons with controllable non-local interactions.
Read the full abstract

Monday 24 August

Quantum Gases · Cross-listed from cond-mat.mes-hall

A Simple Regularization of the Smooth Quantum Hydrodynamic Model

Carl L. Gardner

A simple regularization of the smooth quantum hydrodynamic model equations to prevent an unstable growing mode is proposed. The regularization involves replacing the spatial derivative of the electron density on the right-hand side of the momentum conservation equation by using the classical Boltzmann distribution for electron density. Time-dependent simulations of the resonant tunneling diode to steady state using this regularization are presented, which show realistic negative differential resistance (the experimental signal of quantum resonance) and hysteresis in the current-voltage curve. The simulations are in good agreement with fully quantum mechanical simulations of the resonant tunneling diode.
Read the full abstract

Quantum Gases · Cross-listed from physics.atom-ph

Multi-hour stable trapping and threshold steady state of non-laser-coolable ions with ultracold atoms in a hybrid trap

Satyabrata Baidya and Sourav Dutta

We report multi-hour stable trapping and steady state of non-laser-coolable Cs$^{+}$ ions in a linear Paul trap, achieved via resonant charge-exchange (RCE) cooling with a precisely centered ultracold Cs cloud. Without cold atoms, all ions are lost within 3 minutes. With centered cold atoms, RCE cooling establishes a stable population of ions for 6 hours with no measurable decay – more than two orders of magnitude longer hold times compared to prior hybrid atom-ion systems. We observe a threshold behavior in the steady-state number of ions ($N_{s}$): initial ion loadings above $N_{s}$ ions converge downward to $N_{s}$ ions and remain constant thereafter; initial loadings below $N_{s}$ ions show no measurable decay. The dynamics is governed by a competition between ion-ion rf heating and ion-atom collisional cooling. The prolonged, simultaneous ion-atom trapping suggests an upper bound on the three-body recombination-induced Cs$_{2}^{+}$ formation rate constant: $k_{3} << 1.4 \times 10^{-25} cm^{6} s^{-1}$. This remarkable realization of long-lived steady state overcomes a critical limitation of prior hybrid atom-ion systems and enables extended studies of ultracold ion-neutral chemistry, rare inelastic collisions, and sympathetic cooling routes for complex molecular ions.
Read the full abstract

Quantum Gases

Observation of electron spin interactions between Rydberg atoms

Le Ruan, Ziqi Zhou, Yuchen Guo et al. (+2 more)

We report the observation of electron spin interactions between Rydberg atoms, which are driven by spin-orbit coupling through second-order dipole perturbation and exhibit a spatial anisotropy governed by the atomic configuration. Specifically, we observe coherent electron spin exchange dynamics, with the measured coupling strength agreeing well with both numerical calculations and theoretical models. Furthermore, we show that global microwave dressing enables active engineering and dynamical freezing of the spin exchange by introducing a differential AC Stark shift between the participating states. Additionally, we achieve tunability of the interaction by applying a stronger magnetic field, which effectively modifies the energy contributions of the underlying spin-orbit coupling channels. Finally, measuring spin dynamics in one-dimensional multi-atom chains aligned parallel or perpendicular to the magnetic field provides a self-consistent validation of the anisotropic XXZ framework. This electron spin interaction natively features spin-position coupling and enables a natural mapping onto the Heisenberg-Kitaev model. Our findings reveal a new class of electron spin-spin interactions among Rydberg atoms, expanding the scope of quantum simulation with Rydberg atom arrays.
Read the full abstract

All authors Le Ruan, Ziqi Zhou, Yuchen Guo, Chengshu Li, Cheng Chen

Quantum Gases

Universal Spin-Position Coupled Rydberg Interactions

Chengshu Li and Hui Zhai

Strong interactions between $s$-orbital Rydberg atoms underpin atom-array-based quantum computation and quantum simulation. Typically, the spin dependence of these interactions is negligible and plays no practical role. In this Letter, we uncover that a strong electron-spin-dependent Rydberg interaction can emerge when the principal quantum numbers of the two $s$-orbital atoms differ by a sweet-spot value. This interaction originates from the fine-structure splitting of nearby $p$ orbitals, which endows it with distinct symmetry properties such that the electron spins are coupled to the relative position of the two atoms, featuring a spatially defined anisotropy. We further demonstrate that this interaction admits a universal form, independent of the principal quantum numbers, and highlight its fundamental distinction from conventional magnetic dipolar interactions, establishing it as a new type of native magnetic interaction in nature. Our findings introduce a new element to the Rydberg quantum simulation toolbox. As a concrete application, we propose a native realization of the Kitaev-Heisenberg model, which hosts an unusual stripe phase as a quantum many-body manifestation of spin-space locking.
Read the full abstract

Quantum Gases

Spinor condensate persistent currents in an atomtronic Josephson necklace

Sayan Chatterjee, Nalinikanta Pradhan, Rina Kanamoto et al. (+2 more)

The investigation of superflow in multi-junction Josephson circuits is currently a leading frontier of physics research, probing the fundamental manifestations of macroscopic phase coherence and enabling applications to quantum simulation, metrology and computing. In this work, we extensively investigate the stability and dynamics of persistent currents of a spinor atomic Bose-Einstein condensate on a ring with multiple Josephson junctions. Specifically, we examine the effects of positive and negative interspecies interactions, co- and counter-rotation, population and Manakov asymmetry, as well as Rabi coupling on the persistent currents carried by the two components. Our analysis reveals that the presence of a second species offers multiple mechanisms for unprecedented manipulation of supercurrents on the ring, including phase-slip engineering, stability control, current-inversion switching and supercurrent pumping. Our study provides a roadmap for the engineering of persistent currents in binary ring condensates in necklace potentials, with significant implications for atomtronics, matter-wave interferometry and sensing using atomic Bose gases.
Read the full abstract

All authors Sayan Chatterjee, Nalinikanta Pradhan, Rina Kanamoto, M. Bhattacharya, Pankaj Kumar Mishra

Quantum Gases · Cross-listed from quant-ph

Dissipation-induced Sachdev-Ye-Kitaev physics in many-body cavity quantum electrodynamics

Pietro Pacchioni, Filippo Ferrari, Vincenzo Savona et al. (+1 more)

We show that cavity quantum electrodynamics (QED) devices can realize dissipative Sachdev-Ye-Kitaev (SYK) universality, a paradigmatic setting for quantum chaos in open many-body systems. Ultracold fermions with disordered, all-to-all cavity-mediated interactions provide two complementary routes: atomic spontaneous emission in a single-mode cavity and photon leakage from a multimode cavity. Strikingly, both converge to the same non-Hermitian random-matrix universality despite originating from integrable and chaotic closed-system limits, respectively. In the single-mode cavity, dissipation creates quantum chaos from an integrable Hamiltonian. We trace this convergence to a tunable growth in dissipative rank, controlled, respectively, by the Lamb-Dicke parameter and the cavity-mode spacing. The integrability-to-chaos crossover is accompanied by a dynamical crossover from long-lived prethermal memory to rapid thermalization, visible in single-atom-resolved densities.
Read the full abstract

All authors Pietro Pacchioni, Filippo Ferrari, Vincenzo Savona, Matteo Seclì

Quantum Gases · Cross-listed from cond-mat.mes-hall

Quaternionic Hermitian Band Geometry in Four Dimensions: Realization on $S^4$ and Obstruction on $T^4$

Dongju Hwang, Minjae Yu and Gil Young Cho

We establish a realization-obstruction dichotomy for quaternionic Hermitian band geometry in four-dimensional parameter spaces: the minimal-charge lowest Landau level on $S^{4}$ provides a global realization, whereas an everywhere nondegenerate saturated realization induced by a single occupied quaternionic band is obstructed on $T^{4}$. An antiunitary symmetry $\mathcal{J}$ satisfying $\mathcal{J}^{2}=-1$ makes the occupied doublet a quaternionic band. Within this setting, we formulate the quaternionic Wirtinger inequality as a band-geometric bound involving the quantum metric and the second Chern density. At every nondegenerate saturation point, the canonical geometry of the quaternionic projective space pulls back to a compatible quaternionic structure on the parameter space; if these conditions hold everywhere, the parameter space acquires quaternionic Hermitian band geometry. On $S^{4}$, we express the minimal-charge states as quaternionic Perelomov coherent states and establish everywhere nondegenerate saturation, thereby realizing quaternionic Hermitian band geometry. On $T^{4}$, by contrast, a minimal four-band system saturates the inequality everywhere, but topology forces the quantum metric to become degenerate somewhere, obstructing a globally induced quaternionic structure. An explicit lattice Dirac Hamiltonian exhibits this obstruction. Adding unoccupied bands cannot remove this obstruction when the inequality is saturated everywhere, since the image of any nondegenerate saturated projector remains confined to a fixed $\mathbb{H}P^{1}$. These results provide a symmetry-aware framework for non-Abelian band geometry and show how parameter-space topology constrains the global realization of quaternionic Hermitian band geometry.
Read the full abstract

Sunday 23 August

Quantum Gases · Cross-listed from nlin.PS

Dynamics of Flat-Top–Bubble Vector Solitons

M. O. D. Alotaibi, L. Al Sakkaf and U. Al Khawaja

We investigate the dynamics of two-component flat-top–bubble vector solitons using a variational approximation and numerical simulations. The system is described by coupled cubic-quintic nonlinear Schrödinger equations with repulsive intercomponent coupling. We introduce a self-induced mechanism in which a localized flat-top soliton (FTS) generates a density bubble in a second component: the localized density acts as a repulsive potential for the background field, creating a composite bound state. A background-subtracted formulation and normalized super-Gaussian profiles yield collective-coordinate equations for the component centers and an effective interaction potential for their relative separation. The potential forms a binding well that is nearly triangular over its global displacement range but smooth and locally parabolic near its minimum. The variational approximation consequently predicts harmonic internal oscillations whose frequency is independent of amplitude in the small-oscillation regime. Real-time simulations verify this weak-kick behavior with good agreement between the variational and numerical frequencies. For strong phase imprints, equating the exact kick energy to the variational binding depth predicts a kick scale \(K_{\mathrm{escape}}\) for the onset of partial FTS escape. Real-time simulations support this prediction: below this scale, the composite remains nearly intact, whereas above it, a substantial fraction of the localized component leaves the bubble.
Read the full abstract

Quantum Gases · Cross-listed from cond-mat.mes-hall

Coordinate transformations and matter waves cloaking

Reza G. Mohammadi, Ali G. Moghaddam and Ramin Mohammadkhani

Transformation method provides an efficient tool to control wave propagation inside the materials. Using the coordinate transformation approach, we study invisibility cloaks with sphere, cylinder and ellipsoid structures for electronic waves propagation. The underlying physics behind this investigation is the fact that the Schrödinger equation with position-dependent mass tensor and potentials has a covariant form that follows the coordinate transformation. Using this technique we obtain the exact spatial form of the mass tensor and potentials for a variety of cloaks with different shapes.
Read the full abstract

Saturday 22 August

Quantum Gases

Odd-frequency pair correlations in the trapped fermionic Tonks-Girardeau gas

M. Wong, K. Thompson, M. Governale et al. (+2 more)

The fermionic Tonks-Girardeau gas is an exactly solvable model realizing a conventional macroscopic condensate of p-wave Cooper pairs. Here we demonstrate that, when confined by a trapping potential, it also hosts unconventional odd-frequency pairing, i.e., pair correlations with s-wave symmetry that are only present with a finite time delay t between fermions forming a pair. Quantitative results for fixed particle number are obtained using a generalization of Yang's theory of off-diagonal long-range order to define a t-dependent order parameter that is antisymmetric under combined t inversion and exchange of fermion-pair indices. Odd-frequency pairing in the fermionic Tonks-Girardeau gas is found to be a mesoscopic effect, localized at the system's boundary and therefore nonextensive thermodynamically. Our results show that this elusive hidden order is accessible in systems having fixed particle number, suggesting new avenues towards its experimental realization and further detailed study.
Read the full abstract

All authors M. Wong, K. Thompson, M. Governale, J. Brand, U. Zuelicke

Quantum Gases

Breakdown of Aharonov-Bohm cage in Rydberg synthetic lattices: the roles of inhomogeneity and long-range exchange

Li Pan, Xinlu Chen, Hong Zhang et al. (+1 more)

While the interaction-induced breakdown of Aharonov-Bohm (AB) cage is typically attributed to uniform bound-pair transport, systems with inhomogeneous exchange interactions realized with Rydberg synthetic lattices exhibit more complex dynamics. Employing the evolution-path symmetry (EPS) framework developed recently, we analyze the two-particle dynamics via path interference in Fock space. We find that a homogeneous nearest-neighbor exchange interaction cannot break the AB cage, regardless of whether the long-range exchange interaction is present or not. In contrast, we demonstrate that inhomogeneous nearest-neighbor exchange interaction breaks the destructive-interference EPS, and lifts the degeneracy of many-body compact localized states, thereby generating non-local dispersive eigenstates. Consequently, the initial state gains a non-zero overlap with these dispersive states, enabling delocalized transport. Furthermore, while long-range exchange interaction alone preserves the AB cage, its coupling with nearest-neighbor inhomogeneous exchange interaction opens non-canceling pathways that alter the diffusion profile. Our work connects microscopic path interference with macroscopic spectral reorganization, offering an analytical understanding of the mechanism underlying exchange-interaction-induced transport in Rydberg synthetic lattices.
Read the full abstract

All authors Li Pan, Xinlu Chen, Hong Zhang, Jian-Song Pan

Friday 21 August

Quantum Gases

Dynamical Signatures and Kibble-Zurek Scaling of Localization in Tilted Bose-Einstein Condensates

Argha Debnath, Radheshyam Saha, Ravindra W. Chhajlany et al. (+2 more)

We study nonequilibrium signatures of tilt-induced localization in a one-dimensional Bose-Einstein condensate loaded in a shallow optical lattice. The tilt strength acts as a control parameter for the localization-delocalization crossover. We also consider the effects of repulsive interactions, which tend to delocalize the condensate. We first characterize localized and delocalized regimes through sudden quenches of the interaction strength and the external tilt. The resulting dynamics is analyzed using the survival probability and its power spectral density. Localized condensates exhibit strong memory retention, pronounced revivals, regular dynamics and a narrow spectral response, whereas delocalized condensates show suppressed recurrences, irregular dynamics and a broader distribution of spectral weight over many frequencies. We then investigate finite-rate ramps of the tilt strength across the localization threshold. Using the localization length and the Bogoliubov excitation gap, we extract the relevant critical exponents and perform Kibble-Zurek scaling analysis in the driven dynamics. Our results establish quench response and finite-rate scaling as complementary dynamical probes of localization in interacting Bose gases, with direct relevance to cold-atom experiments in tilted optical lattices.
Read the full abstract

All authors Argha Debnath, Radheshyam Saha, Ravindra W. Chhajlany, Mariusz Gajda, Debraj Rakshit

Quantum Gases · Cross-listed from cond-mat.supr-con

Electrostatic lens of a charged vortex

Iogann Tolbatov and Luca Salasnich

We study the local electrostatic response of a charged superfluid in the presence of a cylindrically symmetric vortex, allowing both the particle density and the thermodynamic compressibility to vary with the radial coordinate. Starting from the electrostatic charge response obtained from the phase-only Popov action, we introduce a local-density extension and derive the regular near-axis expansion of the scalar potential. The constant, quadratic, and quartic coefficients are obtained explicitly in terms of the local screening response and of the leading nonuniform contribution to the vortex density profile. For a three-dimensional unitary Fermi equation of state, the density dependence of the compressibility generates a definite thermodynamic contribution to the quartic coefficient. The resulting decomposition separates this equation-of-state contribution from the ordinary constant-screening and charge-source terms that occur at the same order. This provides a compact analytical connection between vortex-core thermodynamics and the local electrostatic profile of a charged superfluid.
Read the full abstract

Quantum Gases

Quantum Fisher information in a quenched $p + ip$ superfluid

Stelio Varrone and Yunxiang Liao

The quantum Fisher information (QFI) is widely used to characterize quantum phases and transitions, but its diagnostic power sometimes relies on selecting special generators based on prior knowledge of the underlying physics. We ask whether this requirement can be relaxed in nonequilibrium systems by studying the QFI of the long-time asymptotic state of a two-dimensional p+ip superfluid following an instantaneous quench of the coupling strength, using the particle number within a large subextensive subsystem as the generator. In equilibrium, the ground-state QFI is continuous across the topological transition between the weak-pairing BCS and the strong-pairing BEC phases, showing no direct signature of the transition. After the quench, however, the QFI associated with the same generator distinguishes the three dynamical phases and can encode the topology of the pre-quench state. In phase I, with a vanishing order parameter, the QFI Fourier spectrum consists of a single zero-frequency spike determined by the nonequilibrium distribution function. In phase II, with a constant nonzero order parameter, the QFI spectrum contains a zero-frequency spike and two continua separated by a gap set by the minimum asymptotic quasiparticle energy. The continuum edge behavior reveals whether this minimum occurs at zero or finite momentum. In the former case, the spectral weight vanishes at the edge, with the sign just inside the continuum encoding the pre-quench topology for large subsystem. In phase III, with a time-periodic order parameter, the QFI spectrum exhibits discrete peaks at integer multiples of the oscillation frequency, together with continua associated with the Floquet quasienergy spectrum. Our results show that driving the system out of equilibrium can enhance the diagnostic power of the QFI for a standard physical observable, revealing information inaccessible in equilibrium.
Read the full abstract

Quantum Gases

Pair size versus coherence length and quantum geometry in the spin-orbit coupled BCS-BEC crossover

R. N. Kalkan and M. Iskin

We investigate the interplay between pairing correlations and quantum geometry in the spin-orbit-coupled BCS-BEC crossover. Working in the helicity basis, we derive the exact pair-size tensor for the two-body bound states and show that it separates into intraband and quantum-geometric interband contributions, with the latter determined by the quantum metric. We extend this decomposition to two distinct many-body length scales at zero temperature: the Cooper-pair size, obtained from mean-field BCS theory, and the coherence length, obtained from the Gaussian fluctuation theory. Although these quantities almost coincide in the BCS regime, they describe distinct physical properties away from it, with the pair size characterizing the internal extent of a pair and the coherence length characterizing the long-wavelength response of the order parameter. We evaluate both quantities for three-dimensional Rashba, three-dimensional Weyl, and two-dimensional Rashba spin-orbit coupling models. We find that the pair size decreases monotonically with increasing spin-orbit coupling as the pair localizes, whereas the coherence length develops a pronounced minimum in the crossover regime before growing again in the BEC regime as the composite bosons become weakly interacting. This minimum is tied to the collapse of the noninteracting Fermi surface onto the ring or sphere of helicity-band minima. The quantum-geometric contributions reach up to nearly one third of the pair size and about 40% of the coherence length, tracking these same changes in the underlying helicity Fermi-surface topology.
Read the full abstract

Quantum Gases · Cross-listed from quant-ph

Characterizing Multimode Effects in a Guided Matterwave Gyroscope

Jessica K. Eastman, Ellen Zheng, Stuart S. Szigeti et al. (+1 more)

We theoretically investigate the performance of a compact matterwave vortex gyroscope formed by a two-component Bose-Einstein condensate in a toroidal potential. Unlike conventional atomic gyroscopes that rely on the Sagnac effect, the topological stability of the vortex state yields rotation sensitivity independent of the enclosed area, making the device robust against geometric drifts. Using fully quantum multimode simulations, we quantify two interaction-driven mechanisms that degrade performance: phase diffusion from one-axis-twisting and four-wave mixing from intercomponent scattering. We identify regimes where tuning interaction and trapping parameters produces a trade-off between these effects, and find that reducing the intercomponent scattering length can counterintuitively worsen sensitivity. Finally, we compare the vortex gyroscope to a guided Sagnac interferometer, demonstrating superior scaling, establishing it as a promising candidate for compact precision rotation sensing.
Read the full abstract

All authors Jessica K. Eastman, Ellen Zheng, Stuart S. Szigeti, Simon A. Haine

Thursday 20 August

Quantum Gases · Cross-listed from cond-mat.stat-mech

Power Series for the Quantum Statistical Mechanics Probability with Results for the Second Virial Coefficient of Helium

Phil Attard

A power series for the Wigner-Kirkwood pair commutation function for quantum statistical mechanics in classical phase space is given with terms automatically generated by recursion. The calculated second virial coefficient agrees with the measured values of helium for temperatures greater than 65 K. Prospects for a general quantum Monte Carlo algorithm are discussed.
Read the full abstract

Quantum Gases

Photon-mediated thermodynamics and density fluctuations in an ensemble of laser-cooled Cesium atoms

Arnab Ghosh, Inderpreet Kaur, Hemant Yadav et al. (+5 more)

We present an experimental study of detuning-dependent properties of a laser-cooled cesium cloud in a magneto-optical trap. Fluorescence images are used to extract the cloud size, shot-to-shot width fluctuations, optical depth, density profiles, and spatial density fluctuation spectra as the trapping-laser detuning is varied. Near resonance, the cloud exhibits larger spatial extent, increased width fluctuations, higher optical depth, and enhanced density-fluctuation power, while larger detunings produce a more reproducible and spatially confined cloud. The measured density profiles are analysed phenomenologically using a generalized Lane-Emden model with a polytropic equation of state, yielding detuning-dependent effective fit parameters in a weak-interaction regime. Power-spectrum and autocorrelation analyses reveal reproducible scale-dependent density correlations. The results provide a quantitative characterization of detuning-dependent radiative and collective effects in a cesium MOT and establish a basis for future measurements that can more directly test nonequilibrium transport and photon-mediated interaction models.
Read the full abstract

All authors Arnab Ghosh, Inderpreet Kaur, Hemant Yadav, Shiva Kant Dwivedi, R Shanmukesh, Mithun Thudiyangal, Matthew J. Davis, Bodhaditya Santra

Quantum Gases

Self-limiting electrostriction of a single ion in an ultracold polar gas: From mesoscopic ions to crystalline molecular rings

Ruiren Shi, Saajid Chowdhury, Leon Karpa et al. (+1 more)

We investigate the self-assembly of polar molecules around a single ion immersed in an ultracold, dilute two-dimensional molecular gas. The ion aligns and attracts the molecules through charge-dipole interactions, producing a strong electrostrictive accumulation around the impurity, while intermolecular repulsion limits further densification and favors spatially extended configurations. By combining global optimization with diffusion Monte Carlo, we calculate the evaporation energy as a function of the number of molecules bound to the ion. In contrast to conventional charged and van der Waals clusters, the evaporation energy exhibits a plateau-like dependence on cluster size, reflecting the sequential formation of concentric molecular rings. These structures are governed by the topology of the ion's electric field and by the competition between attractive ion-molecule interactions, repulsive intra-ring interactions, and attractive correlations between neighboring rings, rather than by conventional coordination or icosahedral packing. In the weak-interaction regime, the resulting structures form extended mesoscopic molecular ions, whereas stronger interactions produce increasingly rigid, crystal-like molecular rings. We further analyze their stability against thermal perturbations and the time-dependent ion trap and find that a broad range of clusters remain stable under experimentally relevant conditions. The intermolecular repulsion and dipolar geometry also suppress close-range ion-molecule encounters, suggesting an intrinsic shielding mechanism. Our results establish ion-bound polar-molecule clusters as a distinct class of mesoscopic molecular ions and open a route to studying charged impurities in quantum baths with anisotropic interactions.
Read the full abstract

All authors Ruiren Shi, Saajid Chowdhury, Leon Karpa, Jesús Pérez-Ríos

Quantum Gases · Cross-listed from physics.atom-ph

A Protocol for Shielding-Enhanced Loading of Single Polar Molecules into Optical Tweezers

Reuben R. W. Wang, Christian H. Nunez, Conner Williams et al. (+4 more)

We propose the high-fidelity preparation of single bosonic molecules in optical tweezers starting from small tweezer-trapped molecular ensembles. Our scheme combines a static electric field and a microwave field to generate strong, tunable, anisotropic interactions that shield the molecules against two-body collisional loss. We show that this shielding eliminates all long-range bound states, preventing three-body recombination. This elimination persists for all microwave ellipticities, including the experimentally practical limit of linear polarization. Application of an additional electric field gradient can be used to induce controlled spilling of strongly interacting molecules out of the trap until one remains. With realistic experimental parameters, we estimate that single tweezer-trapped NaCs molecules can be isolated from a pair with fidelities exceeding 99%, and $> 95\%$ per site across an array. These results establish collisional shielding with electric fields as an effective tool for preparing highly-filled tweezer arrays of polar molecules.
Read the full abstract

All authors Reuben R. W. Wang, Christian H. Nunez, Conner Williams, Amanda Younes, Li Du, H. R. Sadeghpour, Kang-Kuen Ni

Quantum Gases

Competing triangular and stripe supersolid orders in a dipolar quantum gas

Karthik Chandrashekara, Christian Gölzhäuser, Lily Platt et al. (+6 more)

Supersolids are exotic quantum states in which long-range phase coherence coexists, and may interplay, with emergent spatial orders. A particularly rich phase diagram featuring several competing spatial orders is predicted for dipolar supersolids with two-dimensional crystals, yet the experimental observation of this structural variety has remained limited. Here we experimentally form competing triangular and stripe density-modulated states in a quantum gas of highly magnetic atoms confined in a surfboard-shaped trap by tuning contact interaction strength and dipole orientation. We define a structural order parameter and study its statistical behavior. Thereby, we identify both the triangular and stripe phases and the transition between them, the associated critical behavior being marked by enhanced non-Gaussian fluctuations. Furthermore, we observe each spatial structure in both the phase-coherent supersolid regime and the phase-incoherent insulating one, near and far from the unmodulated-to-modulated transition, respectively. Our results establish a versatile platform in which multiple phases of the two-dimensional-supersolid phase diagram, and more generally, intertwined symmetry-breaking phenomena, can be investigated.
Read the full abstract

All authors Karthik Chandrashekara, Christian Gölzhäuser, Lily Platt, Jianshun Gao, Julian Kusch, Lennart Hoenen, Manon Ballu, Wyatt Kirkby, Lauriane Chomaz

Quantum Gases

Imaging the vacuum fluctuations of a quantum field

Yansheng Zhang, Feiyang Wang, Yi Jiang et al. (+5 more)

Heisenberg uncertainties lead to inevitable fluctuations in the measurement outcomes for quantum-mechanical observables. For quantum fields, these uncertainties result in random spatial structures in snapshots of a field, even when the field is in its ground (vacuum) state. Such `vacuum fluctuations' are at the heart of a wide range of phenomena, from spontaneous decay processes to the Casimir force and Hawking radiation. Their existence is a key manifestation of the quantumness of the physical world, but usually it is only their consequences that are directly observed. Here, we directly observe spatial vacuum fluctuations of a bosonic quantum field. Our experiments are based on a homogeneous planar atomic Bose–Einstein condensate. The condensate comprises two coherently coupled interacting components (spin states), and the quantum field describes its spin degrees of freedom. In the regime where the interactions dominate over the coherent coupling, our system emulates a (massive relativistic) sine-Gordon field. Images of the field reveal simultaneous fluctuations on different length scales, with scale-dependent amplitudes consistent with theoretical predictions for a vacuum state. Observing such fluctuations in the sine-Gordon limit opens many possibilities for laboratory simulations of relativistic fields in regimes that are presently not theoretically tractable.
Read the full abstract

All authors Yansheng Zhang, Feiyang Wang, Yi Jiang, Alexander C. Jenkins, Paul H. C. Wong, Christoph Eigen, Gehrig Carlse, Zoran Hadzibabic

Quantum Gases · Cross-listed from cond-mat.mes-hall

Signatures of a light-induced exciton condensate exhibiting BEC-BCS crossover

Khanh Duy Nguyen, Gabriele Berruto, Yunhe Bai et al. (+7 more)

Exciton condensates provide a platform to study quasiparticle pairing, Bose-Einstein condensation-Bardeen-Cooper-Schrieffer (BEC-BCS) crossover, and excitonic topological phenomena. Achieving a nonequilibrium exciton condensate allows the ultimate tunability of these emergent phenomena. Yet, evidence of a light-induced, nonequilibrium exciton condensate and its BEC-BCS crossover remains elusive. Here, we use time- and angle-resolved photoemission spectroscopy to demonstrate signatures of a non-equilibrium exciton condensate and its BEC-BCS crossover in monolayer MnBi2Te4. Following optical excitation, a distinctive hole-like dispersion representing excitons emerges and persists for >20 ps. Strikingly, energy-domain sharpening in the valence band occurs 2 ps after time zero and exhibits a sharp onset at a threshold pump fluence of 0.84 mJ/cm2. The delayed and strongly nonlinear response is difficult to reconcile with transient field effects or conventional carrier-induced band shifts but is consistent with a model of exciton condensation governed by a Berezinskii-Kosterlitz-Thouless transition. The estimated threshold exciton density agrees quantitatively with the Nelson-Kosterlitz critical density. At higher fluences, the exciton feature develops a camel-back-shaped dispersion, consistent with the BEC-BCS crossover in the condensate framework. Our work establishes ultrathin MnBi2Te4 as a model system for studying nonequilibrium exciton condensates with a connection to superconductivity and exciton-driven topological phases.
Read the full abstract

All authors Khanh Duy Nguyen, Gabriele Berruto, Yunhe Bai, Thomas Marchese, Woojoo Lee, Haoran Lin, Jiangang Yang, Chong Liu, Y. Shirley Meng, Shuolong Yang

Quantum Gases · Cross-listed from quant-ph

Programmable cavity QED with a fiber-integrated atomic array

Stephan Roschinski, Johannes Schabbauer, Franz von Silva-Tarouca et al. (+3 more)

Strong atom-photon interactions in optical cavities are a key resource for quantum information processing, quantum networking, and the exploration of quantum optical effects. Optical tweezer arrays offer scalable, site-resolved control of neutral atoms, but their integration with high-cooperativity cavity QED systems remains challenging. Here we combine a twelve-site $^{87}$Rb optical tweezer array with a high-cooperativity fiber Fabry-Pérot microcavity. The array is positioned within the cavity mode and individual sites are controlled with subwavelength precision, enabling continuous tuning of the single-atom coupling strength via deterministic displacement through the standing-wave field. For up to five atoms coupled to the cavity, we measure collectively enhanced vacuum Rabi splitting and implement cavity-based non-destructive readout of the number of coupled atoms. These results establish a scalable architecture for cavity-mediated entanglement generation and many-body cavity QED with single-atom control, and they lay the foundation for fiber-integrated quantum network nodes.
Read the full abstract

All authors Stephan Roschinski, Johannes Schabbauer, Franz von Silva-Tarouca, Marvin Holten, Damien Bloch, Julian Léonard