Quantum Gases · Cross-listed from cond-mat.mes-hall
Papers
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Wednesday 12 August
Excitons provide a promising platform for the realization of solid-state Bose-Einstein condensation (BEC), offering quantum coherence, strongly correlated electron-hole physics, and superfluidity. Yet, its unambiguous experimental identification remains challenging. In particular, $S_z= \pm 1$ triplet excitons are excellent candidates to realize an exciton BEC, because of their intrinsically limited recombination rate and thus long lifetimes. However, since their optical detection is inherently forbidden, experimental signatures remain elusive. In this work, we demonstrate that the magnetic nature of a $S_z= \pm 1$ triplet exciton BEC gives rise to stray magnetic field noise, that can be measured using nitrogen-vacancy (NV) center magnetometry. Using an external magnetic field to tune the system from an antiferromagnetic to a ferromagnetic ordering, the longitudinal spin sound mode of the BEC softens, bringing the mode into the characteristic gigahertz frequency range of the NV spin relaxation rate and thus allowing direct detection. Furthermore, we demonstrate an unconventional UV scaling at small distances $d$ from the sample, owing to the cubic corrections to the sound mode dispersion and damping rate in the form of Beliaev damping. Through this approach, we establish that the spin component of exciton BECs offers new approaches to detect exciton BECs.
Quantum Gases
Fluctuation Spectra and Response Function of Coupled Atomic and Molecular BECs
We investigate out-of-equilibrium properties of atomic molecular Bose Einstein condensates coupled through a Feshbach resonance, with the Feshbach coupling and detuning subject to Gaussian white noise. Using a bosonic Josephson junction framework and a Bloch sphere description, we examine the interplay of detuning, coherence, and noise governing the system dynamics. Coupling and detuning noise produce distinct fluctuation spectra, featuring both Feshbach resonant and symmetric off resonant peaks. We characterize the dispersive and absorptive response of the atom dimer system under periodic driving. The atom molecule hybridization at the Feshbach resonance maximizes the linewidth and minimizes both the effective temperature and the phase difference between the driving field and the system. This leads to an optimized power utilization and quality factor.
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Tuesday 11 August
Quantum Gases
OpenMP Fortran programs for rotating dipolar Bose-Einstein condensates
In this paper we present Open Multi-Processing (OpenMP) Fortran 90/95 programs to solve the Gross-Pitaevskii equation for a rotating dipolar Bose-Einstein condensate (BEC) in two and three dimensions, which is a new version of our previous published programs for a dipolar Bose-Einstein condensate without rotation. After the recent experimental study of a rotating dipolar BEC [L. Klaus et al., Nature Phys. 18, 1453 (2022)], the present programs will be useful tools for related theoretical investigation. The algorithm used is the split-step semi-implicit Crank-Nicolson scheme for imaginary- and real-time propagation to obtain stationary states and BEC dynamics, respectively, as in the previous version [L. E. Young-S. et al., Comput. Phys. Commun. 286 (2023) 108669].
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Quantum Gases
Composite-Boson Ansatz for Fractional Quantum Hall Manifolds of Lattice Bosons at Generic Fillings $\nu<1/2$
Hofstadter systems provide a lattice route to fractional quantum Hall physics, but their low-energy manifolds often lack simple wave-function descriptions. Here we present a composite-boson ansatz for a broad family of finite-size lattice-split Laughlin-quasihole manifolds in the low-flux Hofstadter–Bose–Hubbard model on a torus at generic fillings \(\nu<1/2\). Attaching two vortices to each boson yields reduced-flux orbitals from which we construct a many-body trial basis. Its translation-resolved rank reproduces the expected low-energy-manifold dimension and provides a composite-boson interpretation of the established quasihole counting previously inferred from generalized exclusion rules and thin-torus arguments. For smaller systems, diagonalization within the lowest-band-projected ansatz span closely reproduces the exact projected spectrum, while variational Monte Carlo extends the rank and energetic analysis to larger systems for which explicit subspace construction becomes costly. To probe the fractional quantum Hall character of these manifolds, we calculate their many-body Chern-numbers and show that localized added-flux excitations exhibit quasihole-like behavior, with fractional density depletion and an Aharonov–Bohm-free braiding phase that both track the effective filling. Together, these results establish a microscopic composite-boson framework for organizing a broad family of sub-half-filled fractional quantum Hall manifolds of lattice bosons.
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Quantum Gases
Two-component ultracold Bose gases with spin-orbit coupling
These lecture notes provide an introduction to Bose-Einstein condensates with Raman-induced spin-orbit coupling. Owing to the interplay between the peculiar single-particle dispersion, featuring a double-minimum structure, and the two-body interaction, these systems possess a complex phase diagram. Three different quantum phases can be observed, i.e., a stripe, a plane-wave, and a single-minimum phase, each characterized by different broken symmetries. The condensate dynamics is also significantly affected by the spin-orbit coupling, as revealed by the behavior of the Bogoliubov spectrum in infinite systems and the behavior of the discretized collective mode frequencies in trapped configurations, especially close to the phase transitions. In turn, the superfluid and rotational properties are also deeply modified by the coupling between the motional and spin degree of freedom. Finally, a special attention is devoted to the stripe phase and its supersolid character, which can be clearly revealed by the study of its dynamic features.
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Quantum Gases
Dynamical Crossover in Landau$-$Zener Tunneling in Dissipative Rydberg Lattices
In this work, we investigate the excitation dynamics of a Rabi-coupled dissipative Rydberg lattice with a time-dependent detuning. The system is analyzed using (i) a Lindblad master equation within a mean-field approximation and (ii) an effective non-Hermitian Hamiltonian framework. While the mean-field approach captures the emergence of an antiferromagnetic order in the Rydberg excitation profile, the non-Hermitian description provides direct insight into the complex energy spectrum and its avoided crossings, which govern the Landau$-$Zener dynamics. We identify a regime in which the sublattice population imbalance vanishes near the avoided crossing, resulting in identical Landau$-$Zener probabilities on the two sublattices. Beyond a critical effective blockade strength there is a dynamical crossover to another regime in which the sublattice population imbalance persists through the avoided crossing, giving rise to sublattice-dependent Landau$-$Zener probabilities. Furthermore, Rydberg interactions prolong the lifetime of Landau$-$Zener-induced excitations in the presence of weak dissipation and strong Rabi coupling. In contrast, for weak Rabi coupling, the Rydberg blockade inhibits excitation and suppresses the Landau$-$Zener transition probability.
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Quantum Gases · Cross-listed from cond-mat.mes-hall
Topological states of generalized dissipative Majorana wires
We study the generalized one-dimensional (1D) quantum dissipative models corresponding to a Majorana wire which can possess more than one Majorana bound state at each end. The system consists of a 1D fermionic open quantum system whose dynamics is governed by a quadratic Lindblad equation. Using the adjoint Lindblad equation for the fermionic two-point correlations, we find the gaps in the damping and purity spectra of a generic 1D model. Then, using the symmetry-based classification, we show that a winding number as the topological invariant can be defined which distinguishes different steady states of the system in the presence of damping and purity gaps. Then we focus on certain models with different Lindblad quantum jump terms and explore their phase diagrams by calculating the damping and the purity gaps as well as the winding number. In particular, we show that by inclusion of quantum jumps between next-nearest-neighbor sites, higher winding numbers and, equivalently, more Majorana bound states can be achieved. Also, by introducing imbalanced couplings, we can switch between states with negative and positive winding numbers. Finally, we should mention that since our formulation is based on the fermionic correlations rather than the Majorana operators, it can be easily extended to the dissipative topological phases belonging to other symmetry classes.
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Quantum Gases
Tunable Memory Effect in Dissipative Strongly Correlated Quantum Systems
Strongly interacting quantum many-body systems subjected to non-Markovian dissipation pose a formidable challenge due to the interplay between strong correlation effects and memory effects. In this Letter, we develop a general theoretical framework to compute how a system observable responds to dissipation, which captures memory effects at short times and recovers the Markovian limit at longer times. Using this framework, we predict that, for a strongly correlated quantum critical state with critical exponent $\eta$, the short-time dynamics of a system observable always obeys a $t^{2\eta}$ scaling law. This emerges as a universal result from the interplay between strong correlation and memory effects, independent of the microscopic Hamiltonian of the system. We further reveal a crossover behavior of this scaling law to either $t^{2\eta-1}$ or linear-in-$t$ behavior beyond the memory time scale. We propose a concrete physical realization of a non-Markovian bath with tunable memory time using ultracold atoms, where our predictions can be straightforwardly verified in current experiments.
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Monday 10 August
Quantum Gases
Ripple Signatures of Majorana Hybridization across a Topological Quantum Quench
The crossover between topology and nonequilibrium dynamics has emerged as a rich frontier, in which quantum systems can exhibit unique dynamical phenomena that lie beyond the reach of equilibrium. Of particular interest are quench dynamics across topological phase, as it may reveal the information about the underlying Majorana zero-energy states. Here, we investigate the fate of Majorana boundary modes in a quenched fermionic superfluid using self-consistent time-dependent Bogoliubov-de Gennes theory. For quantum quenches within the topological regime, Majorana boundary modes survive but undergo coherent boundary oscillations arising from the nonadiabatic deformation of their wave functions. Furthermore, a pronounced ripple pattern appears in the post-quench density distribution following a sudden topology-changing quench. Here we identify that these ripple structures originates from the coherent hybridization and interference of the initially separated Majorana boundary states. Our findings establish nonequilibrium boundary dynamics as a new approach for probing Majorana physics, which is complementary to conventional equilibrium measurements.
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Quantum Gases · Cross-listed from quant-ph
A Quantum Coherence Microscope in the Hubbard Regime
Quantum coherence underlies collective quantum phenomena and emerging quantum technologies. Quantum gas microscopes have transformed quantum simulation by providing projective snapshots of many-body states with single-atom resolution, but spatially resolved measurements of off-diagonal correlations have remained elusive. Here, using the Talbot effect, we introduce a quantum coherence microscope that maps off-diagonal correlations onto site-resolved density signals with near-single-site resolution. We use this technique to locally probe the superfluid-Mott transition in a layer of a three-dimensional optical lattice and to measure coherence beyond nearest neighbors in an engineered potential landscape. By mapping off-diagonal correlations onto density signals through controlled Talbot evolution, this work opens new possibilities for accessing observables beyond the density basis through tailored matter-wave evolution and recapture.
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Quantum Gases
Jaynes–Cummings dynamics of fermionic heteronuclear dimers in the Mott regime
We formulate and exactly solve a model for coherent association and dissociation of fermionic heteronuclear dimers in the deep-lattice Mott regime. Starting from the onsite three-component atom–molecule Hamiltonian, we show how the single-site model maps to the paradigmatic Jaynes–Cummings Hamiltonian from quantum optics. In this mapping, the fermionic molecular/free-atom sector forms an effective two-level system, while the bosonic atomic mode plays the role of the oscillator degree of freedom. We fix the conserved number of fermionic constituent atoms to one but allow an arbitrary conserved number $N$ of bosonic constituent atoms. The accessible doublet is then $|e,N-1\rangle\leftrightarrow|g,N\rangle$, and the coherent conversion coupling is bosonically enhanced to $\chi\sqrt{N}$. Exact analytic expressions are derived for molecular dissociation, atom-pair association, mode populations, and boson–fermion correlation dynamics. The model provides a transparent matter-wave realization of Jaynes–Cummings physics in a heteronuclear Bose–Fermi system and an exactly solvable setting for understanding coherent atom–molecule conversion and bosonic enhancement in lattice systems.
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Quantum Gases · Cross-listed from quant-ph
Universal entropic occupation statistics in disordered bosonic resonators
Programmable microcavities support grand-canonical photon gases. We show that bosonic state counting creates an entropic staircase of most-probable total occupations. For detuning density continuous and nonzero at the chemical-potential threshold, the active-cell fraction is asymptotically linear at low temperature and the conditional law has a universal limit; for uniform disorder the law is exact over a finite temperature interval. For two modes it is the Gauss–Kuzmin distribution, linking photonic thermodynamics and metric number theory. We outline finite-array and dye-microcavity tests.
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Sunday 9 August
Quantum Gases · Cross-listed from cond-mat.mes-hall
Layer-Locked Chiral Topological Superconductivity
We uncover a universal mechanism for realizing layer-locked topological phases. Guided by it, we investigate the realization of layer-locked chiral topological superconductivity-the superconducting analogue of the quantum anomalous layer Hall effect-in a nonsymmorphic bilayer antiferromagnetic system with s-wave pairing. We identify three distinct gate-tunable topological phases and establish a direct correspondence between the nearly quantized layer-resolved Chern numbers and the layer-locking behavior of chiral Majorana edge states, vortex-core Majorana zero modes, and nearly quantized thermal Hall responses.
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Quantum Gases
Ground-state phase diagram and route to supersolidity in a two-component extended Bose-Hubbard model
We investigate the ground-state phase diagram of a two-component extended Bose-Hubbard model recently realized with dipolar excitons, using the projected entangled-pair states. For the experimentally relevant parameter regime, checkerboard, Mott-insulating, superfluid, and vacuum phases are identified. These phases exhibit orbital-selective character, wherein the two components occupy different quantum states, but we find no evidence for a supersolid phase. The absence of supersolidity is attributed to the strongly interaction-dominated microscopic energy scales, which severely restrict the superfluid regime. Guided by the supersolid mechanism, we further explore a nearby parameter regime with enhanced hopping of one component and identify an orbital-selective supersolid phase. Further finite bond-dimension and unit-cell analyses establish the robustness of this phase. Our results clarify the zero-temperature phase structure of the dipolar-exciton platform and provide a possible route toward realizing supersolidity in this setting.
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Saturday 8 August
Quantum Gases · Cross-listed from cond-mat.stat-mech
Out-of-equilibrium inhomogeneous XX chains: Exact results and the hydrodynamic limit
We study the out-of-equilibrium dynamics in the XX chain with step-like magnetic field, which maps to an inhomogeneous tight-binding chain after Jordan-Wigner transformation. We obtain exact analytic expressions for the fermionic two-point correlation function after a quantum quench from several initial product states, both homogeneous and inhomogeneous ones. This is achieved by using a combination of Fourier and Laplace transforms, which al low us to map the problem to a standard Riemann-Hilbert problem on the unit circle. For arbitrary positions and times the correlators are not expressed in terms of elementary functions. However, in the hydrodynamic limit $x,y,t\to\infty$ with fixed ratios, we provide explicit formulas that depend only on the effective transmission coefficient across the origin. We benchmark our analytic predictions against exact numerical simulations and find excellent agreement in the hydrodynamic limit, apart from finite-time corrections.
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Quantum Gases · Cross-listed from cond-mat.str-el
Fermionic Lattice Supersolidity in the Attractive Three-Color Fermi-Hubbard Model
The recent experimental realization of the half-filled three-color Fermi-Hubbard model on a square optical lattice provides a novel platform for exploring exotic states of matter beyond conventional SU(2) systems. In this Letter, we investigate the three-color Fermi-Hubbard model with color-dependent attractive interactions using determinant quantum Monte Carlo simulations. We find that, at quantum degenerate temperatures, a lattice Fermi supersolid state emerges from the interplay between a moderately-to-strongly interacting two-color subsystem and a weakly coupled third-color environment. This supersolid state, characterized by the coexistence of charge-density-wave and color-superfluid orders, is highly promising for experimental detection with current techniques. Our results demonstrate that the attractive three-color Fermi-Hubbard model on a square optical lattice offers an experimentally accessible system for exploring the supersolidity of ultracold lattice fermions, requiring only a simple lattice geometry and easily tunable onsite interactions.
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Quantum Gases
Fluctuation-based evidence for number–phase dynamics in a frustrated orbital superfluid
Frustrated quantum matter can host intertwined orders rooted in symmetry-related low-energy landscapes, yet static order parameters alone do not reveal how fluctuations are organized among competing configurations. Here we measure mode-resolved shot-to-shot population fluctuations in a $p$-orbital triangular-lattice superfluid with a tunable bias among three valleys. We observe a bias-tuned evolution from enhanced, anticorrelated fluctuations of two minority valleys toward strong confinement of relative-population fluctuations in a selected two-valley stripe phase. The dominant fluctuation structure is captured by an effective canonical model that includes interactions among the condensed modes, supporting a quasi-equilibrium description of the coherent three-valley condensate. Together, the data and model reveal a quantum–thermal regime shaped by pair-tunneling-induced number–phase dynamics, in which relative-phase scrambling softens effective barriers in the minority-valley regime, while phase rigidity gives rise to macroscopic harmonic confinement in the stripe phase. Our results establish mode-resolved fluctuation measurements as a probe of hidden number–phase back-action in frustrated quantum fluids.
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Quantum Gases
Bose-Einstein condensates with Raman-induced spin-orbit coupling : An overview
Since their first realization more than a decade ago spin-orbit-coupled Bose-Einstein condensates have been the subject of intense theoretical and experimental investigations. Spin-orbit coupling deeply modifies the equilibrium properties of the condensate, giving rise to novel configurations such as a supersolid stripe phase and a phase-separated plane-wave state. At the level of dynamics, both the frequency and the nature of the collective modes are significantly affected by the coupling with the spin degree of freedom. Here we review some of the most relevant advances in the field and provide our perspective on possible future research directions.
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Quantum Gases
Quantum tribology: acceleration-induced Stokes friction and Magnus force in correlated Bose fluids
The Landau criterion, a cornerstone of quantum fluid dynamics, dictates that dissipation is forbidden for uniform motion below a critical velocity. Yet, the fundamental question of how acceleration reshapes the principles of quantum friction has remained open since Landau and Pitaevskii's seminal works. Here, we establish a theoretical framework for the quantum tribology of non-inertial motion, describing a probe particle undergoing composite translation and rotation within a weakly interacting Bose condensate. Using the nonlinear Gross-Pitaevskii equation, we show that centripetal acceleration fundamentally modifies the energy-momentum constraints on elementary excitations. This leads to a finite drag force in the subsonic regime of the probe particle motion, and a characteristic quantum stick-slip behaviour in the deeply supersonic regime – a direct generalization of the classical Landau-Pitaevskii picture. Beyond this dissipative response, we uncover a fundamentally distinct mechanism: the nonlinearity of the quantum fluid, combined with the broken symmetry of the trajectory, gives rise to a non-dissipative anomalous transverse force. This quantum Magnus-like response, emerging from the second-order density perturbation, performs no work and is rooted in the geometric asymmetry of the dynamically induced flow. Our findings lay the foundation for a universal program in quantum tribology of accelerated motion, establishing a direct and experimentally testable connection among non-inertial dynamics, nonlinear response, and topological symmetry breaking across platforms ranging from ultracold atoms and exciton-polariton condensates to cosmological analog systems.
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Quantum Gases
Coherent Control of Domain-Wall Transport in an Ultracold Bose Gas
Domain walls are carriers of spin transport whose controlled manipulation underlies a wide range of spintronic and information-processing technologies. Here we demonstrate tunable domain-wall transport in a weakly interacting nondegenerate ultracold Bose gas. We initialize a three-domain pseudo-spin-1/2 texture and observe spontaneous propagation of long-lived domain walls driven by exchange-mediated spin currents. By varying the orientation of the spin domains, we control the balance of spin currents across the walls and thereby tune their trajectories, including reversals of the initial direction of motion. Measurements reveal a crossover from an exchange-stabilized regime, in which coherent spin-exchange collisions suppress wall motion, to a diffusion-dominated regime characterized by rapid transport at thermal velocities. Numerical solutions of a quantum Boltzmann equation reproduce the observed dynamics and identify transverse phase gradients as an important control parameter governing domain-wall propagation. These results establish coherence and phase engineering as tools for programming spin transport in ultracold gases and provide a route toward controllable domain-wall dynamics in atomtronic systems.
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Friday 7 August
Quantum Gases
Phase-Noise-Induced Heating in Optical Lattices
We experimentally and theoretically study the origin of heating in optical lattices by disentangling the respective roles of intensity and phase noise depending on the lattice parameters. While intensity noise is widely identified as a major limiting factor, we show that phase noise can become the dominant heating source, especially for light atoms and deep optical lattices. We provide a simple theoretical framework to predict the phase-noise-induced heating from the power spectral density of the laser phase noise, which can be measured experimentally. We show that such predictions can accurately reproduce the measured heating rates of lithium-6 atoms in a triangular lattice. Our approach is readily generalized to other lattice geometries and atomic species.
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Quantum Gases
Crossing over universal scaling laws in two-dimensional driven dissipative condensates
In low dimensional systems, fluctuations are enhanced and prevent the spontaneous breaking of continuous symmetries. As a result, spatial and temporal correlation functions decay at large distances and long times. A well established example is given by two-dimensional bosonic condensates at equilibrium, which do not display long-range order of the coherence but algebraic decay belonging to the Berezinski-Kosterlitz-Thouless universality class. In contrast, the universal behaviors of non-equilibrium bosonic condensates are more diverse and many open questions remain. Here, we explore the spatio-temporal coherence properties of two-dimensional driven-dissipative polariton condensates in semiconductor optical microcavities. By tuning microscopic parameters, we observe a cross-over between two scaling laws that we attribute to the Edwards-Wilkinson (EW) and the Kardar-Parisi-Zhang (KPZ) universality classes. We demonstrate the collapse of the measured first-order correlations onto the EW and KPZ universal scaling functions and obtain critical exponents, well matching the values predicted theoretically. Our results highlight the intrinsic non-equilibrium nature of polariton condensates and establish them as a platform of choice for controlled exploration of the two-dimensional KPZ universality class.
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Quantum Gases
Observation of far-from-equilibrium scaling in the transient dynamics of 2D quantum magnets
The transient regime of far-from-equilibrium quantum many-body dynamics lacks the established organizing principles that universality and scaling provide in equilibrium. It is least understood for two-dimensional short-range interacting systems, where mean-field arguments are not expected to hold, controlled theoretical descriptions are few, and fluctuations are strong. Here we investigate the quench dynamics of the transverse-field Ising model using programmable Rydberg-atom arrays realizing honeycomb, square, kagome, and triangular lattices. Starting from a fully magnetized state, we observe a pronounced softening of the dominant collective magnetization oscillation accompanied by a maximum in the damping rate, signaling a crossover between interaction- and field-dominated transient dynamics. Even though the microscopic lattice geometries are different, both the oscillation frequencies and the damping rates collapse onto common curves after being rescaled by the coordination-number-weighted interaction strength. Our findings show that a mean-field description effectively reproduces the magnetization oscillations. The importance of correlated quantum fluctuations is underlined by the failure of the discrete truncated Wigner approximation to predict the damping for strong interactions, while tree-tensor-network simulations reproduce the dynamics accurately. These results reveal a robust scaling regime governing the transient dynamics of short-range interacting two-dimensional quantum magnets. They reveal that the dominant transient dynamics is governed by a simple collective description despite the presence of strong quantum fluctuations — an important insight in the quest to uncover organizing principles in far-from-equilibrium quantum matter.
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Quantum Gases · Cross-listed from physics.atom-ph
An ionic clock qubit inside a circular Rydberg atom
Neutral atoms trapped in optical tweezers and excited to Rydberg states, together with trapped ions, are among the most advanced platforms for quantum simulation and quantum computing. Current experiments often rely on additional atoms in neighboring traps to encode ancilla qubits for local manipulation and readout. Here, we demonstrate a dual ion-Rydberg system comprising two qubits encoded in two individually controlled electrons of the same alkaline-earth atom. The first, a microwave qubit, is encoded in a pair of circular Rydberg states, while the second, an optical qubit, is encoded on a narrow quadrupole transition of the Rydberg atom's ionic core. We demonstrate coherent control of the optical qubit and achieve coherence times of several hundred microseconds under dynamical decoupling. Furthermore, we realize coherent coupling between the two electrons via electrostatic quadrupole interactions over the large separation between the Rydberg electron and the ionic core, and map out its angular tunability. Finally, we demonstrate a two-qubit operation, reminiscent of a Mølmer-Sørensen gate, that evolves through an entangled state of the two qubits driven by the quadrupole coupling. Our work opens a pathway to exploit a pair of individually controlled electronic qubits with tunable coupling for quantum simulation and quantum metrology.
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Quantum Gases
Extracting the pairing gap from van Hove singularities in rf spectra of the Fermi Hubbard model
We show that van Hove singularities in rf spectra of the 3D attractive Fermi Hubbard model provide a robust route to extracting the pairing gap. Four types of singularities are classified, and their spectral positions are shown to depend solely on the pairing gap $\Delta$ and chemical potential $\mu$ through simple algebraic relations. Measuring two well-resolved singularities therefore determines both parameters without requiring full spectral fitting. Numerical simulations incorporating phenomenological lifetime and scattering broadenings confirm that these features remain visible in both momentum-integrated and $k_z$-integrated spectra, and become more pronounced at stronger coupling where conventional back-bending methods lose sensitivity. At half filling, particle-hole symmetry fixes $\mu$, reducing the extraction to a single singularity measurement. These results establish vHS analysis as a practical spectroscopic diagnostic for pairing in quantum-simulated 3D Fermi Hubbard systems.
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Quantum Gases
Acoustic fluctuations of two-dimensional dipolar supersolids
We investigate the microscopic structure of the long-wavelength acoustic excitations of two-dimensional dipolar supersolids with triangular and honeycomb crystal order. Using Bogoliubov–de Gennes calculations, we determine the density, phase, current, and lattice-displacement fluctuations associated with the three acoustic modes. We develop a procedure to extract the lattice displacement directly from the microscopic density perturbation, allowing the modes to be identified as one transverse and two longitudinal branches. The displacement field further separates the density fluctuations into contributions from crystal strain and particle transport relative to the lattice. This reveals that the lower longitudinal mode can have large strain and defect-density fluctuations that substantially cancel in the total density response. We show that the long-wavelength fluctuation amplitudes agree with hydrodynamic theory, which is specified entirely by the elastic coefficients of the supersolid. Our analysis provides a microscopic connection between Bogoliubov excitations and the crystalline and superfluid degrees of freedom of two-dimensional supersolids, and identifies their signatures in density- and current-sensitive probes.
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Thursday 6 August
Quantum Gases
Density instabilities and thermal stabilization of phase separated states in dipolar lattice bosons
Recent advances in realizing nearly degenerate dipolar gases in optical lattices have enabled the study of quantum systems with long-range anisotropic interactions. Here, we investigate hard-core dipolar bosons on a two-dimensional square lattice described by an extended Bose–Hubbard model. Using path-integral quantum Monte Carlo simulations at fixed azimuthal angle $\varphi=45^\circ$, we investigate density instabilities arising from first-order phase transitions. We start by mapping the ground-state phase diagram at half filling as a function of dipolar interaction strength and polar angle $\theta$. For weak interactions, the system remains superfluid for all $\theta$. Above a critical interaction strength, the superfluid phase becomes unstable and gives way to checkerboard, stripe, or incompressible phases depending on $\theta$. For $\theta\gtrsim 62^\circ$, we find that half filling becomes unstable and only the empty state, $n=0$, and the fully filled state, $n=1$, are stable. Unlike recent experimental reports of a self-bound insulator at half filling, the homogeneous ground state does not support such a phase, but instead exhibits a direct first-order transition between $n=0$ and $n=1$. At finite temperature, thermal fluctuations shift the onset of density instabilities to larger $\theta$ and stabilize intermediate fillings in the regime where half filling is unstable in the ground state. This leads to phase-separated states consisting of empty and fully filled regions that resemble the experimentally observed "self-bound insulator." In a harmonic trap, similar structures also emerge from phase coexistence associated with the underlying first-order transition.
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Quantum Gases · Cross-listed from cond-mat.mes-hall
Anyon-Impurity Bound States in Quantum-Engineered Fractional Chern Insulators
Mobile impurities provide a powerful means of probing correlated and topological quantum matter, through their dressing by the surrounding medium and the practical probes granting access to the resulting composite object. Motivated by the recent observation of anyon-impurity composites in the solid state, as well as recent realizations of Laughlin-type states in engineered lattice systems, we investigate the formation of a bound state between a mobile impurity and a single pinned quasihole in the interacting Harper-Hofstadter model deep in the fractional Chern insulator regime. Combining analytical arguments with large-scale numerical simulations, we characterize the structure, energetics, and stability of hybrid anyon-impurity bound states, and show that their binding energy provides direct access to the fractional charge of the quasihole under conditions that we identify. We further demonstrate that the composite object can be coherently transported by externally steering the quasihole pinning potential. Our results establish a realistic pathway for controlled anyon-impurity manipulation in quantum-engineered platforms, enabling experimentally feasible protocols for braiding.
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Quantum Gases
Quantum transport in a non-Hermitian 1D synthetic lattice: from quantum Zeno reflection to near-perfect absorption
We experimentally explore the absorption of a propagating wavepacket impinging upon a dissipative region in an engineered quantum system. We employ a 1D non-Hermitian synthetic lattice with an abrupt interface between dissipative and non-dissipative subchains, using the states of the electronic ground-state hyperfine manifold in a $^{87}$Rb Bose-Einstein condensate as sites. By tuning the dissipation rate, we observe a progression from ballistic propagation, to near-perfect absorption, to quantum Zeno reflection. Guided by numerical simulations, we identify that optimal absorption occurs when tunneling and dissipation are properly matched, and find qualitative agreement with an idealized semi-infinite model across all dissipation regimes. Our results establish synthetic lattices as a versatile Quantum simulation platform for dissipation-engineered quantum transport and highlight controlled dissipation as a resource for tailoring quantum dynamics.
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Quantum Gases
Criteria for Feasible Monte Carlo Stochastic Simulations of Bosonic Markovian Open Quantum Dynamics
The Monte Carlo sampling of the stochastic differential equations (SDEs) based on the quasiprobability distribution function, such as the Glauber–Sudarshan P, Wigner, and Husimi Q functions provides a powerful framework for investigating bosonic open quantum many-body dynamics described by the Gorini–Kossakowski–Sudarshan–Lindblad (GKSL) equation, while considering the effects of quantum fluctuations beyond the mean-field approximation. However, the stochastic Monte Carlo simulation is possible only when the corresponding Fokker–Planck equation has a positive-semidefinite diffusion matrix, and the general conditions for the diffusion matrix to be positive semidefinite have remained unclear. In this work, starting from the path integral formulation, we first derive the sufficient conditions under which the diffusion matrix is positive semidefinite for an arbitrary Hamiltonian, jump operators, and choice of quasiprobability distribution functions. We also analytically derive the corresponding SDEs to be solved. We then investigate the dynamics of the GKSL equation in the thermodynamic limit and show that, depending on the form of the jump operators, the mean-field approximation may fail to describe the dynamics accurately, making stochastic Monte Carlo simulations indispensable. Furthermore, we derive the sufficient conditions under which the higher-order quantum fluctuation terms beyond the Fokker–Planck description vanish identically, even when the jump operators contain quadratic terms. Under these conditions, whenever the corresponding SDEs can be derived, the stochastic Monte Carlo simulation reproduces the exact dynamics. These results clarify the conditions under which the stochastic Monte Carlo simulations are both feasible and necessary for accurately describing the dynamics governed by the GKSL equation in phase space.