Atomtronic quantum sensors based on trapped superfluids offer a promising platform for high-precision inertial measurements where the dynamics of quantized vortices can serve as sensitive probes of external forces. We analytically investigate the persistent current oscillations between two density-coupled Bose-Einstein condensate rings of equal radius and show that the vortex dynamics is governed by low-energy acoustic excitations circulating through the condensate bulk. The oscillation frequency and damping rate are quantitatively predicted by a simplified hydrodynamic model, in agreement with Bogoliubov–de Gennes analysis and Gross-Pitaevskii simulations. We identify the critical dissipation separating persistent oscillations from overdamped vortex localization. Furthermore, we demonstrate that periodic modulation of the interring barrier at resonant frequencies enables controlled vortex transfer even when the condensates are well separated in density. These results clarify the role of collective hydrodynamic modes in circulation transfer and establish a framework for employing vortex dynamics in atomtronic quantum technologies.
Atomtronic quantum sensors based on trapped superfluids offer a promising platform for high-precision inertial measurements where the dynamics of quantized vortices can serve as sensitive probes of external forces. We analytically investigate the persistent current oscillations between two density-coupled Bose-Einstein condensate rings of equal radius and show that the vortex dynamics is governed by low-energy acoustic excitations circulating through the condensate bulk. The oscillation frequency and damping rate are quantitatively predicted by a simplified hydrodynamic model, in agreement with Bogoliubov–de Gennes analysis and Gross-Pitaevskii simulations. We identify the critical dissipation separating persistent oscillations from overdamped vortex localization. Furthermore, we demonstrate that periodic modulation of the interring barrier at resonant frequencies enables controlled vortex transfer even when the condensates are well separated in density. These results clarify the role of collective hydrodynamic modes in circulation transfer and establish a framework for employing vortex dynamics in atomtronic quantum technologies.
Persistent currents–inviscid quantized flow around an atomic circuit–are a crucial building block of atomtronic devices. We investigate how acceleration influences the transfer of persistent currents between two density-connected, ring-shaped atomic Bose-Einstein condensates, joined by a tunable weak link that controls system topology. We find that the acceleration of this system modifies both the density and phase dynamics between the rings, leading to a bias in the periodic vortex oscillations studied in T. Bland et al., Phys. Rev. Research 4, 043171 (2022). Accounting for dissipation suppressing such vortex oscillations, the acceleration facilitates a unilateral vortex transfer to the leading ring. We analyze how this transfer depends on the weak-link amplitude, the initial persistent current configuration, and the acceleration strength and direction. Characterization of the sensitivity to these parameters paves the way for a new platform for acceleration measurements, for which we outline a proof-of-concept ultracold double-ring accelerometer.
In this thesis we solve the Gross-Pitaevskii equation numerically in order to model the response of trapped Bose-Einstein condensed gases to perturbations by electromagnetic fields. First, we simulate output coupling of pulses from the condensate and compare our results to experiments. The excitation and separation of eigenmodes on flow through a constriction is also studied. We then move on to the main theme of this thesis: the important subject of quantised vortices in Bose condensates, and the relation between Bose-Einstein condensation and superfluidity. We propose methods of producing vortex pairs and rings by controlled motion of objects. Full three-dimensional simulations under realistic experimental conditions are performed in order to test the validity of these ideas. We link vortex formation to drag forces on the object, which in turn is connected with energy transfer to the condensate. We therefore argue that vortex formation by moving objects is intimately related to the onset of dissipation in superfluids. We discuss this idea in the context of a recent experiment, using simulations to provide evidence of vortex formation in the experimental scenario. Superfluidity is also manifest in the property of persistent currents, which is linked to vortex stability and dynamics. We simulate vortex line and ring motion, and find in both cases precessional motion and thermodynamic instability to dissipation. Strictly speaking, the Gross-Pitaevskii equation is valid only for temperatures far below the BEC transition. We end the thesis by describing a simple finite-temperature model to describe mean-field coupling between condensed and non-condensed components of the gas. We show that our hybrid Monte-Carlo/FFT technique can describe damping of the lowest energy excitations of the system. Extensions to this model and future research directions are discussed in the conclusion. (author)
This work investigates the dynamical stability, parametric excitation, and impurity (tracer) trapping kinetics of quantized vortex filaments in periodically modulated superfluid systems (Bose-Einstein Condensates and Helium-II). Within the framework of the Local Induction Approximation (LIA) and linear perturbation theory, we show that external quadrupole pressure/density modulation couples counter-propagating Kelvin waves, which is modeled via the Rotating Wave Approximation (RWA) as a damped Mathieu-type autonomous system. By employing the microscopic theory of Bogoliubov phonon scattering off a quantized vortex core (Pitaevskii-Fetter theory), we integrate a T⁵ temperature dependence of the mutual friction drag force. Accounting for this thermodynamic damping and the mechanical cavitation limit ε_max ≈ c_s/ξ, we analytically derive the minimum parametric excitation threshold ε_min(T) = C₁ T⁵. For a ⁸⁷Rb condensate, we establish that the stable helical phase is strictly bounded by a critical crossover temperature T_cross ≈ 34 pK, above which the thermal phonon damping demands a driving amplitude that inevitably causes structural cavitation. Furthermore, the kinetics of neutral impurity trapping into the vortex core are evaluated in two distinct regimes. In the viscous (overdamped) Helium-II regime (T ~ 1-1.5 K), we obtain the characteristic trapping time scaling τ_trap ∝ T⁴ R_part⁻¹. In the ballistic (underdamped) BEC regime (34 pK < T ~ 10-50 nK for straight vortices, and T < 34 pK for helical vortices), the trapping is driven by acoustic bremsstrahlung. By evaluating the inertial acceleration of the tracer via orbital force balance, we show that the trapping time scales quadratically with the density ratio, yielding τ_trap(BEC) ∝ (ρ_part / ρ_s)², which is numerically evaluated as ≈ 6.5 s for a density-matched macroscopic tracer. Finally, we estimate the critical trapping velocity to be v_c ≈ 0.1–1 mm/s. Thermodynamic Crossover (T_cross): Establishes that the stable helical vortex phase in a ⁸⁷Rb BEC is strictly bounded by T_cross ≈ 34 pK due to the competition between T⁵ phonon damping and the mechanical cavitation limit. Dual-Regime Impurity Trapping Kinetics: Derives the trapping time scaling laws for both the viscous Helium-II regime (τ_trap ∝ T⁴) and the ballistic BEC regime where capturing is mediated by acoustic bremsstrahlung (τ_trap(BEC) ∝ (ρ_part / ρ_s)²). Experimental Verification: Connects the theoretical boundaries to state-of-the-art microgravity BEC platforms (Cold Atom Lab and QUANTUS) and Feshbach tuning methods.
Precise control of topologically protected excitations, such as quantum vortices in atomtronic circuits, opens new possibilities for future quantum technologies. We theoretically investigate the dynamics of Josephson vortices (rotational fluxons) induced by coupled persistent currents in a system of coplanar double-ring atomic Bose-Einstein condensates. We study the Josephson effect in an atomic Josephson junction formed by coaxial ring-shaped condensates. Tunneling superflows, initiated by an imbalance in atomic populations between the rings, are significantly influenced by the persistent currents in the inner and outer rings. This results in pronounced Josephson oscillations in the population imbalance for both corotating and nonrotating states. If a linear acceleration is applied to the system, our analysis reveals peculiar azimuthal tunneling patterns and dynamics of Josephson vortices which leads to nonzero net tunneling current and shows sensitivity to the acceleration magnitude. When multiple Josephson vortices are present, asymmetric vortex displacements that correlate with both the magnitude and direction of acceleration can be measured, offering the potential for quantum sensing applications.
We investigate Josephson transport in a fully closed, two-dimensional superfluid circuit formed by a ring-shaped Rb 87 Bose-Einstein condensate that contains two optical barriers acting as movable weak links. Translating these barriers at controlled speeds imposes a steady bias current, enabling direct mapping of the current-chemical-potential ( I − Δ μ ) characteristics. For narrow junctions ( w ≈ 1 µ m ), the circuit exhibits a pronounced dc branch that terminates at a critical current I c = 9 ( 1 ) × 10 3 s − 1 ; above this threshold, the system switches to an ac, resistive regime. Classical-field simulations that include the moving barriers quantitatively reproduce both the nonlinear I − Δ μ curve and the measured I c , validating the underlying microscopic picture. Analysis of the ensuing phase dynamics shows that dissipation is mediated by the nucleation and traversal of vortex-antivortex pairs through the junctions, while the bulk condensate remains globally phase locked—direct evidence of the ring's topological constraint enforcing quantized circulation. These results establish a cold-atom analog of a superconducting quantum interference device in which Josephson dynamics can be resolved at the single-vortex level, providing a versatile platform for atomtronic circuit elements, nonreciprocal Josephson devices, and on-chip Sagnac interferometers for multiaxis rotation sensing.
Persistent currents in annular geometries have played an important role in disclosing the quantum phase coherence of superconductors and mesoscopic electronic systems.Ultracold atomic gases in multiply connected traps also exhibit long-lived supercurrents and have attracted much interest both for fundamental studies of superfluid dynamics and as prototypes for atomtronics circuits.Here, we report on the realization of supercurrents in homogeneous, tunable fermionic rings.We gain exquisite, rapid control over quantized persistent currents in all regimes of the BCS-BEC crossover through a universal phase-imprinting technique, attaining on-demand circulations w as high as 9. High-fidelity readout of the superfluid circulation state is achieved by exploiting an interferometric protocol, which also yields local information about the superfluid phase around the ring.In the absence of externally introduced perturbations, we find the induced metastable supercurrents to be as long-lived as the atomic sample.Conversely, we trigger and inspect the supercurrent decay by inserting a single small obstacle within the ring.For circulations higher than a critical value, the quantized current is observed to dissipate via the emission of vortices, i.e., quantized phase slips, which we directly image, in good agreement with numerical simulations.The critical circulation at which the superflow becomes unstable is found to depend starkly on the interaction strength, taking its maximum value for the unitary Fermi gas.Our results demonstrate fast and accurate control of quantized collective excitations in a macroscopic quantum system and establish strongly interacting fermionic superfluids as excellent candidates for atomtronics applications.