arXiv subjects

Andrew J. Groszek

Publications and source records attributed to Andrew J. Groszek.

17 recordsLinked to original sources

arXiv2026

Enhanced squeezing for quantum gravimetry in a Bose-Einstein condensate with focussing

Free-fall atom interferometers offer a powerful platform for accurate, absolute gravitational sensing. Szigeti et al. [Phys. Rev. Lett. 125, 100402 (2020)] recently proposed a quantum-enhanced scheme that uses a spin-squeezed Bose-Einstein condensate as an input state to improve the phase sensitivity of the interferometer. The spin squeezing, generated via one-axis twisting interactions, was limited by condensate expansion. Here we present an improved state preparation in which a sudden trapping potential -- a delta kick -- is initially applied to focus the condensate. The resulting increase in density enhances the one-axis-twisting interactions and produces greater spin squeezing. Using multimode truncated-Wigner simulations, we quantify the performance of the interferometer and find that, for an optimal kick strength, the phase sensitivity surpasses the standard quantum limit by a factor of $\sim 20$. This represents a fourfold improvement over the original scheme without the delta kick and is well captured by a two-mode approximation.

cond-mat.quant-gas↗

arXiv2026

Universal coarsening of a two-dimensional Bose gas under conservative evolution

We investigate the phase ordering dynamics of a uniform two-dimensional Bose gas quenched to a finite temperature in the superfluid phase. Starting from a defect-rich, far-from-equilibrium state, we model the subsequent evolution with the projected Gross-Pitaevskii equation, which conserves both energy and particle number. By tuning the initial energy, we control the effective post-quench temperature and examine its role in the equilibration dynamics. We find that the gas exhibits universal behaviour at all temperatures, evidenced by spatio-temporal scaling of correlation functions and power-law growth of the correlation length $\sim t^{1/z}$, with $z$ the dynamical critical exponent. We find $z$ to be temperature dependent, with $z \approx 1.5$ for post-quench temperatures just below the Berezinskii-Kosterlitz-Thouless (BKT) transition, and $z \approx 1.9$ for quenches to near-zero temperature. Analysis of the Porod tail of the momentum distribution suggests a temperature-dependent competition between vortices and sound waves in the coarsening process. The two-time correlation function also exhibits universal scaling, decaying as $\sim t^{-λ/z}$, with autocorrelation exponent $λ$. Near the BKT transition we obtain $λ\approx 2$, whereas $λ$ is found to diverge as the effective temperature approaches zero.

cond-mat.quant-gas↗

arXiv2025

Unblockable Communication With Gravity

All modern wireless communication technologies are based on electromagnetism. However, electromagnetic signals are susceptible to screening and blocking, so their availability cannot be guaranteed in adverse environments. This raises a fundamental question: Can information be transmitted through a truly unblockable channel? Here we show that gravity, unlike electromagnetism, offers such a path. We propose and implement a wireless communication protocol in which a broadcaster encodes a binary message by moving a mass, while a receiver detects the resulting gravitational signal with a gravimeter. We validate this scheme experimentally, successfully transmitting a gravitational message a distance of $\approx$ 0.7 m through a brick wall at a rate of 1 bit min$^{-1}$. These results establish gravity as a viable platform for unblockable communication.

physics.gen-ph↗

arXiv2024

Berezinskii-Kosterlitz-Thouless transitions in a ferromagnetic superfluid: effects of axial magnetization

An easy-plane ferromagnetic spin-1 Bose gas undergoes two Berezinskii-Kosterlitz-Thouless (BKT) transitions, associated with mass and spin superfluidity respectively. We study the effect of axial magnetization on the superfluid properties of this system. We find that nonzero axial magnetization couples mass and spin superflow, via a mechanism analogous to the Andreev-Bashkin effect present in two-component superfluids. With sufficiently large axial magnetization mass and spin superfluidity arise simultaneously. The cross-over to this phase provides a finite-temperature generalization of the zero-temperature broken-axisymmetric to easy-axis transition. We present analytic relations connecting mass and spin superfluidity with experimentally observable coherence of the three spinor components and local magnetization.

cond-mat.quant-gas↗

arXiv2023

Fluctuation theorem anomaly in a point-vortex fluid

The second law of thermodynamics posits that in closed macroscopic systems the rate of entropy production must be positive. However, small systems can exhibit negative entropy production over short timescales, seemingly in contradiction with this law. The fluctuation theorem quantitatively connects these two limits, predicting that entropy producing trajectories become exponentially dominant as the system size and measurement time are increased. Here we explore the predictions of the fluctuation theorem for a fluid of point-vortices, where the long-range interactions and existence of negative absolute temperature states provide an intriguing test bed for the theorem. Our results suggest that while the theorem broadly holds even at negative absolute temperatures, the long-range interactions inherent to the vortex matter lead to anomalously large entropy production over short time intervals. The predictions of the fluctuation theorem are only fully recovered when sufficient noise is introduced to the dynamics to overwhelm the vortex-vortex interactions.

cond-mat.quant-gas↗

arXiv2023

Viability of rotation sensing using phonon interferometry in Bose-Einstein condensates

We demonstrate the use of a ring-shaped Bose-Einstein condensate as a rotation sensor by measuring the interference between two counter-propagating phonon modes imprinted azimuthally around the ring. We observe rapid decay of the excitations, quantified by quality factors of at most $Q \approx 27$. We numerically model our experiment using the c-field methodology, allowing us to estimate the parameters that maximise the performance of our sensor. We explore the damping mechanisms underlying the observed phonon decay, and identify two distinct Landau scattering processes that each dominate at different driving amplitudes and temperatures. Our simulations reveal that $Q$ is limited by strong damping of phonons even in the zero temperature limit. We perform an experimental proof-of-principle rotation measurement using persistent currents imprinted around the ring. We demonstrate a rotation sensitivity of up to $ΔΩ\approx 0.3$ rad/s from a single image, with a theoretically achievable value of $ΔΩ\approx 0.04$ rad/s in the atomic shot-noise limit. This is a significant improvement over the shot-noise-limited $ΔΩ\approx 1$ rad/s sensitivity obtained by Marti et al. [Phys. Rev. A 91, 013602 (2015)] for a similar setup.

cond-mat.quant-gas↗

arXiv2023

Berezinskii-Kosterlitz-Thouless transitions in an easy-plane ferromagnetic superfluid

A two-dimensional (2D) spin-1 Bose gas exhibits two Berezenskii-Kosterlitz-Thouless (BKT) transitions in the easy-plane ferromagnetic phase. The higher temperature transition is associated with superfluidity of the mass current determined predominantly by a single spin component. The lower temperature transition is associated with superfluidity of the axial spin current, quasi-long range order of the transverse spin density and binding of polar-core spin vortices (PCVs). Above the spin BKT temperature, the component circulations that make up each PCV spatially separate, suggesting possible deconfinement analogous to quark deconfinement in high energy physics. Intercomponent interactions give rise to superfluid drag between the spin components, which we calculate analytically at zero temperature. We present the mass/spin superfluid phase diagram as a function of quadratic Zeeman energy $q$. At $q=0$ the system is in an isotropic spin phase with $\mathrm{SO}(3)$ symmetry. Here the fluid response exhibits a system size dependence, suggesting the absence of a BKT transition. Despite this, for finite systems the decay of spin correlations changes from exponential to algebraic as the temperature is decreased.

cond-mat.quant-gas↗

arXiv2021

Simulating cosmological supercooling with a cold atom system II

We perform an analysis of the supercooled state in an analogue of an early universe phase transition based on a one dimensional, two-component Bose gas with time-dependent interactions. We demonstrate that the system behaves in the same way as a thermal, relativistic Bose gas undergoing a first order phase transition. We propose a way to prepare the state of the system in the metastable phase as an analogue to supercooling in the early universe. While we show that parametric resonances in the system can be suppressed by thermal damping, we find that the theoretically estimated thermal damping in our model is too weak to suppress the resonances for realistic experimental parameters. However, we propose that experiments to investigate the effective damping rate in experiments would be worthwhile.

cond-mat.quant-gas↗

arXiv2021

Crossover in the dynamical critical exponent of a quenched two-dimensional Bose gas

We study the phase ordering dynamics of a uniform Bose gas in two dimensions following a quench into the ordered phase. We explore the crossover between dissipative and conservative evolution by performing numerical simulations within the classical field methodology. Regardless of the dissipation strength, we find clear evidence for universal scaling, with dynamical critical exponent $z$ characterising the growth of the correlation length. In the dissipative limit we find growth consistent with the logarithmically corrected law $[t/\log(t/t_0)]^{1/z}$, and exponent $z=2$, in agreement with previous studies. Decreasing the dissipation towards the conservative limit, we find strong numerical evidence for the expected growth law $t^{1/z}$. However, we observe a smooth crossover in $z$ that converges to an anomalous value distinctly lower than $2$ at a small finite dissipation strength. We show that this lower exponent may be attributable to a power-law vortex mobility arising from vortex--sound interactions.

cond-mat.quant-gas↗

arXiv2021

Geometric phases of a vortex in a superfluid

We consider geometric phases of mobile quantum vortices in superfluid Bose-Einstein condensates. Haldane and Wu [Phys. Rev. Lett. 55, 2887 (1985)] showed that the geometric phase, $γ_{\mathcal C}=2πN_{\mathcal C}$, of such a vortex is determined by the number of condensate atoms $N_{\mathcal C}$ enclosed by the vortex trajectory. Considering an experimentally realistic freely orbiting vortex leads to an apparent disagreement with this prediction. We resolve it using the superfluid electrodynamics picture, which allows us to identify two additional contributions to the measured geometric phase; (i) a topologically protected edge current of vortices at the condensate boundary, and (ii) a superfluid displacement current. Our results generalise to, and pave the way for experimental measurements of vortex geometric phases using scalar and spinor Bose--Einstein condensates, and superfluid Fermi gases.

cond-mat.quant-gas↗

arXiv2020

Decaying quantum turbulence in a two-dimensional Bose-Einstein condensate at finite temperature

We numerically model decaying quantum turbulence in two-dimensional disk-shaped Bose-Einstein condensates, and investigate the effects of finite temperature on the turbulent dynamics. We prepare initial states with a range of condensate temperatures, and imprint equal numbers of vortices and antivortices at randomly chosen positions throughout the fluid. The initial states are then subjected to unitary time-evolution within the c-field methodology. For the lowest condensate temperatures, the results of the zero temperature Gross-Pitaevskii theory are reproduced, whereby vortex evaporative heating leads to the formation of Onsager vortex clusters characterised by a negative absolute vortex temperature. At higher condensate temperatures the dissipative effects due to vortex-phonon interactions tend to drive the vortex gas towards positive vortex temperatures dominated by the presence of vortex dipoles. We associate these two behaviours with the system evolving toward an anomalous non-thermal fixed point, or a Gaussian thermal fixed point, respectively.

cond-mat.quant-gas↗

arXiv2018

Order from chaos: Observation of large-scale flow from turbulence in a two-dimensional superfluid

Interacting systems driven far from equilibrium tend to evolve to steady states exhibiting large-scale structure and order. In two-dimensional turbulent flow the seemingly random swirling motion of a fluid can evolve towards persistent large-scale vortices. Lars Onsager proposed a model based on statistical mechanics of quantized vortices to explain such behavior. Here we report the first experimental confirmation of Onsager's model of turbulence. We drag a grid barrier through an oblate superfluid Bose--Einstein condensate to generate non-equilibrium distributions of vortices. We observe an inverse energy cascade driven by the evaporative heating of vortices, leading to steady-state configurations characterized by negative temperatures. Our results open a pathway for quantitative studies of emergent structures in interacting quantum systems driven far from equilibrium.

cond-mat.quant-gas↗

arXiv2018

Motion of vortices in inhomogeneous Bose-Einstein condensates

We derive a general and exact equation of motion for a quantised vortex in an inhomogeneous two-dimensional Bose-Einstein condensate. This equation expresses the velocity of a vortex as a sum of local ambient density and phase gradients in the vicinity of the vortex. We perform Gross-Pitaevskii simulations of single vortex dynamics in both harmonic and hard-walled disk-shaped traps, and find excellent agreement in both cases with our analytical prediction. The simulations reveal that, in a harmonic trap, the main contribution to the vortex velocity is an induced ambient phase gradient, a finding that contradicts the commonly quoted result that the local density gradient is the only relevant effect in this scenario. We use our analytical vortex velocity formula to derive a point-vortex model that accounts for both density and phase contributions to the vortex velocity, suitable for use in inhomogeneous condensates. Although good agreement is obtained between Gross-Pitaevskii and point-vortex simulations for specific few-vortex configurations, the effects of nonuniform condensate density are in general highly nontrivial, and are thus difficult to efficiently and accurately model using a simplified point-vortex description.

cond-mat.quant-gas↗

arXiv2018

Einstein-Bose condensation of Onsager vortices

We have studied statistical mechanics of a gas of vortices in two dimensions. We introduce a new observable---a condensate fraction of Onsager vortices---to quantify the emergence of the vortex condensate. The condensation of Onsager vortices is most transparently observed in a single vortex species system and occurs due to a competition between solid body rotation (c.f. vortex lattice) and potential flow (c.f. multiple quantum vortex state). We propose an experiment to observe the condensation transition of the vortices in such a single vortex species system.

cond-mat.quant-gas↗

arXiv2018

Vortex Thermometry for Turbulent Two-Dimensional Fluids

We introduce a new method of statistical analysis to characterise the dynamics of turbulent fluids in two dimensions. We establish that, in equilibrium, the vortex distributions can be uniquely connected to the temperature of the vortex gas, and apply this vortex thermometry to characterise simulations of decaying superfluid turbulence. We confirm the hypothesis of vortex evaporative heating leading to Onsager vortices proposed in Phys. Rev. Lett. 113, 165302 (2014), and find previously unidentified vortex power-law distributions that emerge from the dynamics.

cond-mat.quant-gas↗

arXiv2016

Onsager vortex formation in Bose-Einstein condensates in two-dimensional power-law traps

We study computationally dynamics of quantised vortices in two-dimensional superfluid Bose-Einstein condensates confined in highly oblate power-law traps. We have found that the formation of large scale Onsager vortex clusters prevalent in steep-walled traps is suppressed in condensates confined by harmonic potentials. However, the shape of the trapping potential does not appear to adversely affect the evaporative heating efficiency of the vortex gas. Instead, the suppression of Onsager vortex formation in harmonic traps can be understood in terms of the energy of the vortex configurations. Furthermore, we find that the vortex-antivortex pair annihilation that underpins the vortex evaporative heating mechanism requires the interaction of at least three vortices. We conclude that experimental observation of Onsager vortices should be the most apparent in flat or inverted-bottom traps.

cond-mat.quant-gas↗

arXiv2016

Hamiltonian dynamics of two same-sign point vortices

We have studied numerically the Hamiltonian dynamics of two same-sign point vortices in an effectively two-dimensional, harmonically trapped Bose-Einstein condensate. We have found in the phase space of the system an impenetrable wall that divides the dynamics into two distinct and exhaustive types. In the two-dimensional position-coordinate space, the first type corresponds to intersecting single-vortex orbits and the second type to orbits that have no points in common. The two types are also easily distinguished in the two-dimensional space spanned by the radial and angular velocities of the vortices: in the first type, both single-vortex orbits are the same simple loop in this two-dimensional space, whereas in the second type the two orbits constitute two nonintersecting loops. The phase-space-dividing wall is distinct from the bifurcation curve of rigidly rotating states found by Navarro et al. [Phys. Rev. Lett. 110, 225301 (2013)].

cond-mat.quant-gas↗