Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

C-field description of the quasi-equilibrium Bose gas: Persistent currents and kelvon-induced vortex decay

S. J. Rooney

Published Jan 1, 2012• 0 citations
OpenAlex

Abstract

Recent experiments at the University of Arizona have demonstrated superb control and imaging of flattened superfluids revealing a rich landscape of vortex dynamics. Vortex dipoles have been created and their dynamics observed [Neely et al. Phys. Rev. Lett. 104, 160410 (2010)], and highly charged persistent currents have been formed through a clever combination of stirring and dissipation [T. W. Neely, PhD thesis, (2010)]. Many ultra-cold gas systems, including these, are in a regime that we may characterize as quasi-equilibrium: despite some external forcing, a large fraction of the gas remains in thermal equilibrium. In this thesis we use the stochastic projected Gross-Pitaevskii equation (SPGPE) to make quantitative predictions of the quasi-equilibrium Bose gas. \n\nWe quantitatively compare the SPGPE with experiment by modeling the persistent current formation experiment performed at the University of Arizona [T. W. Neely, PhD thesis, (2010)]. We determine all SPGPE parameters for the toroidal system prior to simulation, enabling quantitative modeling of the experiment with no fitting parameters, giving a true test of the SPGPE theory. We find the SPGPE gives quantitative agreement with experiment, accurately predicting the size of the persistent current as well as the decay time of the vortices. We also observe the crucial role that thermal fluctuations have on enabling this agreement, showing the comprehensive SPGPE treatment is necessary to make quantitatively accurate calculations of quasi-equilibrium systems. This is the first quantitative agreement with experimental observations of vortex dynamics obtained with a theory of dissipation from first principles using no fitting parameters.\n\nWe then systematically study the Kelvin mode excitations on a vortex line in a three dimensional Bose-Einstein condensate using the SPGPE. We give a quantitative measure of the magnitude of vortex bending caused by the activation of Kelvin modes, and find that vortex bending can be suppressed by tightening the confinement along the direction of the vortex line. This leads to a strong suppression of the vortex decay rate as the system enters a regime of two-dimensional vortex dynamics, characterized by a critical oblateness.\n\nIn our final application of the SPGPE we simulate the decay of a vortex dipole. We model a recent experiment of Neely et al. [Neely et al. Phys. Rev. Lett. 104, 160410 (2010)], finding the SPGPE predicts a dipole lifetime consistent with experimental observations. We also show the experiment lies in the two-dimensional regime of vortex dynamics, validating our critical oblateness calculation.

Related papers

Suppression of Kelvon-induced decay of quantized vortices in oblate Bose-Einstein condensates

S. J. Rooney, P. B. Blakie, Brian P. Anderson +1 more

We study the Kelvin mode excitations on a vortex line in a three-dimensional trapped Bose-Einstein condensate at finite temperature. Our stochastic Gross-Pitaevskii simulations show that the activation of these modes can be suppressed by tightening the confinement along the direction of the vortex line, leading to a strong suppression in the vortex decay rate as the system enters a regime of two-dimensional vortex dynamics. As the system approaches the condensation transition temperature, we find that the vortex decay rate is strongly sensitive to dimensionality and temperature, observing a large enhancement for quasi-two-dimensional traps. Three-dimensional simulations of the recent vortex dipole decay experiment of Neely et al. [Phys. Rev. Lett. 104, 160401 (2010)] confirm two-dimensional vortex dynamics and predict a dipole lifetime consistent with experimental observations and suppression of Kelvon-induced vortex decay in highly oblate condensates.

arXiv:1105.1189•Physical Review A•Aug 29, 2011•68 citations

Implementation and Applications of the Stochastic Projected Gross-Pitaevskii Equation

S. J. Rooney

Providing a complete description of dissipative superfluid dynamics is one of the major challenges of many-body quantum field theory. In this thesis we make a fundamental step towards this goal by implementing the stochastic projected Gross-Pitaevskii equation (SPGPE) in complete form for the first time. The SPGPE is a high-temperature theory of Bose-Einstein condensate dynamics, providing a classical-field description of a low-energy subspace in contact with a thermal reservoir. The reservoir interaction terms account for dissipation and noise from thermal interactions, and arise from two distinct processes described as number-damping and energy-damping. This work advances previous applications of the SPGPE theory, which have only included number-damping processes, by implementing the energy-damping processes. We describe the properties of the deterministic and noise terms corresponding to the energy-damping process, and develop a novel algorithm to accurately and efficiently evaluate the energy-damping terms in the SPGPE. We apply the SPGPE to a range of experimentally accessible systems, considering both non-equilibrium and quasi-equilibrium dynamics. We model the experiment of Neely et al. [Phys. Rev. Lett. 111, 235301 (2013)], where stirring of a toroidally trapped Bose-Einstein condensate generates a disordered array of quantum vortices that decay, via thermal dissipation, to form a macroscopic persistent current. We perform numerical simulations of the experiment using the number-damping SPGPE and ab initio determined reservoir parameters. We quantitatively reproduce both the formation time and size of the persistent current, as measured in the experiment. In the first application of the full SPGPE, we consider the non-equilibrium dynamics of a condensate excited into a large-amplitude breathing mode. We find that in such non-equilibrium regimes, the energy-damping dominates over the number-damping process, leading to qualitatively different system dynamics. In particular, energy damping causes the system to rapidly reach thermal equilibrium without greatly depleting the condensate, showing that energy damping provides a highly coherent dissipation mechanism. Finally, we apply the SPGPE to the quasi-equilibrium dynamics of single-vortex decay. Energy-damping processes have previously been neglected for this system. SPGPE simulations show that in fact energy-damping has a dominant effect on the lifetime of a single vortex, with lifetimes less than half those predicted by the number-damping SPGPE. In contrast to the breathing mode decay, we observe little qualitative difference between the energy-damping and number-damping descriptions of vortex decay. Our findings show that while energy-damping processes are important to quantitatively describe quasi-equilibrium dynamics, the system behavior may be described by the number-damping SPGPE with a suitably modified dissipation rate.

•Jan 1, 2015•1 citation

Persistent-current formation in a high-temperature Bose-Einstein condensate: An experimental test for classical-field theory

S. J. Rooney, Tyler W. Neely, Brian P. Anderson +1 more

Experimental stirring of a toroidally trapped Bose-Einstein condensate at high temperature generates a disordered array of quantum vortices that decays via thermal dissipation to form a macroscopic persistent current [T. W. Neely et al., Phys. Rev. Lett. 111, 235301 (2013)]. We perform three-dimensional numerical simulations of the experimental sequence within the stochastic projected Gross-Pitaevskii equation using ab initio determined reservoir parameters. We find that both damping and noise are essential for describing the dynamics of the high-temperature Bose field. The theory gives a quantitative account of the formation of a persistent current, with no fitted parameters.

arXiv:1208.4421•Physical Review A•Dec 11, 2013•40 citations

Decay of a quantum vortex: Test of nonequilibrium theories for warm Bose-Einstein condensates

S. J. Rooney, Ashton S. Bradley, P. B. Blakie

The decay of a vortex from a nonrotating high temperature Bose-Einstein condensate is modeled using the stochastic projected Gross-Pitaevskii equation (SPGPE). In order to exploit the tunability of temperature in SPGPE theory while maintaining the total atom number constant, we develop a simple and accurate Hartree-Fock method to estimate the SPGPE parameters for systems close to thermal equilibrium. We then calculate the lifetime of a vortex using three classical field theories that describe vortex decay in different levels of approximation. The SPGPE theory is shown to give the most complete description of the decay process, predicting significantly shorter vortex lifetimes than the alternative theories. Using the SPGPE theory to simulate vortex decay for a trapped gas of $5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ $^{87}\mathrm{Rb}$ atoms, we calculate a vortex lifetime $\mathrm{t\ifmmode \bar{}\else \={}\fi{}}$ that decreases linearly with temperature, falling in the range $20\mathrm{s}>\mathrm{t\ifmmode \bar{}\else \={}\fi{}}>1.5\mathrm{s}$ corresponding to the temperature range $0.78{T}_{c}\ensuremath{\leqslant}T\ensuremath{\leqslant}0.93{T}_{c}$. The vortex lifetimes calculated provide a lower bound for the lifetime of a persistent current with unit winding number in our chosen trap geometry in the limit of vanishing vortex pinning potential.

arXiv:0912.3300•Physical Review A•Feb 26, 2010•78 citations

Vortices in trapped Bose-Einstein condensates

Brian Jackson

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)

•Jan 1, 2000•1 citation

Ab initio modelling of quasi-one-dimensional Bose gas experiments via the stochastic Gross-Pitaevskii equation

Donatello Gallucci

In this thesis we use the stochastic Gross-Pitaevskii equation (SGPE), a finite temperature model for weakly interacting ultracold Bose gases which fully incorporates density and phase fluctuations, to demonstrate ab initio quantitative agreement with a number of quasi-one-dimensional experiments. To achieve this, we propose and numerically solve a quasi-one-dimensional form of the SGPE, supported by a self-consistent treatment of radially-excited thermal modes. The quasi-one-dimensional stochastic Gross-Pitaevskii equation provides an accurate finite temperature description of the dynamical equilibrium of the lowenergy axial modes of a Bose gas, assumed to be highly populated and thus treated within the ‘classical field’ approximation. This treatment allows to selfconsistently account for transverse, quasi-one-dimensional effects, which makes it a valid model in the regime where the chemical potential, μ, is approximately equal to a few times the transverse excitation energy, ~ω⊥. In the regime where the thermal energy, kBT , is also comparable to or larger than ~ω⊥, the transverse excited states play an increasingly important role, and are treated here as onedimensional independent Bose gases at static equilibrium. Firstly, we demonstrate that this is an excellentmodel for ab initio investigation of equilibrium properties, such as density profiles and density fluctuations. This is shown by accurately reproducing the in situ density profiles recently obtained in the experiments of Trebbia et al. [Phys. Rev. Lett. 97, 250403 (2006)] and van Amerongen et al. [Phys. Rev. Lett. 100, 090402 (2008)], and the density fluctuation data reported by Armijo et al. [Phys. Rev. Lett. 105, 230402 (2010)]. Moreover, we perform an ab initio analysis of the temperature dependence of the phase coherence of finite temperature, quasi-one-dimensional Bose gases measured in the experiments of Richard et al. [Phys. Rev. Lett. 91, 010405 (2003)] and Hugbart et al. [Eur. Phys. J. D 35, 155 (2005)]. We find very good agreement across the entire observed temperature range in both experiments, and improve upon previous theoretical modelling of the latter.

•Jan 1, 2013•0 citations
Recent experiments at the University of Arizona have demonstrated superb control and imaging of flattened superfluids revealing a rich landscape of vortex dynamics. Vortex dipoles have been created and their dynamics observed [Neely et al. Phys. Rev. Lett. 104, 160410 (2010)], and highly charged persistent currents have been formed through a clever combination of stirring and dissipation [T. W. Neely, PhD thesis, (2010)]. Many ultra-cold gas systems, including these, are in a regime that we may characterize as quasi-equilibrium: despite some external forcing, a large fraction of the gas remains in thermal equilibrium. In this thesis we use the stochastic projected Gross-Pitaevskii equation (SPGPE) to make quantitative predictions of the quasi-equilibrium Bose gas. \n\nWe quantitatively compare the SPGPE with experiment by modeling the persistent current formation experiment performed at the University of Arizona [T. W. Neely, PhD thesis, (2010)]. We determine all SPGPE parameters for the toroidal system prior to simulation, enabling quantitative modeling of the experiment with no fitting parameters, giving a true test of the SPGPE theory. We find the SPGPE gives quantitative agreement with experiment, accurately predicting the size of the persistent current as well as the decay time of the vortices. We also observe the crucial role that thermal fluctuations have on enabling this agreement, showing the comprehensive SPGPE treatment is necessary to make quantitatively accurate calculations of quasi-equilibrium systems. This is the first quantitative agreement with experimental observations of vortex dynamics obtained with a theory of dissipation from first principles using no fitting parameters.\n\nWe then systematically study the Kelvin mode excitations on a vortex line in a three dimensional Bose-Einstein condensate using the SPGPE. We give a quantitative measure of the magnitude of vortex bending caused by the activation of Kelvin modes, and find that vortex bending can be suppressed by tightening the confinement along the direction of the vortex line. This leads to a strong suppression of the vortex decay rate as the system enters a regime of two-dimensional vortex dynamics, characterized by a critical oblateness.\n\nIn our final application of the SPGPE we simulate the decay of a vortex dipole. We model a recent experiment of Neely et al. [Neely et al. Phys. Rev. Lett. 104, 160410 (2010)], finding the SPGPE predicts a dipole lifetime consistent with experimental observations. We also show the experiment lies in the two-dimensional regime of vortex dynamics, validating our critical oblateness calculation.
We study the Kelvin mode excitations on a vortex line in a three-dimensional trapped Bose-Einstein condensate at finite temperature. Our stochastic Gross-Pitaevskii simulations show that the activation of these modes can be suppressed by tightening the confinement along the direction of the vortex line, leading to a strong suppression in the vortex decay rate as the system enters a regime of two-dimensional vortex dynamics. As the system approaches the condensation transition temperature, we find that the vortex decay rate is strongly sensitive to dimensionality and temperature, observing a large enhancement for quasi-two-dimensional traps. Three-dimensional simulations of the recent vortex dipole decay experiment of Neely et al. [Phys. Rev. Lett. 104, 160401 (2010)] confirm two-dimensional vortex dynamics and predict a dipole lifetime consistent with experimental observations and suppression of Kelvon-induced vortex decay in highly oblate condensates.
Providing a complete description of dissipative superfluid dynamics is one of the major challenges of many-body quantum field theory. In this thesis we make a fundamental step towards this goal by implementing the stochastic projected Gross-Pitaevskii equation (SPGPE) in complete form for the first time. The SPGPE is a high-temperature theory of Bose-Einstein condensate dynamics, providing a classical-field description of a low-energy subspace in contact with a thermal reservoir. The reservoir interaction terms account for dissipation and noise from thermal interactions, and arise from two distinct processes described as number-damping and energy-damping. This work advances previous applications of the SPGPE theory, which have only included number-damping processes, by implementing the energy-damping processes. We describe the properties of the deterministic and noise terms corresponding to the energy-damping process, and develop a novel algorithm to accurately and efficiently evaluate the energy-damping terms in the SPGPE. We apply the SPGPE to a range of experimentally accessible systems, considering both non-equilibrium and quasi-equilibrium dynamics. We model the experiment of Neely et al. [Phys. Rev. Lett. 111, 235301 (2013)], where stirring of a toroidally trapped Bose-Einstein condensate generates a disordered array of quantum vortices that decay, via thermal dissipation, to form a macroscopic persistent current. We perform numerical simulations of the experiment using the number-damping SPGPE and ab initio determined reservoir parameters. We quantitatively reproduce both the formation time and size of the persistent current, as measured in the experiment. In the first application of the full SPGPE, we consider the non-equilibrium dynamics of a condensate excited into a large-amplitude breathing mode. We find that in such non-equilibrium regimes, the energy-damping dominates over the number-damping process, leading to qualitatively different system dynamics. In particular, energy damping causes the system to rapidly reach thermal equilibrium without greatly depleting the condensate, showing that energy damping provides a highly coherent dissipation mechanism. Finally, we apply the SPGPE to the quasi-equilibrium dynamics of single-vortex decay. Energy-damping processes have previously been neglected for this system. SPGPE simulations show that in fact energy-damping has a dominant effect on the lifetime of a single vortex, with lifetimes less than half those predicted by the number-damping SPGPE. In contrast to the breathing mode decay, we observe little qualitative difference between the energy-damping and number-damping descriptions of vortex decay. Our findings show that while energy-damping processes are important to quantitatively describe quasi-equilibrium dynamics, the system behavior may be described by the number-damping SPGPE with a suitably modified dissipation rate.
Experimental stirring of a toroidally trapped Bose-Einstein condensate at high temperature generates a disordered array of quantum vortices that decays via thermal dissipation to form a macroscopic persistent current [T. W. Neely et al., Phys. Rev. Lett. 111, 235301 (2013)]. We perform three-dimensional numerical simulations of the experimental sequence within the stochastic projected Gross-Pitaevskii equation using ab initio determined reservoir parameters. We find that both damping and noise are essential for describing the dynamics of the high-temperature Bose field. The theory gives a quantitative account of the formation of a persistent current, with no fitted parameters.
The decay of a vortex from a nonrotating high temperature Bose-Einstein condensate is modeled using the stochastic projected Gross-Pitaevskii equation (SPGPE). In order to exploit the tunability of temperature in SPGPE theory while maintaining the total atom number constant, we develop a simple and accurate Hartree-Fock method to estimate the SPGPE parameters for systems close to thermal equilibrium. We then calculate the lifetime of a vortex using three classical field theories that describe vortex decay in different levels of approximation. The SPGPE theory is shown to give the most complete description of the decay process, predicting significantly shorter vortex lifetimes than the alternative theories. Using the SPGPE theory to simulate vortex decay for a trapped gas of $5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ 87Rb^{87}\mathrm{Rb}87Rb atoms, we calculate a vortex lifetime $\mathrm{t\ifmmode \bar{}\else \={}\fi{}}$ that decreases linearly with temperature, falling in the range $20\mathrm{s}>\mathrm{t\ifmmode \bar{}\else \={}\fi{}}>1.5\mathrm{s}$ corresponding to the temperature range $0.78{T}_{c}\ensuremath{\leqslant}T\ensuremath{\leqslant}0.93{T}_{c}$. The vortex lifetimes calculated provide a lower bound for the lifetime of a persistent current with unit winding number in our chosen trap geometry in the limit of vanishing vortex pinning potential.
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)
In this thesis we use the stochastic Gross-Pitaevskii equation (SGPE), a finite temperature model for weakly interacting ultracold Bose gases which fully incorporates density and phase fluctuations, to demonstrate ab initio quantitative agreement with a number of quasi-one-dimensional experiments. To achieve this, we propose and numerically solve a quasi-one-dimensional form of the SGPE, supported by a self-consistent treatment of radially-excited thermal modes. The quasi-one-dimensional stochastic Gross-Pitaevskii equation provides an accurate finite temperature description of the dynamical equilibrium of the lowenergy axial modes of a Bose gas, assumed to be highly populated and thus treated within the ‘classical field’ approximation. This treatment allows to selfconsistently account for transverse, quasi-one-dimensional effects, which makes it a valid model in the regime where the chemical potential, μ, is approximately equal to a few times the transverse excitation energy, ~ω⊥. In the regime where the thermal energy, kBT , is also comparable to or larger than ~ω⊥, the transverse excited states play an increasingly important role, and are treated here as onedimensional independent Bose gases at static equilibrium. Firstly, we demonstrate that this is an excellentmodel for ab initio investigation of equilibrium properties, such as density profiles and density fluctuations. This is shown by accurately reproducing the in situ density profiles recently obtained in the experiments of Trebbia et al. [Phys. Rev. Lett. 97, 250403 (2006)] and van Amerongen et al. [Phys. Rev. Lett. 100, 090402 (2008)], and the density fluctuation data reported by Armijo et al. [Phys. Rev. Lett. 105, 230402 (2010)]. Moreover, we perform an ab initio analysis of the temperature dependence of the phase coherence of finite temperature, quasi-one-dimensional Bose gases measured in the experiments of Richard et al. [Phys. Rev. Lett. 91, 010405 (2003)] and Hugbart et al. [Eur. Phys. J. D 35, 155 (2005)]. We find very good agreement across the entire observed temperature range in both experiments, and improve upon previous theoretical modelling of the latter.