2018
- Quantum Turbulence in a Planar Bose–Einstein Condensate,
S. P. Johnstone, PhD Thesis.
, 2018.
[DOI] [Bibtex] [Abstract]
Lars Onsager noted that turbulent fluids constrained to flow in two dimensions tend to develop large-scale features. Quantum fluids, such as atomic Bose–Einstein condensates, also feature turbulent flows, however their vortices behave as discrete point-like particles. This thesis presents the results of experiments on the distribution of quantised vortices in highly oblate, uniform Bose-Einstein condensates. Initially randomly distributed vortices were observed to rearrange themselves to become more ordered, resembling Onsager’s description of large-scale flow features. These results add to our current understanding of the physical processes involved in turbulent flows of superfluids.
@phdthesis{johnstone_quantum_2018, title = {Quantum Turbulence in a Planar {Bose}–{Einstein} Condensate}, url = {https://figshare.com/articles/Quantum_Turbulence_in_a_Planar_Bose_Einstein_Condensate/7471580}, abstract = {Lars Onsager noted that turbulent fluids constrained to flow in two dimensions tend to develop large-scale features. Quantum fluids, such as atomic Bose–Einstein condensates, also feature turbulent flows, however their vortices behave as discrete point-like particles. This thesis presents the results of experiments on the distribution of quantised vortices in highly oblate, uniform Bose-Einstein condensates. Initially randomly distributed vortices were observed to rearrange themselves to become more ordered, resembling Onsager’s description of large-scale flow features. These results add to our current understanding of the physical processes involved in turbulent flows of superfluids.}, urldate = {2018-12-17TZ}, author = {Johnstone, Shaun Phillip}, month = dec, year = {2018}, doi = {10.26180/5c171b9ecdb9c}, keywords = {Bose-Einstein condensate, Quantum turbulence, vortices} }
- State-dependent forces in cold quantum gases,
C. J. Billington, PhD Thesis.
[DOI] [Bibtex] [Abstract]
This thesis develops a new way of modelling atoms that behave quantum mechanically on the inside, but classically on the outside. Doing so makes modelling the salient physics tractable. Prior to this technique, treating the outside of an atom classically failed to reproduce a bedrock experiment of quantum mechanics—the Stern–Gerlach experiment. I also report on the conception and flourishing of a control and analysis software suite for experiments in quantum science. This open-source project empowers experimenters to compose human-readable narratives upon their apparatus and has been adopted by a dozen groups worldwide.
@phdthesis{billington_state-dependent_2018, title = {State-dependent forces in cold quantum gases}, url = {https://figshare.com/articles/State-dependent_forces_in_cold_quantum_gases/7264406}, abstract = {This thesis develops a new way of modelling atoms that behave quantum mechanically on the inside, but classically on the outside. Doing so makes modelling the salient physics tractable. Prior to this technique, treating the outside of an atom classically failed to reproduce a bedrock experiment of quantum mechanics—the Stern–Gerlach experiment. I also report on the conception and flourishing of a control and analysis software suite for experiments in quantum science. This open-source project empowers experimenters to compose human-readable narratives upon their apparatus and has been adopted by a dozen groups worldwide.}, urldate = {2018-12-13TZ}, school = {Monash University}, author = {Billington, Christopher James}, month = oct, year = {2018}, doi = {10.26180/5bd68acaf0696}, keywords = {Bose-Einstein condensation, cold atoms, laser cooling, semiclassical models} }
- Equations of state from individual one-dimensional Bose gases,
F. Salces-Carcoba, C. J. Billington, A. Putra, Y. Yue, S. Sugawa, and I. B. Spielman.
[arXiv] [Bibtex] [Abstract]
We trap individual 1D Bose gases and obtain the associated equation of state by combining calibrated confining potentials with in-situ density profiles. Our observations agree well with the exact Yang-Yang 1D thermodynamic solutions under the local density approximation. We find that our final 1D system undergoes inefficient evaporative cooling that decreases the absolute temperature, but monotonically reduces a degeneracy parameter.
@article{salces-carcoba_equations_2018, title = {Equations of state from individual one-dimensional {Bose} gases}, url = {http://arxiv.org/abs/1808.06933}, abstract = {We trap individual 1D Bose gases and obtain the associated equation of state by combining calibrated confining potentials with in-situ density profiles. Our observations agree well with the exact Yang-Yang 1D thermodynamic solutions under the local density approximation. We find that our final 1D system undergoes inefficient evaporative cooling that decreases the absolute temperature, but monotonically reduces a degeneracy parameter.}, urldate = {2018-08-22TZ}, journal = {arXiv:1808.06933 [cond-mat, physics:physics]}, author = {Salces-Carcoba, F. and Billington, C. J. and Putra, A. and Yue, Y. and Sugawa, S. and Spielman, I. B.}, month = aug, year = {2018}, eprint = {1808.06933}, keywords = {Condensed Matter - Quantum Gases, Physics - Atomic Physics} }
- Motion of vortices in inhomogeneous Bose–Einstein condensates,
A. J. Groszek, D. M. Paganin, K. Helmerson, and T. P. Simula.
Physical Review A 97, 23617 (2018).
[arXiv] [DOI] [Bibtex] [Abstract]
We derive a general and exact equation of motion for a quantized 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.
@article{groszek_motion_2018, title = {Motion of vortices in inhomogeneous {Bose--Einstein} condensates}, volume = {97}, url = {https://link.aps.org/doi/10.1103/PhysRevA.97.023617}, doi = {10.1103/PhysRevA.97.023617}, abstract = {We derive a general and exact equation of motion for a quantized 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.}, number = {2}, urldate = {2018-03-14TZ}, journal = {Physical Review A}, author = {Groszek, Andrew J. and Paganin, David M. and Helmerson, Kristian and Simula, Tapio P.}, month = feb, year = {2018}, eprint = {1708.09202}, pages = {023617} }
- Order from chaos: Observation of large-scale flow from turbulence in a two-dimensional superfluid,
S. P. Johnstone, A. J. Groszek, P. T. Starkey, C. J. Billington, T. P. Simula, and K. Helmerson.
[arXiv] [Bibtex] [Abstract]
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.
@article{johnstone_order_2018, title = {Order from chaos: Observation of large-scale flow from turbulence in a two-dimensional superfluid}, url = {http://arxiv.org/abs/1801.06952}, abstract = {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.}, urldate = {2018-01-23TZ}, journal = {arXiv:1801.06952 [cond-mat, physics:physics]}, author = {Johnstone, Shaun P. and Groszek, Andrew J. and Starkey, Philip T. and Billington, Christopher J. and Simula, Tapio P. and Helmerson, Kristian}, month = jan, year = {2018}, eprint = {1801.06952}, keywords = {Condensed Matter - Quantum Gases, Physics - Fluid Dynamics} }
- Vortex Thermometry for Turbulent Two-Dimensional Fluids,
A. J. Groszek, M. J. Davis, D. M. Paganin, K. Helmerson, and T. P. Simula.
Physical Review Letters 120, 34504 (2018).
[arXiv] [DOI] [Bibtex] [Abstract]
We introduce a new method of statistical analysis to characterize 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 we apply this vortex thermometry to characterize 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 we find previously unidentified vortex power-law distributions that emerge from the dynamics.
@article{groszek_vortex_2018, title = {Vortex Thermometry for Turbulent Two-Dimensional Fluids}, volume = {120}, url = {https://link.aps.org/doi/10.1103/PhysRevLett.120.034504}, doi = {10.1103/PhysRevLett.120.034504}, abstract = {We introduce a new method of statistical analysis to characterize 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 we apply this vortex thermometry to characterize 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 we find previously unidentified vortex power-law distributions that emerge from the dynamics.}, number = {3}, urldate = {2018-01-21TZ}, journal = {Physical Review Letters}, author = {Groszek, Andrew J. and Davis, Matthew J. and Paganin, David M. and Helmerson, Kristian and Simula, Tapio P.}, month = jan, year = {2018}, eprint = {1702.05229}, pages = {034504} }
2017
- Precise wave-function engineering with magnetic resonance,
P. B. Wigley, L. M. Starkey, S. S. Szigeti, M. Jasperse, J. J. Hope, L. D. Turner, and R. P. Anderson.
Physical Review A 96, 13612 (2017).
[arXiv] [DOI] [Bibtex] [Abstract]
Controlling quantum fluids at their fundamental length scale will yield superlative quantum simulators, precision sensors, and spintronic devices. This scale is typically below the optical diffraction limit, precluding precise wave-function engineering using optical potentials alone. We present a protocol to rapidly control the phase and density of a quantum fluid down to the healing length scale using strong time-dependent coupling between internal states of the fluid in a magnetic field gradient. We demonstrate this protocol by simulating the creation of a single stationary soliton and double soliton states in a Bose-Einstein condensate with control over the individual soliton positions and trajectories, using experimentally feasible parameters. Such states are yet to be realized experimentally, and are a path towards engineering soliton gases and exotic topological excitations.
@article{wigley_precise_2017, title = {Precise wave-function engineering with magnetic resonance}, volume = {96}, url = {https://link.aps.org/doi/10.1103/PhysRevA.96.013612}, doi = {10.1103/PhysRevA.96.013612}, abstract = {Controlling quantum fluids at their fundamental length scale will yield superlative quantum simulators, precision sensors, and spintronic devices. This scale is typically below the optical diffraction limit, precluding precise wave-function engineering using optical potentials alone. We present a protocol to rapidly control the phase and density of a quantum fluid down to the healing length scale using strong time-dependent coupling between internal states of the fluid in a magnetic field gradient. We demonstrate this protocol by simulating the creation of a single stationary soliton and double soliton states in a Bose-Einstein condensate with control over the individual soliton positions and trajectories, using experimentally feasible parameters. Such states are yet to be realized experimentally, and are a path towards engineering soliton gases and exotic topological excitations.}, number = {1}, journal = {Physical Review A}, author = {Wigley, P. B. and Starkey, L. M. and Szigeti, S. S. and Jasperse, M. and Hope, J. J. and Turner, L. D. and Anderson, R. P.}, month = jul, year = {2017}, eprint = {1412.6854}, pages = {013612} }
- High efficiency, low cost holographic optical elements for ultracold atom trapping,
S. Tempone-Wiltshire, S. Johnstone, and K. Helmerson.
Optics Express 25, 296–304 (2017).
[DOI] [Bibtex] [Abstract]
We demonstrate a method of creating high efficiency, high fidelity, holographic optical elements for the generation of complex optical fields, in a low cost photopolymer, Bayfol HX. The desired optical field profile is generated by a spatial light modulator and written into an optically addressable photopolymer as a volume hologram. We demonstrate the utility of this approach by trapping a Bose-Einstein condensate of rubidium-87 atoms in the nodal plane of an HG0,1 mode generated by one of these holographic optical elements. We also extend this method to the generation holograms with twice the angular momentum per photon than can be generated with a given spatial light modulator.
@article{tempone-wiltshire_high_2017, title = {High efficiency, low cost holographic optical elements for ultracold atom trapping}, volume = {25}, copyright = {© 2017 Optical Society of America}, issn = {1094-4087}, url = {http://www.osapublishing.org/abstract.cfm?uri=oe-25-1-296}, doi = {10.1364/OE.25.000296}, abstract = {We demonstrate a method of creating high efficiency, high fidelity, holographic optical elements for the generation of complex optical fields, in a low cost photopolymer, Bayfol HX. The desired optical field profile is generated by a spatial light modulator and written into an optically addressable photopolymer as a volume hologram. We demonstrate the utility of this approach by trapping a Bose-Einstein condensate of rubidium-87 atoms in the nodal plane of an HG0,1 mode generated by one of these holographic optical elements. We also extend this method to the generation holograms with twice the angular momentum per photon than can be generated with a given spatial light modulator.}, language = {EN}, number = {1}, urldate = {2017-01-04TZ}, journal = {Optics Express}, author = {Tempone-Wiltshire, Sebastien and Johnstone, Shaun and Helmerson, Kristian}, month = jan, year = {2017}, pages = {296--304} }
2016
- Precise engineering of the Bose–Einstein condensate wavefunction using magnetic resonance control,
L. M. Starkey, PhD Thesis.
[DOI] [Bibtex] [Abstract]
This thesis develops a new way to sculpt the coldest matter in the universe, a Bose-Einstein condensate, using methods inspired by the medical diagnostic technique of magnetic resonance imaging. This superfluid matter, first predicted by Bose and Einstein in 1925, manifests quantum behaviour at the macroscopic scale. We demonstrate how to shape the finest structures into this matter with unprecedented control, with the future goal of observing structures which have never been created before in quantum fluids, and causing this matter to mimic other physical phenomena.
@phdthesis{starkey_precise_2016, type = {{PhD} thesis}, title = {Precise engineering of the {Bose--Einstein} condensate wavefunction using magnetic resonance control}, url = {http://dx.doi.org/1959.1/1278937}, abstract = {This thesis develops a new way to sculpt the coldest matter in the universe, a Bose-Einstein condensate, using methods inspired by the medical diagnostic technique of magnetic resonance imaging. This superfluid matter, first predicted by Bose and Einstein in 1925, manifests quantum behaviour at the macroscopic scale. We demonstrate how to shape the finest structures into this matter with unprecedented control, with the future goal of observing structures which have never been created before in quantum fluids, and causing this matter to mimic other physical phenomena.}, school = {Monash University}, author = {Starkey, L. M.}, month = jul, year = {2016}, doi = {1959.1/1278937} }
- Optical vortex knots – one photon at a time,
S. J. Tempone-Wiltshire, S. P. Johnstone, and K. Helmerson.
Scientific Reports 6, 24463 (2016).
[DOI] [Bibtex] [Abstract]
Feynman described the double slit experiment as “a phenomenon which is impossible, absolutely impossible, to explain in any classical way and which has in it the heart of quantum mechanics”. The double-slit experiment, performed one photon at a time, dramatically demonstrates the particle-wave duality of quantum objects by generating a fringe pattern corresponding to the interference of light (a wave phenomenon) from two slits, even when there is only one photon (a particle) at a time passing through the apparatus. The particle-wave duality of light should also apply to complex three dimensional optical fields formed by multi-path interference, however, this has not been demonstrated. Here we observe particle-wave duality of a three dimensional field by generating a trefoil optical vortex knot – one photon at a time. This result demonstrates a fundamental physical principle, that particle-wave duality implies interference in both space (between spatially distinct modes) and time (through the complex evolution of the superposition of modes), and has implications for topologically entangled single photon states, orbital angular momentum multiplexing and topological quantum computing.
@article{tempone-wiltshire_optical_2016, title = {Optical vortex knots – one photon at a time}, volume = {6}, issn = {2045-2322}, url = {http://www.nature.com/articles/srep24463}, doi = {10.1038/srep24463}, abstract = {Feynman described the double slit experiment as “a phenomenon which is impossible, absolutely impossible, to explain in any classical way and which has in it the heart of quantum mechanics”. The double-slit experiment, performed one photon at a time, dramatically demonstrates the particle-wave duality of quantum objects by generating a fringe pattern corresponding to the interference of light (a wave phenomenon) from two slits, even when there is only one photon (a particle) at a time passing through the apparatus. The particle-wave duality of light should also apply to complex three dimensional optical fields formed by multi-path interference, however, this has not been demonstrated. Here we observe particle-wave duality of a three dimensional field by generating a trefoil optical vortex knot – one photon at a time. This result demonstrates a fundamental physical principle, that particle-wave duality implies interference in both space (between spatially distinct modes) and time (through the complex evolution of the superposition of modes), and has implications for topologically entangled single photon states, orbital angular momentum multiplexing and topological quantum computing.}, urldate = {2016-04-18TZ}, journal = {Scientific Reports}, author = {Tempone-Wiltshire, Sebastien J. and Johnstone, Shaun P. and Helmerson, Kristian}, month = apr, year = {2016}, pages = {24463} }
- Onsager vortex formation in Bose–Einstein condensates in two-dimensional power-law traps,
A. J. Groszek, T. P. Simula, D. M. Paganin, and K. Helmerson.
Physical Review A 93, 43614 (2016).
[arXiv] [DOI] [Bibtex] [Abstract]
We study computationally dynamics of quantized 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.
@article{groszek_onsager_2016, title = {Onsager vortex formation in {Bose--Einstein} condensates in two-dimensional power-law traps}, volume = {93}, url = {http://link.aps.org/doi/10.1103/PhysRevA.93.043614}, doi = {10.1103/PhysRevA.93.043614}, abstract = {We study computationally dynamics of quantized 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.}, number = {4}, urldate = {2016-04-18TZ}, journal = {Physical Review A}, author = {Groszek, Andrew J. and Simula, Tapio P. and Paganin, David M. and Helmerson, Kristian}, month = apr, year = {2016}, eprint = {1511.06552}, pages = {043614} }
2015
- A Monte Carlo wavefunction method for semiclassical simulations of spin-position entanglement,
C. J. Billington, C. J. Watkins, R. P. Anderson, and L. D. Turner.
[arXiv] [Bibtex] [Abstract]
We present a Monte Carlo wavefunction method for semiclassically modeling spin-\${\textbackslash}frac12\$ systems in a magnetic field gradient in one dimension. Our model resolves the conflict of determining what classical force an atom should be subjected to when it is in an arbitrary superposition of internal states. Spatial degrees of freedom are considered to be an environment, entanglement with which decoheres the internal states. Atoms follow classical trajectories through space, punctuated by probabilistic jumps between spin states. We modify the conventional Monte Carlo wavefunction method to jump between states when population transfer occurs, rather than when population is later discarded via exponential decay. This results in a spinor wavefunction that is continuous in time, and allows us to model the classical particle trajectories (evolution of the environment variables) more accurately. The model is not computationally demanding and it agrees well with simulations of the full spatial wavefunction of an atom.
@article{billington_monte_2015, title = {{A} Monte Carlo wavefunction method for semiclassical simulations of spin-position entanglement}, url = {http://arxiv.org/abs/1502.06674}, abstract = {We present a Monte Carlo wavefunction method for semiclassically modeling spin-\${\textbackslash}frac12\$ systems in a magnetic field gradient in one dimension. Our model resolves the conflict of determining what classical force an atom should be subjected to when it is in an arbitrary superposition of internal states. Spatial degrees of freedom are considered to be an environment, entanglement with which decoheres the internal states. Atoms follow classical trajectories through space, punctuated by probabilistic jumps between spin states. We modify the conventional Monte Carlo wavefunction method to jump between states when population transfer occurs, rather than when population is later discarded via exponential decay. This results in a spinor wavefunction that is continuous in time, and allows us to model the classical particle trajectories (evolution of the environment variables) more accurately. The model is not computationally demanding and it agrees well with simulations of the full spatial wavefunction of an atom.}, urldate = {2016-01-04TZ}, journal = {arXiv:1502.06674}, author = {Billington, C. J. and Watkins, C. J. and Anderson, R. P. and Turner, L. D.}, month = feb, year = {2015}, eprint = {1502.06674}, keywords = {Physics - Atomic Physics, Quantum Physics} }
2014
- Emergence of Order from Turbulence in an Isolated Planar Superfluid,
T. Simula, M. J. Davis, and K. Helmerson.
Physical Review Letters 113, 165302 (2014).
[arXiv] [DOI] [Bibtex] [Abstract]
We study the relaxation dynamics of an isolated zero temperature quasi-two-dimensional superfluid Bose-Einstein condensate that is imprinted with a spatially random distribution of quantum vortices. Following a period of vortex annihilation the remaining vortices self-organize into two macroscopic coherent “Onsager vortex” clusters that are stable indefinitely—despite the absence of driving or external dissipation in the dynamics. We demonstrate that this occurs due to a novel physical mechanism—the evaporative heating of the vortices—that results in a negative-temperature phase transition in the vortex degrees of freedom. At the end of our simulations the system is trapped in a nonthermal state. Our computational results provide a pathway to observing Onsager vortex states in a superfluid Bose gas.
@article{simula_emergence_2014, title = {Emergence of Order from Turbulence in an Isolated Planar Superfluid}, volume = {113}, url = {http://link.aps.org/doi/10.1103/PhysRevLett.113.165302}, doi = {10.1103/PhysRevLett.113.165302}, abstract = {We study the relaxation dynamics of an isolated zero temperature quasi-two-dimensional superfluid Bose-Einstein condensate that is imprinted with a spatially random distribution of quantum vortices. Following a period of vortex annihilation the remaining vortices self-organize into two macroscopic coherent “Onsager vortex” clusters that are stable indefinitely—despite the absence of driving or external dissipation in the dynamics. We demonstrate that this occurs due to a novel physical mechanism—the evaporative heating of the vortices—that results in a negative-temperature phase transition in the vortex degrees of freedom. At the end of our simulations the system is trapped in a nonthermal state. Our computational results provide a pathway to observing Onsager vortex states in a superfluid Bose gas.}, number = {16}, urldate = {2016-01-04TZ}, journal = {Physical Review Letters}, author = {Simula, Tapio and Davis, Matthew J. and Helmerson, Kristian}, month = oct, year = {2014}, eprint = {1405.3399}, pages = {165302} }
- Condensed-matter physics: History matters for a stirred superfluid,
M. J. Davis and K. Helmerson.
Nature 506, 166–167 (2014).
[DOI] [Bibtex] [Abstract]
The observation of path dependence in the response of a superfluid to stirring promises potential applications in precision rotation sensing, and provides a test bed for microscopic theories of ultracold atomic gases. See Letter p.200
@article{davis_condensed-matter_2014, title = {Condensed-matter physics: History matters for a stirred superfluid}, volume = {506}, copyright = {© 2014 Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.}, issn = {0028-0836}, shorttitle = {Condensed-matter physics}, url = {http://www.nature.com/nature/journal/v506/n7487/full/506166a.html}, doi = {10.1038/506166a}, abstract = {The observation of path dependence in the response of a superfluid to stirring promises potential applications in precision rotation sensing, and provides a test bed for microscopic theories of ultracold atomic gases. See Letter p.200}, number = {7487}, urldate = {2016-01-04TZ}, journal = {Nature}, author = {Davis, Matthew J. and Helmerson, Kristian}, month = feb, year = {2014}, pages = {166--167} }
2013
- A scripted control system for autonomous hardware-timed experiments,
P. T. Starkey, C. J. Billington, S. P. Johnstone, M. Jasperse, K. Helmerson, L. D. Turner, and R. P. Anderson.
Review of Scientific Instruments 84, 85111 (2013).
[arXiv] [DOI] [Bibtex] [Abstract]
We present the labscript suite, an open-source experiment control system for automating shot-based experiments and their analysis. Experiments are composed as Python code, which is used to produce low-level hardware instructions. They are queued up and executed on the hardware in real time, synchronized by a pseudoclock. Experiment parameters are manipulated graphically, and analysis routines are run as new data are acquired. With this system, we can easily automate exploration of parameter spaces, including closed-loop optimization.
@article{starkey_scripted_2013, title = {{A} scripted control system for autonomous hardware-timed experiments}, volume = {84}, issn = {0034-6748, 1089-7623}, url = {http://scitation.aip.org/content/aip/journal/rsi/84/8/10.1063/1.4817213}, doi = {10.1063/1.4817213}, abstract = {We present the labscript suite, an open-source experiment control system for automating shot-based experiments and their analysis. Experiments are composed as Python code, which is used to produce low-level hardware instructions. They are queued up and executed on the hardware in real time, synchronized by a pseudoclock. Experiment parameters are manipulated graphically, and analysis routines are run as new data are acquired. With this system, we can easily automate exploration of parameter spaces, including closed-loop optimization.}, number = {8}, urldate = {2014-04-25TZ}, journal = {Review of Scientific Instruments}, author = {Starkey, P. T. and Billington, C. J. and Johnstone, S. P. and Jasperse, M. and Helmerson, K. and Turner, L. D. and Anderson, R. P.}, month = aug, year = {2013}, eprint = {1303.0080}, pages = {085111} }
- A versatile high resolution objective for imaging quantum gases,
L. M. Bennie, P. T. Starkey, M. Jasperse, C. J. Billington, R. P. Anderson, and L. D. Turner.
Optics Express 21, 9011–9016 (2013).
[arXiv] [DOI] [Bibtex] [Abstract]
We present a high resolution objective lens made entirely from catalog singlets that has a numerical aperture of 0.36. It corrects for aberrations introduced by a glass window and has a long working distance of 35 mm, making it suitable for imaging objects within a vacuum system. This offers simple high resolution imaging for many in the quantum gas community. The objective achieves a resolution of 1.3 μm at the design wavelength of 780 nm, and a diffraction-limited field of view of 360 μm when imaging through a 5 mm thick window. Images of a resolution target and a pinhole show quantitative agreement with the simulated lens performance. The objective is suitable for diffraction-limited monochromatic imaging on the D2 line of all the alkalis by changing only the aperture diameter, retaining numerical apertures above 0.32. The design corrects for window thicknesses of up to 15 mm if the singlet spacings are modified.
@article{bennie_versatile_2013, title = {{A} versatile high resolution objective for imaging quantum gases}, volume = {21}, url = {http://www.opticsexpress.org/abstract.cfm?URI=oe-21-7-9011}, doi = {10.1364/OE.21.009011}, abstract = {We present a high resolution objective lens made entirely from catalog singlets that has a numerical aperture of 0.36. It corrects for aberrations introduced by a glass window and has a long working distance of 35 mm, making it suitable for imaging objects within a vacuum system. This offers simple high resolution imaging for many in the quantum gas community. The objective achieves a resolution of 1.3 μm at the design wavelength of 780 nm, and a diffraction-limited field of view of 360 μm when imaging through a 5 mm thick window. Images of a resolution target and a pinhole show quantitative agreement with the simulated lens performance. The objective is suitable for diffraction-limited monochromatic imaging on the D2 line of all the alkalis by changing only the aperture diameter, retaining numerical apertures above 0.32. The design corrects for window thicknesses of up to 15 mm if the singlet spacings are modified.}, number = {7}, urldate = {2014-04-25TZ}, journal = {Optics Express}, author = {Bennie, L. M. and Starkey, P. T. and Jasperse, M. and Billington, C. J. and Anderson, R. P. and Turner, L. D.}, month = apr, year = {2013}, eprint = {1302.4166}, pages = {9011--9016} }
2012
- Partial-transfer absorption imaging: A versatile technique for optimal imaging of ultracold gases,
A. Ramanathan, S. R. Muniz, K. C. Wright, R. P. Anderson, W. D. Phillips, K. Helmerson, and G. K. Campbell.
Review of Scientific Instruments 83, 83119 (2012).
[arXiv] [DOI] [Bibtex] [Abstract]
Partial-transfer absorption imaging is a tool that enables optimal imaging of atomic clouds for a wide range of optical depths. In contrast to standard absorption imaging, the technique can be minimally destructive and can be used to obtain multiple successive images of the same sample. The technique involves transferring a small fraction of the sample from an initial internal atomic state to an auxiliary state and subsequently imaging that fraction absorptively on a cycling transition. The atoms remaining in the initial state are essentially unaffected. We demonstrate the technique, discuss its applicability, and compare its performance as a minimally destructive technique to that of phase-contrast imaging.
@article{ramanathan_partial-transfer_2012, title = {Partial-transfer absorption imaging: {A} versatile technique for optimal imaging of ultracold gases}, volume = {83}, issn = {0034-6748, 1089-7623}, shorttitle = {Partial-transfer absorption imaging}, url = {http://scitation.aip.org/content/aip/journal/rsi/83/8/10.1063/1.4747163}, doi = {10.1063/1.4747163}, abstract = {Partial-transfer absorption imaging is a tool that enables optimal imaging of atomic clouds for a wide range of optical depths. In contrast to standard absorption imaging, the technique can be minimally destructive and can be used to obtain multiple successive images of the same sample. The technique involves transferring a small fraction of the sample from an initial internal atomic state to an auxiliary state and subsequently imaging that fraction absorptively on a cycling transition. The atoms remaining in the initial state are essentially unaffected. We demonstrate the technique, discuss its applicability, and compare its performance as a minimally destructive technique to that of phase-contrast imaging.}, number = {8}, urldate = {2014-04-25TZ}, journal = {Review of Scientific Instruments}, author = {Ramanathan, Anand and Muniz, Sérgio R. and Wright, Kevin C. and Anderson, Russell P. and Phillips, William D. and Helmerson, Kristian and Campbell, Gretchen K.}, month = aug, year = {2012}, eprint = {1206.7048}, pages = {083119} }
2011
- Rotating Atoms with Light
K. Helmerson and W. D. Phillips.
In Twisted Photons, J. P. Torres and L. Torner, editors. Wiley-VCH Verlag GmbH & Co. KGaA, 2011, p. 213–235.
[DOI] [Bibtex] [Abstract]
This chapter explains the techniques developed for manipulating and observing the rotational states of atoms using lasers beams that carry orbital angular momentum (OAM). It describes applications of these techniques for generating and studying persistent currents in a superfluid atomic gas confined in a ring-shaped container. In the case of linear momentum, the mechanical effects of light range from comet tails to laser cooling of atoms. The creation of Bose-Einstein condensates (BECs) in dilute atomic vapors is one of the major triumphs of the quest to control atoms. The chapter describes experiments generating vortex states of higher angular momentum and vortex states in spinor BECs. It also describes a matter wave amplification experiment on a vortex state. Although vortices have been generated and observed in atomic quantum degenerate gases, the related phenomena of persistent or supercurrents have not been clearly observed in atomic BECs.
@incollection{helmerson_rotating_2011, title = {Rotating Atoms with Light}, copyright = {Copyright © 2011 Wiley-VCH Verlag GmbH \& Co. KGaA}, isbn = {978-3-527-63536-8}, url = {http://onlinelibrary.wiley.com/doi/10.1002/9783527635368.ch12/summary}, abstract = {This chapter explains the techniques developed for manipulating and observing the rotational states of atoms using lasers beams that carry orbital angular momentum (OAM). It describes applications of these techniques for generating and studying persistent currents in a superfluid atomic gas confined in a ring-shaped container. In the case of linear momentum, the mechanical effects of light range from comet tails to laser cooling of atoms. The creation of Bose-Einstein condensates (BECs) in dilute atomic vapors is one of the major triumphs of the quest to control atoms. The chapter describes experiments generating vortex states of higher angular momentum and vortex states in spinor BECs. It also describes a matter wave amplification experiment on a vortex state. Although vortices have been generated and observed in atomic quantum degenerate gases, the related phenomena of persistent or supercurrents have not been clearly observed in atomic BECs.}, urldate = {2016-01-04TZ}, booktitle = {Twisted Photons}, publisher = {Wiley-VCH Verlag GmbH \& Co. KGaA}, author = {Helmerson, Kristian and Phillips, William D.}, editor = {Torres, Juan P. and Torner, Lluis}, year = {2011}, doi = {10.1002/9783527635368.ch12}, pages = {213--235} }
Honours Theses
- Sebastien Tempone-Wiltshire, Towards the generation of knotted vortices in a Bose-Einstein condensate, 2014.
- Patrick Vann, Pyramidal magneto-optical traps, 2013.
- Shaun Johnstone, Design of an optical system for the fluorescence imaging of tracer particles in a Bose-Einstein condensate, 2010.
- Chris Billington, Particle velocimetry of vortices in Bose-Einstein condensates, 2010.