Ashton S Bradley

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(Received 00 Month 200x; In final form 00 Month 200x) We review phase space techniques based on the Wigner representation that provide an approximate description of dilute ultra-cold Bose gases. In this approach the quantum field evolution can be represented using equations of motion of a similar form to the Gross-Pitaevskii equation but with stochastic(More)
1 Phase transitions are ubiquitous in nature, and can be arranged into universality classes such that systems having unrelated microscopic physics show identical scaling behaviour near the critical point. One prominent universal element of many continuous phase transitions is the spontaneous formation of topological defects during a quench through the(More)
We develop a stochastic Gross-Pitaveskii theory suitable for the study of Bose-Einstein condensation in a rotating dilute Bose gas. The theory is used to model the dynamical and equilibrium properties of a rapidly rotating Bose gas quenched through the critical point for condensation, as in the experiment of Haljan et al. In contrast to stirring a(More)
We examine the tripartite entanglement properties of an optical system using interlinked ␹ ͑2͒ interactions, recently studied experimentally in terms of its phase-matching properties by Bondani et al. ͓Opt. Express 14, 21, 9838 ͑2006͔͒. We show that the system produces output modes at three distinct frequencies which are genuinely tripartite entangled, and(More)
We study conditions under which vortices in a highly oblate harmonically trapped Bose-Einstein condensate (BEC) can be stabilized due to pinning by a blue-detuned Gaussian laser beam, with particular emphasis on the potentially destabilizing effects of laser beam positioning within the BEC. Our approach involves theoretical and numerical exploration of(More)
We present Ehrenfest relations for the high temperature stochastic Gross– Pitaevskii equation description of a trapped Bose gas, including the effect of growth noise and the energy cutoff. A condition for neglecting the cutoff terms in the Ehrenfest relations is found which is more stringent than the usual validity condition of the truncated Wigner or(More)
We investigate the quantum properties of the well-known process of sum frequency generation, showing that it is potentially a very useful source of nonclassical states of the electromagnetic field, some of which are not possible with the more common techniques. We show that it can produce quadrature squeezed light, bright bichromatic entangled states, and(More)
The process of cascaded down-conversion and sum-frequency generation inside an optical cavity has been predicted to be a potential source of three-mode continuous-variable entanglement. When the cavity is pumped by two fields, the threshold properties have been analyzed, showing that these are more complicated than in well-known processes such as optical(More)
Fluids subjected to suitable forcing will exhibit turbulence, with characteristics strongly affected by the fluid's physical properties and dimensionality. In this work, we explore two-dimensional (2D) quantum turbulence in an oblate Bose-Einstein condensate confined to an annular trapping potential. Experimentally, we find conditions for which small-scale(More)
We present a quantum-mechanical treatment of the mechanical stirring of Bose-Einstein condensates using classical field techniques. In our approach the condensate and excited modes are described using a Hamiltonian classical field method in which the atom number and ͑rotating frame͒ energy are strictly conserved. We simulate a T = 0 quasi-two-dimensional(More)