Showing papers by "K. Burnett published in 1999"
TL;DR: In this paper, a simple quantitative model of vortex dynamics is presented, which accurately describes the full vortex dynamics, including a critical angular speed of stirring for vortex formation, and a method for experimentally preparing a condensate in a central vortex state is suggested.
Abstract: Simulations of a rotationally stirred condensate show that a regime of simple behaviour occurs in which a single vortex cycles in and out of the condensate. We present a simple quantitative model of this behaviour, which accurately describes the full vortex dynamics, including a critical angular speed of stirring for vortex formation. A method for experimentally preparing a condensate in a central vortex state is suggested.
90 citations
TL;DR: In this article, an extension of the well-known BCS-theory to systems with trapped fermionic atoms is presented. But the theory does not consider the quantized energy levels in the trap.
Abstract: We develop an extension of the well-known BCS-theory to systems with trapped fermionic atoms. The theory fully includes the quantized energy levels in the trap. The key ingredient is to model the attractive interaction between two atoms by a pseudo-potential which leads to a well defined scattering problem and consequently to a BCS-theory free of divergences. We present numerical results for the BCS critical temperature and the temperature dependence of the gap. They are used as a test of existing semi-classical approximations.
86 citations
TL;DR: In this article, the authors realized a quantum accelerator mode using a system consisting of ultracold cesium atoms falling through a pulsed standing wave of off resonant light.
Abstract: We have realized a quantum accelerator mode using a system consisting of ultracold cesium atoms falling through a pulsed standing wave of off resonant light. We present a picture of this system based on diffraction and show that the effect arises from the application of blazed matter wave diffraction gratings. The implications of our results for quantum chaos and the prospect of constructing a large angular separation matter wave beam splitter are discussed.
85 citations
TL;DR: In this paper, the authors demonstrate Berry's phase in an atomic state interacting with a laser field and draw an analogy between this system and that of a spin interaction with a directionally varying magnetic field.
Abstract: We report on the demonstration of Berry's phase in an atomic state interacting with a laser field. We draw an analogy between this system and that of a spin interacting with a directionally varying magnetic field. This allows us to identify an effective magnetic quantum number for the atom-light system that governs the maximum Berry phase the atomic state can acquire. We realize two systems that have different effective magnetic quantum numbers, and use a recently developed atom interferometer to make measurements of Berry's phase.
48 citations
TL;DR: In this article, a straight forward numerical technique, based on the Gross-Pitaevskii equation, is used to generate a self-consistent description of thermally-excited states of a dilute boson gas.
Abstract: A straight forward numerical technique, based on the Gross-Pitaevskii equation, is used to generate a self-consistent description of thermally-excited states of a dilute boson gas. The process of evaporative cooling is then modelled by following the time evolution of the system using the same equation. It is shown that the subsequent rethermalisation of the thermally-excited state produces a cooler coherent condensate. Other results presented show that trapping vortex states with the ground state may be possible in a two-dimensional experimental environment.
38 citations
TL;DR: In this paper, a consistent phase standard for Bose-Einstein condensates is defined and the existence of such a phase standard gives a precise definition to the phase of a condensate.
Abstract: We discuss how a consistent phase standard for Bose-Einstein condensates may be defined show that it has the properties we would wish for in a phase standard: it is not corrupted by subse comparisons. A quantum jump technique is employed to study the time evolution of a three m condensate system on which we make measurements, which entangle the modes and so es relative phases between them. By establishing, in turn, the phases of two condensates relat a reference condensate, we show that the relative phase between them can be predicted acc The existence of such a phase standard gives a precise definition to the phase of a conde [S0031-9007(99)08970-X]
33 citations
TL;DR: In this paper, the authors investigate the spectrum and coherence of an atomic beam slowly coupled out of a trap containing partially condensed Bose gas at a finite temperature and show the existence of a remarkable process involving the simultaneous creation of an output atom and an elementary excitation inside the trap.
Abstract: We investigate the spectrum and coherence of an atomic beam slowly coupled out of an atomic trap which contains a partially condensed Bose gas at a finite temperature. The spectrum contains a coherent fraction emerging from the condensate and a thermal fraction emerging from the thermal excitations in the trap. We show the existence of a remarkable process involving the simultaneous creation of an output atom and an elementary excitation (quasiparticle) inside the trap. This process, which can serve as a probe to pair correlations in the condensate, can become dominant for a suitable choice of the coupling parameters. [S0031-9007(98)08353-7]
19 citations
TL;DR: In this paper, a theoretical and experimental study of the efficiency of adiabatic transfer between the Zeeman substates of the cesium ground level, using the $D1$ $F=\stackrel{\ensuremath{\rightarrow}}{4}{4}^{'}}$ transition is presented.
Abstract: We present a theoretical and experimental study of the efficiency of adiabatic transfer between the Zeeman substates of the cesium ground level, using the $D1$ $F=\stackrel{\ensuremath{\rightarrow}}{4}{4}^{\ensuremath{'}}$ transition. In order to understand the application of the adiabatic condition to such multistate systems, we examine the separation of their energy eigenstates as a function of the number of participating states. We present a systematic investigation of the physical factors affecting the efficiency of transfer in a multistate system and we see that velocity selection plays an important role in these calculations. We use the theory to compare the suitability of adiabatic transfer with $F=\stackrel{\ensuremath{\rightarrow}}{1}{1}^{\ensuremath{'}}$ and $F=\stackrel{\ensuremath{\rightarrow}}{4}{4}^{\ensuremath{'}}$ transitions for atom optics.
11 citations
TL;DR: In this paper, the effects of atomic interactions through dipole-dipole coupling and hard-core collisions have been analyzed and it was shown that for reasonable physical parameters the dipole interactions have little contribution to the atomic dynamics.
Abstract: It was proposed by two of us (Wiseman H M and Collett M J 1995 Phys. Lett. A 202 246) that a device producing a coherent atomic wave (that is, an atom laser) could be built using dark-state cooling of atoms in a trap. Here we present a more complete analysis of this system, including the effects of atomic interactions through dipole-dipole coupling and hard-core collisions. We show that for reasonable physical parameters the dipole interactions have little contribution to the atomic dynamics. In contrast, the hard-core collisions are likely to dominate the laser linewidth. In fact, it would appear necessary to select (or produce) a species with a hard-core scattering radius of much less than one nm in order for the output of the device to be phase coherent.
6 citations
15 May 1999-Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences
TL;DR: The validity range of the approximations being used to describe the ultracold interactions in the context of the interaction between caesium atoms at the temperatures produced by evaporation in a magnetic trap are examined.
Abstract: We describe the lowenergy scattering theory relevant to the description of the BoseEinstein condensed gases recently produced using evaporative cooling. We examine the validity range of the approxi...
4 citations
23 May 1999
TL;DR: In this paper, a numerical model based on the Gross-Pitaevskii equation (GPE) is presented that generates self-consistent thermally excited states and allows the process of evaporative cooling to be convincingly simulated.
Abstract: Summary form only given. Recent experimental demonstrations of Bose-Einstein condensation (BEC) in trapped dilute alkali gases provide a strong incentive for developing reliable theoretical models of the phenomenon. In this paper, a numerical model based on the Gross-Pitaevskii equation (GPE) is presented that generates self-consistent thermally excited states and allows the process of evaporative cooling to be convincingly simulated.
TL;DR: In this paper, a caesium atom interferometer using a combination of microwaves and momentum-changing adiabatic transfer pulses is described, which achieves spatial separation between the arms of interferometers.
Abstract: We describe in detail our caesium atom interferometer which uses a combination of microwaves and momentum-changing adiabatic transfer pulses. This combination allows us to achieve spatial separation between the arms of the interferometer. We account for the observed visibility of the resulting interference fringes and find that the effects which contribute the most are optical pumping and magnetic fields.
01 Jan 1999
TL;DR: In this paper, the temperature of the atomic ensemble is associated with the coherence length, which can be measured with an interferometer and used to deduce the temperature even at very low temperatures where time of flight methods fail.
Abstract: Atom interferometers provide a unique way in which to study atomic de Broglie waves1} and properties of atomic sources. One such property of the atomic ensemble, the temperature, is associated with the coherence length, which can be measured with an interferometer. This can be used to deduce the temperature even at very low temperatures where time of flight methods fail.
TL;DR: In this article, it was shown that a grey state becomes darker the more the atom is exposed to on-resonant light, which can be understood qualitatively in terms of the quantum Zeno effect.