arXiv subjects

J. R. Anglin

Publications and source records attributed to J. R. Anglin.

At least 37 records · Page 2Linked to original sources

arXiv2001

How to be master of your domains

Prepare a two-species BEC in a perfectly phase-mixed state. By applying Rabi drives, one can tune the range of wavelengths of phase-separating excitations that are dynamically unstable. Yada yada yada, this determines the characteristic sizes of the eventual spin domains. The trapping potential is neglected because it makes life hard, but of course this is a terrible approximation, and the results are of only inspirational value. Since this is thus a rather trivial calculation, the very modest increase in kudos that might accrue from journal publication does not seem to outweigh the grief of having to change the title.

cond-mat.soft↗

arXiv2001

Local vortex nucleation and the surface mode spectrum of large condensates

A combination of analytical and numerical approaches obtains the complete dispersion curve for surface excitations in a condensate held in a plane linear potential. This improvement on previous approximate results yields an accurate formula for the local Landau critical velocity for vortex nucleation at the surface of a sufficiently large condensate, which agrees very well with recent experiments. The dispersion curve for surface modes at a hard wall potential is also presented, for contrast.

cond-mat.soft↗

arXiv2001

Dynamics of a two-mode Bose-Einstein condensate beyond mean-field theory

We study the dynamics of a two-mode Bose-Einstein condensate in the vicinity of a mean-field dynamical instability. Convergence to mean-field theory (MFT), with increasing total number of particles $N$, is shown to be logarithmically slow. Using a density matrix formalism rather than the conventional wavefunction methods, we derive an improved set of equations of motion for the mean-field plus the fluctuations, which goes beyond MFT and provides accurate predictions for the leading quantum corrections and the quantum break time. We show that the leading quantum corrections appear as decoherence of the reduced single-particle quantum state; we also compare this phenomenon to the effects of thermal noise. Using the rapid dephasing near an instability, we propose a method for the direct measurement of scattering lengths.

physics.atom-ph↗

arXiv2001

Quantum effects on the dynamics of a two-mode atom-molecule Bose-Einstein condensate

We study the system of coupled atomic and molecular condensates within the two-mode model and beyond mean-field theory (MFT). Large amplitude atom-molecule coherent oscillations are shown to be damped by the rapid growth of fluctuations near the dynamically unstable molecular mode. This result contradicts earlier predictions about the recovery of atom-molecule oscillations in the two-mode limit. The frequency of the damped oscillation is also shown to scale as $\sqrt{N}/\log N$ with the total number of atoms $N$, rather than the expected pure $\sqrt{N}$ scaling. Using a linearized model, we obtain analytical expressions for the initial depletion of the molecular condensate in the vicinity of the instability, and show that the important effect neglected by mean field theory is an initially non-exponential `spontaneous' dissociation into the atomic vacuum. Starting with a small population in the atomic mode, the initial dissociation rate is sensitive to the exact atomic amplitudes, with the fastest (super-exponential) rate observed for the entangled state, formed by spontaneous dissociation.

cond-mat↗

arXiv2001

Bose-Einstein condensates in traps of time-dependent topology

Superfluid phenomena can be explained in terms of the topologies of the order parameter and of the confining vessel. For example, currents in a toroidal vessel can be characterized by a discrete and conserved quantity, the winding number. In trapped Bose-Einstein condensates, the topology of the trap can be characterized by the topology of the Thomas-Fermi surface of its N-particle ground state. This can be altered during an experiment, so that a toroidal trap may deform into a more spherical shape, allowing an initially persistent current to decay into singly-quantized vortices. We investigate such a procedure numerically, and confirm that the Thomas-Fermi prescription for the trap topology gives an accurate picture of vortex formation.

cond-mat↗

arXiv2001

Creating vortex rings and three-dimensional skyrmions in Bose-Einstein condensates

We propose a method of generating a vortex ring in a Bose-Einstein condensate by means of electromagnetically-induced atomic transitions. Some remnant population of atoms in a second internal state remains within the toroidal trap formed by the mean field repulsion of the vortex ring. This population can be removed, or it can be made to flow around the torus (i.e. within the vortex ring). If this flow has unit topological winding number, the entire structure formed by the two condensates is an example of a three-dimensional skyrmion texture.

cond-mat.stat-mech↗

arXiv2001

Sonic black holes in dilute Bose-Einstein condensates

The sonic analog of a gravitational black hole in dilute-gas Bose-Einstein condensates is investigated. It is shown that there exist both dynamically stable and unstable configurations which, in the hydrodynamic limit, exhibit a behavior completely analogous to that of gravitational black holes. The dynamical instabilities involve creation of quasiparticle pairs in positive and negative energy states. We illustrate these features in two qualitatively different one-dimensional models, namely, a long, thin condensate with an outcoupler laser beam providing an ``atom sink,'' and a tight ring-shaped condensate. We have also simulated the creation of a stable sonic black hole by solving the Gross-Pitaevskii equation numerically for a condensate subject to a trapping potential which is adiabatically deformed. A sonic black hole could in this way be created experimentally with state-of-the-art or planned technology.

gr-qc↗

arXiv2000

Dark-Bright Solitons in Inhomogeneous Bose-Einstein Condensates

We investigate dark-bright vector solitary wave solutions to the coupled non-linear Schrödinger equations which describe an inhomogeneous two-species Bose-Einstein condensate. While these structures are well known in non-linear fiber optics, we show that spatial inhomogeneity strongly affects their motion, stability, and interaction, and that current technology suffices for their creation and control in ultracold trapped gases. The effects of controllably different interparticle scattering lengths, and stability against three-dimensional deformations, are also examined.

cond-mat↗

arXiv2000

Sonic analog of gravitational black holes in Bose-Einstein condensates

It is shown that, in dilute-gas Bose-Einstein condensates, there exist both dynamically stable and unstable configurations which, in the hydrodynamic limit, exhibit a behavior resembling that of gravitational black holes. The dynamical instabilities involve creation of quasiparticle pairs in positive and negative energy states, as in the well-known suggested mechanism for black hole evaporation. We propose a scheme to generate a stable sonic black hole in a ring trap.

gr-qc↗

arXiv2000

The Quantum Josephson Hamiltonian In The Phase Representation

The quantum Josephson Hamiltonian of two weakly linked Bose-Einstein condensates is written in an overcomplete phase representation, thus avoiding the problem of defining a Hermitian phase operator. We discuss the limit of validity of the standard, non-rigorous Mathieu equation, due to the onset of a higher order $\cos 2 ϕ$ term in the Josephson potential, and also to the overcompleteness of the representation (the phase $ϕ$ being the relative phase between the two condensates). We thereby unify the Boson Hubbard and Quantum Phase models.

cond-mat.stat-mech↗

arXiv2000

Dynamic splitting of a Bose-Einstein Condensate

We study the dynamic process of splitting a condensate by raising a potential barrier in the center of a harmonic trap. We use a two-mode model to describe the phase coherence between the two halves of the condensate. Furthermore, we explicitly consider the spatial dependence of the mode funtions, which varies depending on the potential barrier. This allows to get the tunneling coupling between the two wells and the on-site energy as a function of the barrier height. Moreover we can get some insight on the collective modes which are excited by raising the barrier. We describe the internal and external degrees of freedom by variational ansatz. We distinguish the possible regimes as a function of the characteristic parameters of the problem and identify the adiabaticity conditions.

cond-mat↗

arXiv2000

Motion of dark solitons in trapped Bose-Einstein condensates

We use a multiple time scale boundary layer theory to derive the equation of motion for a dark (or `grey') soliton propagating through an effectively one-dimensional cloud of Bose-Einstein condensate, assuming only that the background density and velocity vary slowly on the soliton scale. We show that solitons can exhibit viscous or radiative acceleration (anti-damping), which we estimate as slow but observable on experimental time scales.

cond-mat↗

arXiv2000

Probing quantum statistical mechanics with Bose gases: Non-trivial order parameter topology from a Bose-Einstein quench

This is a less technical presentation of the ideas in quant-ph/9804035 [Phys Rev Lett 83 (1999), 1707-1710]. A second order phase transition induced by a rapid quench can lock out topological defects with densities far exceeding their equilibrium expectation values. This phenomenon is a generic prediction of nonequilibrium statistical mechanics, and can appear in a wide range of physical systems. We discuss it qualitatively in the context of trapped dilute Bose-Einstein condensates, outline a simple quantitative theory based on the time-dependent Ginzburg-Landau equation, and briefly compare the results of quantum kinetic theory.

cond-mat.stat-mech↗

arXiv1998

Instabilities of wave function monopoles in Bose-Einstein condensates

We present analytic and numerical results for a class of monopole solutions to the two-component Gross-Pitaevski equation for a two-species Bose condensate in an effectively two-dimensional trap. We exhibit dynamical instabilities involving vortex production as one species pours through another, from which we conclude that the sub-optical sharpness of potentials exerted by matter waves makes condensates ideal tools for manipulating condensates. We also show that there are two equally valid but drastically different hydrodynamic descriptions of a two-component condensate, and illustrate how different phenomena may appear simpler in each.

cond-mat↗

arXiv1998

Mossbauer effect for dark solitons in Bose-Einstein condensates

We show that the energetic instability of dark solitons is associated with particle-like motion, and present a simple equation of motion, based on the Mössbauer effect, for dark solitons propagating in inhomogeneous Thomas-Fermi clouds. Numerical simulations support our theory. We discuss some experimental approaches.

cond-mat↗

arXiv1998

Inhibition of spontaneous emission in Fermi gases

Fermi inhibition is a quantum statistical analogue for the inhibition of spontaneous emission by an excited atom in a cavity. This is achieved when the relevant motional states are already occupied by a cloud of cold atoms in the internal ground state. We exhibit non-trivial effects at finite temperature and in anisotropic traps, and briefly consider a possible experimental realization.

cond-mat.stat-mech↗

arXiv1998

Winding up by a quench: vortices in the wake of rapid Bose-Einstein condensation

A second order phase transition induced by a rapid quench can lock out topological defects with densities far exceeding their equilibrium expectation values. We use quantum kinetic theory to show that this mechanism, originally postulated in the cosmological context, and analysed so far only on the mean field classical level, should allow spontaneous generation of vortex lines in trapped Bose-Einstein condensates of simple topology, or of winding number in toroidal condensates.

quant-ph↗

arXiv1996

A precision test of decoherence

The motion of a charged particle over a conducting plate is damped by Ohmic resistance to image currents. This interaction between the particle and the plate must also produce decoherence, which can be detected by examining interference patterns made by diffracted particle beams which have passed over the plate. Because the current densities within the plate decay rapidly with the height of the particle beam above it, the strength of decoherence should be adjustable across a wide range, allowing one to probe the full range of quantum through classical behaviour.

quant-ph↗