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Register a new userCharacterization of nonequilibrium states of trapped Bose-Einstein condensates
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Generation of different nonequilibrium states in trapped Bose-Einstein condensates is studied by numerically solving nonlinear Schrodinger equation. Inducing nonequilibrium states by shaking the trap, the following states are created: weak nonequilibrium, the state of vortex germs, the state of vortex rings, the state of straight vortex lines, the state of deformed vortices, vortex turbulence, grain turbulence, and wave turbulence. A characterization of nonequilibrium states is advanced by introducing effective temperature, Fresnel number, and Mach number.
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We numerically investigate low-energy stationary states of pseudospin-1 Bose-Einstein condensates in the presence of Rashba-Dresselhaus-type spin-orbit coupling. We show that for experimentally feasible parameters and strong spin-orbit coupling, the ground state is a square vortex lattice irrespective of the nature of the spin-dependent interactions. For weak spin-orbit coupling, the lowest-energy state may host a single vortex. Furthermore, we analytically derive constraints that explain why certain stationary states do not emerge as ground states. Importantly, we show that the distinct stationary states can be observed experimentally by standard time-of-flight spinindependent absorption imaging.
In this work we present numerical study of a trapped Bose-Einstein condensate perturbed by an alternating potential. The relevant physical situation has been recently realized in experiment, where the trapped condensate of $^{87}$Rb, being strongly perturbed, exhibits the set of spatial structures. Firstly, regular vortices are detected. Further, increasing either the excitation amplitude or modulation time results in the transition to quantum vortex turbulence, followed by a granular state. Numerical simulation of the nonequilibrium Bose-condensed system is based on the solution of the time-dependent 3D nonlinear Schr{o}dinger equation within the static and dynamical algorithms. The damped gradient step and time split-step Fourier transform methods are employed. We demonstrate that computer simulations qualitatively reproduce the experimental picture, and describe well the main experimental observables.
We report on the creation of three-vortex clusters in a $^{87}Rb$ Bose-Einstein condensate by oscillatory excitation of the condensate. This procedure can create vortices of both circulation, so that we are able to create several types of vortex clusters using the same mechanism. The three-vortex configurations are dominated by two types, namely, an equilateral-triangle arrangement and a linear arrangement. We interpret these most stable configurations respectively as three vortices with the same circulation, and as a vortex-antivortex-vortex cluster. The linear configurations are very likely the first experimental signatures of predicted stationary vortex clusters.
We experimentally demonstrate a multi-mode interferometer comprising a Bose-Einstein condensate of $^{39}$K atoms trapped in a harmonic potential, where the interatomic interaction can be cancelled exploiting Feshbach resonances. Kapitza-Dirac diffraction from an optical lattice coherently splits the BEC in multiple momentum components equally spaced that form different interferometric paths, closed by the trapping harmonic potential. We investigate two different interferometric schemes, where the recombination pulse is applied after a full or half oscillation in the confining potential. We find that the relative amplitudes of the momentum components at the interferometer output are sensitive to external forces, through the induced displacement of the harmonic potential with respect to the optical lattice. We show how to calibrate the interferometer, fully characterize its output and discuss perspective improvements.
Interferometry with ultracold atoms promises the possibility of ultraprecise and ultrasensitive measurements in many fields of physics, and is the basis of our most precise atomic clocks. Key to a high sensitivity is the possibility to achieve long measurement times and precise readout. Ultra cold atoms can be precisely manipulated at the quantum level, held for very long times in traps, and would therefore be an ideal setting for interferometry. In this paper we discuss how the non-linearities from atom-atom interactions on one hand allow to efficiently produce squeezed states for enhanced readout, but on the other hand result in phase diffusion which limits the phase accumulation time. We find that low dimensional geometries are favorable, with two-dimensional (2D) settings giving the smallest contribution of phase diffusion caused by atom-atom interactions. Even for time sequences generated by optimal control the achievable minimal detectable interaction energy $Delta E^{rm min}$ is on the order of 0.001 times the chemical potential of the BEC in the trap. From there we have to conclude that for more precise measurements with atom interferometers more sophisticated strategies, or turning off the interaction induced dephasing during the phase accumulation stage, will be necessary.
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