Wave chaos as signature for depletion of a Bose-Einstein condensate

We study the expansion of repulsively interacting Bose-Einstein condensates (BECs) in shallow one-dimensional potentials. We show for these systems that the onset of wave chaos in the Gross-Pitaevskii equation (GPE), i.e. the onset of exponential separation in Hilbert space of two nearby condensate wave functions, can be used as indication for the onset of depletion of the BEC and the occupation of excited modes within a many-body description. Comparison between the multiconfigurational time-dependent Hartree for bosons (MCTDHB) method and the GPE reveals a close correspondence between the many-body effect of depletion and the mean-field effect of wave chaos for a wide range of single-particle external potentials. In the regime of wave chaos the GPE fails to account for the fine-scale quantum fluctuations because many-body effects beyond the validity of the GPE are non-negligible. Surprisingly, despite the failure of the GPE to account for the depletion, coarse grained expectation values of the single-particle density such as the overall width of the atomic cloud agree very well with the many-body simulations. The time dependent depletion of the condensate could be investigated experimentally, e.g., via decay of coherence of the expanding atom cloud.Comment: 12 pages, 10 figure

Electron correlations in the antiproton energy-loss distribution in He

We present ab initio calculations of the electronic differential energy-transfer cross sections for antiprotons with energies between 3 keV and 1 MeV interacting with helium. By comparison with simulations employing the mean-field description based on the single-active electron approximation we are able to identify electron correlation effects in the stopping and straggling cross sections. Most remarkably, we find that straggling exceeds the celebrated Bohr straggling limit when correlated shake-up processes are included.The present paper was supported by Grants No. FWF-SFB049 (Nextlite), No. FWF-SFB041 (VICOM), No. WWTF MA14-002, Doctoral College Grant No. FWF-W1243 (Solids4Function), by the National Research, Development and Innovation Office (NKFIH) Grant No. KH 126886, and by the high performance computing resources of the Babeş-Bolyai University. J.F. acknowledges funding from the European Research Council under Grant No. ERC-2016-STG-714870 and by the Ministerio de Economía y Competitividad (Spain) through a Ramón y Cajal grant. X.- M.T. was supported by a Grants-in-Aid for Scientific Research (Grant No. JP16K05495) from the Japan Society for the Promotion of Scienc

Electron correlations in the antiproton energy-loss distribution in He

We present ab initio calculations of the electronic differential energy-transfer cross sections for antiprotons with energies between 3 keV and 1 MeV interacting with helium. By comparison with simulations employing the mean-field description based on the single-active electron approximation we are able to identify electron correlation effects in the stopping and straggling cross sections. Most remarkably, we find that straggling exceeds the celebrated Bohr straggling limit when correlated shake-up processes are included

Chaos-induced loss of coherence of a Bose-Einstein condensate

peer reviewedThe mean-field limit of a bosonic quantum many-body system is described by (mostly) nonlinear equations of motion which may exhibit chaos very much in the spirit of classical particle chaos, i.e., by an exponential separation of trajectories in Hilbert space with a rate given by a positive Lyapunov exponent λ. The question now is whether λ imprints itself onto measurable observables of the underlying quantum many-body system even at finite particle numbers. Using a Bose-Einstein condensate expanding in a shallow potential landscape as a paradigmatic example for a bosonic quantum many-body system, we show that the system loses its coherence at an exponentially fast rate. Furthermore, we show that the rate is given by the Lyapunov exponent associated with the chaotic mean-field dynamics. Finally, we demonstrate that this chaos-induced loss of coherence imprints itself onto the visibility of interference fringes in the total density after time of flight, thus, opening the possibility to measure λ and with it the interplay between chaos and nonequilibrium quantum matter in a real experiment