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Superfluidity and critical velocities in nonequilibrium Bose-Einstein condensates
Michiel Wouters1, Iacopo Carusotto
1Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Physical Review Letters
|September 28, 2010
Summary
We studied superfluidity in exciton-polariton Bose-Einstein condensates. A sharp velocity threshold was found for drag force and density fringes, explained by excitation dispersion and Landau criterion.
Area of Science:
- Quantum physics
- Condensed matter physics
- Semiconductor physics
Background:
- Bose-Einstein condensates (BECs) exhibit superfluidity, a state with zero viscosity.
- Exciton-polaritons are quasiparticles formed from the coupling of excitons and photons in semiconductor microcavities.
- Nonequilibrium condensates, driven by continuous pumping and decay, present unique challenges to understanding superfluidity.
Purpose of the Study:
- To theoretically investigate the superfluid properties of a nonequilibrium Bose-Einstein condensate of exciton-polaritons.
- To analyze the behavior of supercurrents and the onset of dissipation in such systems.
- To develop a theoretical framework explaining observed phenomena based on fundamental principles.
Main Methods:
- Mean-field theory using a generalized Gross-Pitaevskii equation to describe condensate dynamics.
- Analysis of the drag force experienced by a moving object within the condensate.
- Investigation of density profile changes and the emergence of fringes.
- Development of a generalized Landau criterion based on elementary excitation dispersion.
Main Results:
- A sharp threshold in drag force and density fringe onset was identified as a function of velocity.
- The generalized Landau criterion successfully explains this threshold behavior by considering the excitation spectrum.
- Metastability of supercurrents in multiply-connected geometries was observed to persist at higher flow speeds than typically expected.
Conclusions:
- Nonequilibrium exciton-polariton condensates exhibit distinct superfluid properties governed by a generalized Landau criterion.
- The findings provide insights into the fundamental mechanisms limiting supercurrents and the onset of dissipation in quantum systems.
- The study highlights the potential for robust supercurrents in engineered quantum fluids.
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