We investigate, both experimentally and theoretically, the static geometric properties of a harmonically trapped Bose-Einstein condensate of 6 Li 2 molecules in laser speckle potentials. Experimentally, we measure the in situ column density profiles and the corresponding transverse cloud widths over many laser speckle realizations. We compare the measured widths with a theory that is non-perturbative with respect to the disorder and includes quantum fluctuations. Importantly, for small disorder strengths we find quantitative agreement with the perturbative approach of Huang and Meng, which is based on Bogoliubov theory. For strong disorder our theory perfectly reproduces the geometric mean of the measured transverse widths. However, we also observe a systematic deviation of the individual measured widths from the theoretically predicted ones. In fact, the measured cloud aspect ratio monotonously decreases with increasing disorder strength, while the theory yields a constant ratio. We attribute this discrepancy to the utilized local density approximation, whose possible failure for strong disorder suggests a potential future improvement.
Heat engines convert thermal energy into mechanical work both in the classical and quantum regimes. However, quantum theory offers genuine nonclassical forms of energy, different from heat, which so far have not been exploited in cyclic engines to produce useful work. We here experimentally realize a novel quantum many-body engine fuelled by the energy difference between fermionic and bosonic ensembles of ultracold particles that follows from the Pauli exclusion principle. We employ a harmonically trapped superfluid gas of 6 Li atoms close to a magnetic Feshbach resonance which allows us to effectively change the quantum statistics from Bose-Einstein to Fermi-Dirac. We replace the traditional heating and cooling strokes of a quantum Otto cycle by tuning the gas between a Bose-Einstein condensate of bosonic molecules and a unitary Fermi gas (and back) through a magnetic field. The quantum nature of such a Pauli engine is revealed by contrasting it to a classical thermal engine and to a purely interaction-driven device. We obtain a work output of several 10 6 vibrational quanta per cycle with an efficiency of up to 25%. Our findings establish quantum statistics as a useful thermodynamic resource for work production, shifting the paradigm of energy-conversion devices to a new class of emergent quantum engines.
We use ultracold bosonic gases in optical speckle potentials to study an open quantum system with spatiotemporal dynamics on a tunable time scale. For sufficiently slow disorder dynamics, we reveal the onset of dissipation due to the dynamical environment in thermal gases, while superfluidity shields the quantum gases from the noisy environment. For faster dynamics, we observe excitations in the superfluid, indicating an interaction-dependent dynamics of the excitations competing with the external dynamics of the environment. Our findings thereby establish a platform for systematically studying open-system dynamics with a controllable dynamic disorder and spatiotemporal noise with interactions in classical and quantum regimes.
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