A quantum engine in the BEC–BCS crossover

Heat engines convert thermal energy into mechanical work both in the classical and quantum regimes^ 1 . However, quantum theory offers genuine non-classical forms of energy, different from heat, which so far have not been exploited in cyclic engines. Here we experimentally realize a quantum many-body engine fuelled by the energy difference between fermionic and bosonic ensembles of ultracold particles that follows from the Pauli exclusion principle^ 2 . We employ a harmonically trapped superfluid gas of ^6Li atoms close to a magnetic Feshbach resonance^ 3 that allows us to effectively change the quantum statistics from Bose–Einstein to Fermi–Dirac, by tuning the gas between a Bose–Einstein condensate of bosonic molecules and a unitary Fermi gas (and back) through a magnetic field^ 4 – 10 . The quantum nature of such a Pauli engine is revealed by contrasting it with an engine in the classical thermal regime and with 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. This study reports the creation of a model thermodynamic engine that is fuelled by the energy difference resulting from changing the statistics of a quantum gas from bosonic to fermionic.