A photonic quantum engine driven by superradiance

Making statistics work: a quantum engine in the BEC-BCS crossover

“…The novel Pauli stroke B→C, associated with the Pauli energy change E P 2 , replaces the traditional heating by a bath with the change of quantum statistics. All the strokes are unitary (apart from minor particle losses, see below) and, therefore, the entropy of the system is constant throughout the cycle, in contrast to conventional quantum heat engines [3][4][5][6][7][8]. The quantum gas can be analyzed at every instance along the cycle by taking in-situ absorption images in the optic-magnetic trap [20].…”

“…From a microscopic point of view, work in quantum systems is related to a displacement of energy levels and heat to a modification of their population's probability distribution [2]. Quantum heat engines realized so far convert thermal energy into mechanical work by cyclically operating between effective thermal reservoirs at different temperatures [3][4][5][6][7][8] like their classical counterparts, where heating/cooling strokes redistribute the quantum state populations. However, owing to the existence of distinct particle (Fermi or Bose) statistics, the level occupation probabilities of quantum many-body systems may strongly differ at the same temperature [1].…”

“…This step leads to the exchange of Pauli energy instead of heat. We emphasize that all strokes are unitary, preserving the entropy of the system throughout the cycle, in contrast to conventional quantum heat engines [3][4][5][6][7][8]. We measure atom numbers and cloud radii from in-situ absorption images [20], from which we determine the energy of the gas after each stroke of the engine.…”

Reconsidering Photonic Quantum Heat Engine Efficiency

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A device -referred to as a photonic quantum heat engine -was reported in Nature Photonics [1] with an efficiency of 98 ± 4%. Moreover, in a related News & Views contribution in the same issue [2], this device was reported to exceed the Carnot limit, an extraordinary claim.

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“…1a in Ref. [1], with additional description in the supplementary information associated with Ref. [1], consists of the following components: a beam of 138 Ba atoms, a tunable pump laser that is used to excite the atomic beam so that photons are emitted, a Fabry-Pérot cavity in which the mirrors act as a piston, a nanohole array aperture that serves to facilitate quantum coherent superradiance when the pump laser and mirror cavity are resonant (whereas when the pump laser frequency is detuned from the cavity resonance the photon emission is incoherent), and a piezoelectric transducer driven by an external voltage to move the "piston" (i.e., modulate the distance between the two mirrors).…”