Reconsidering Photonic Quantum Heat Engine Efficiency

A device - referred to as a photonic quantum heat engine - was reported in Nature Photonics [J. Kim, S. Oh, D. Yang, J. Kim, M. Lee and K. An, A photonic quantum engine driven by superradiance, Nat. Photon. 16 (2022) 707-711] with an efficiency of 98 +/- 4%. Moreover, in a related News & Views contribution in the same issue [M. Kim, M. Scully and A. Svidzinsky, A supercharged photonic quantum heat engine, Nat. Photon. 16 (2022) 669-670], this device was reported to exceed the Carnot limit, an extraordinary claim. As Carl Sagan once remarked, "Extraordinary claims require extraordinary evidence. " Here, we outline the fundamental lack of empirical evidence that would be required to support such a claim, show that the actual efficiency of the device is 0% and bring to attention critical aspects of the operating physics of the device.