LAUSR

We study universal aspects of fluctuations in an ensemble of noninteracting continuous quantum thermal machines in the steady-state limit, beyond linear response. Considering an individual machine, such as a refrigerator, in which relative fluctuations (and high order cumulants) of the cooling heat current to the absorbed heat current, η (n), are upper-bounded, η(n)⩽ηCn with n ⩾ 2 and η C the Carnot efficiency, we prove that an ensemble of N distinct machines similarly satisfies this upper bound on the relative fluctuations of the ensemble, ηN(n)⩽ηCn . For an ensemble of distinct quantum refrigerators with components operating in the tight-coupling limit we further prove the existence of a lower bound on ηN(n) in specific cases, exemplified on three-level quantum absorption refrigerators and resonant-energy thermoelectric junctions. Beyond special cases, the existence of a lower bound on ηN(2) for an ensemble of quantum refrigerators is demonstrated by numerical simulations. We further show that the lower bound on ηN(2) may, however, be violated for an ensemble of quantum engines.