The dynamics and steady state properties of an ensemble of non-interacting spins change significantly according to the type of coupling with a bath. We compare the situation where the spins interact with a common bath, also referred to as collective bath coupling, with the situation where each spin interacts with an independent bath, referred to as independent couplings. The observed differences in the spins’ dynamics suggest that it could have some impacts in operations using thermal baths, like thermal machines and thermometry.

Focusing first on Otto engines, we show that collective coupling with a common bath can lead to a two-fold increase in the output power. The first increase is related to altered steady state properties of the spin ensemble (when compared to interaction with independent bath). The second is based on the accelerated equilibration induced by the common bath. This second increase in the output power is not present in continuous thermal machines.

In a second time, we analyse the performances of temperature estimation of a thermal bath using an ensemble of spins. We find that collective coupling can result in higher precision of the temperature estimation, especially at high temperature, reaching even the Heisenberg scaling—inversely proportional to the number of spins.