Reservoir engineering for maximally efficient quantum engines

Abstract

We employ reservoir engineering technique to build an artificial thermal bath at arbitrary (effective) negative and positive temperatures for a single spin system. The required interaction engineering is achieved by applying a specific sequence of radio-frequency pulses using nuclear magnetic resonance, while the temperature of the bath can be controlled by appropriate preparation of the initial ^{1}H nuclear spin state. This artificial reservoir allowed us to implement a single qubit quantum engine that operates at a single reservoir at effective negative temperature and with maximum efficiency, independent of the unitary transformation performed on the qubit system, as long as it changes the qubit state. We measured the population of the carbon spin and the efficiency of our quantum engine, which are in very good agreement with the predicted results.