A heat engine converts thermal energy into mechanical energy. While macroscopic engines were the basis of the industrial revolution, scaling down heat engines to the smallest possible scale might be the key to investigate fundamental concepts at the boundaries between quantum mechanics and thermodynamics. Now, Johannes Roβnagel, Kilian Singer and colleagues from the University of Mainz and other institutions in Germany report the realization of a single-atom heat engine.
The atom (a40Ca+ ion) is confined along the axis of a conical electromagnetic trap. At the narrow end of the trap, an electric field noise generator acts as a hot reservoir. When the ion heats up, it moves towards a region of higher potential energy, against the restoring force of the trap, and thus producing work. At the wide end of the cone, a blue-detuned laser cools the ion, sending it back to the narrow end and thus setting up a closed thermodynamic cycle. With each oscillation, the work done by the atom accumulates and if left unchecked would result in increasingly larger and larger amplitudes. To keep the system under steady state, the authors use a second cooling laser as a damping mechanism. In this way, they can measure the energy associated with each oscillation.
The efficiency of the engine is around 0.3%, but in terms of power generated per mass of active material, the value — 1.5 kW kg−1 — is similar to that of a car engine.