Single ion heat engine with maximum efficiency at maximum power
  We propose an experimental scheme to realize a nano heat engine with a single ion. An Otto cycle may be implemented by confining the ion in a linear Paul trap with tapered geometry and coupling it to engineered laser reservoirs. The quantum efficiency at maximum power is analytically determined in various regimes. Moreover, Monte Carlo simulations of the engine are performed that demonstrate its feasibility and its ability to operate at maximum efficiency of 30% under realistic conditions. 
Obinna Abah, Johannes Rossnagel, Georg Jacob, Sebastian Deffner,   Ferdinand Schmidt-Kaler, Kilian Singer, Eric Lutz
quant-ph cond-mat.mes-hall cond-mat.stat-mech