The possibility of extracting energy from a system in a cyclic process is discussed. We present an explicit example where a system, initially prepared in a microcanonical state, is able to perform such an operation. The example is similar to the Szilard engine, but the microcanonical initial condition allows one to design a protocol where measurement is not necessary.

• Received 3 September 2009

DOI:https://doi.org/10.1103/PhysRevLett.104.245704