Frontiers of quantum physics

Abstract:

We derive a general informationtheoretic equality for a system undergoing two projective measurements separated by a general temporal evolution. The equality implies the non-negativity of the mutual information between the measurement outcomes of the earlier and later projective measurements. We show that it also contains the Jarzynski relation between the average exponential of the thermodynamical work and the exponential of the difference between the initial and final free energy. Our result elucidates the informationtheoretic underpinning of thermodynamics and explains why the Jarzynski relation holds identically both quantumly as well as classically. © 2012 IOP Publishing Ltd.