Room 117

Work extraction and thermodynamics for individual quantum systems

Avijit Misra

IMSc

Thermodynamics is traditionally concerned with systems
comprised of a large number of particles. Here we present a framework
for extending thermodynamics to individual quantum systems, including
explicitly a thermal bath and work-storage device (essentially a
‘weight’ that can be raised or lowered). We prove that the second law
of thermodynamics holds in our framework, and gives a simple protocol
to extract the optimal amount of work from the system, equal to its
change in free energy. Our results apply to any quantum system in an
arbitrary initial state, in particular including non-equilibrium
situations. The optimal protocol is essentially reversible, similar to
classical Carnot cycles, and indeed, we show that it can be used to
construct a quantum Carnot engine.

Paper reference: NATURE COMMUNICATIONS | 5:4185 | DOI: 10.1038/ncomms5185