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Defining work in quantum mechanics: interfering trajectories and decohering heat baths

October 26, 2015 - 11:00am
Christopher Jarzynski

The question of how to define the work performed on a quantum system undergoing a thermodynamic process has recently received much attention, particularly in the context of nonequilibrium work relations.  For closed quantum systems evolving under time-dependent Hamiltonians, a plausible definition of quantum work is provided by the "two-point measurement" (TPM) protocol, involving projective measurements of the initial and final Hamiltonian.  In the first part of my talk, I will show that under this definition the statistical distribution of quantum work values can be understood in terms of classical trajectories that interfere coherently, via path-integral phases, and I will extend this result to describe tunneling into the classically forbidden region.  

The second part of the talk concerns the work performed on a quantum system in the presence of a decohering environment, where the system-environment coupling is sufficient to bring about decoherence but too weak to allow for substantial energy exchange between system and environment.  I will argue that in this situation the TPM protocol again provides a natural definition of quantum work, and I will show that nonequilibrium work relations remain valid within this scheme.

2115 Computer and Space Sciences
College Park, MD 20742