Thermodynamics of projective quantum measurements
Abstract
Quantum measurement of a system can change its mean energy as well as entropy. A selective measurement (classical or quantum) can be used as a ‘Maxwell's demon’ to power a singletemperature heat engine by decreasing the entropy. Quantum mechanically, so can a nonselective measurement, despite increasing the entropy of a thermal state. The maximal amount of work extractable following the measurement is given by the change in free energy: W^{(non)sel}_{max} = ∆E_{meas}  T_{Bath}∆S^{(non)sel}_{meas}. This follows from the ‘generalized 2nd law for nonequilibrium initial state’ (Hasegawa et al 2010 Phys. Lett. A 374 10014), an elementary reduction of which to the standard law is given here. It is shown that W^{sel}_{max}  W^{nonsel}_{max} is equal to the work required for resetting the memory of the measuring device and that no such resetting is needed in the nonselective case. Consequently, a singlebath engine powered by either kind of measurement works at a net loss of T_{Bath}∆S^{nonsel}_{meas} per cycle. By replacing the measurement by a reversible ‘premeasurement’ and allowing a work source to couple to the system and memory, the cycle can be rendered completely reversible.
 Publication:

Physica Scripta Volume T
 Pub Date:
 November 2012
 DOI:
 10.1088/00318949/2012/T151/014028
 Bibcode:
 2012PhST..151a4028E