Using thermodynamics to identify quantum subsystems. (16th December 2017)

• Record Type: Journal Article
• Authors: Stokes, Adam; Deb, Prasenjit; Beige, Almut
• Is Part Of: Journal of modern optics. Volume 64(2017)Supplement 4
• Page Start: S7
• Page End: S19
• Publication Date: 2017-12-16
• Subjects: Quantum electrodynamics -- quantum thermodynamics -- anomalous heat flow; Optics -- Periodicals; 535
• DOI: 10.1080/09500340.2017.1295108
• Languages: English
• ISSNs: 0950-0340

Abstract

Abstract : There are many ways to decompose the Hilbert spaceH of a composite quantum system into tensor product subspaces. Different subsystem decompositions generally imply different interaction Hamiltonians V, and therefore different expectation values for subsystem observables. This means that the uniqueness of physical predictions is not guaranteed, despite the uniqueness of the total Hamiltonian H and the total Hilbert spaceH . Here we use Clausius' version of the second law of thermodynamics (CSL) and standard identifications of thermodynamic quantities to identify possible subsystem decompositions. It is shown that agreement with the CSL is obtained, whenever the total Hamiltonian and the subsystem-dependent interaction Hamiltonian commute (i.e.[ H, V ] = 0 ). Not imposing this constraint can result in the transfer of heat from a cooler to a hotter subsystem, in conflict with thermodynamics. We also investigate the status of the CSL with respect to non-standard definitions of thermodynamic quantities and quantum subsystems.