Virtual qubits, virtual temperatures, and the foundations of thermodynamics

Research output: Contribution to journalArticle (Academic Journal)peer-review

122 Citations (Scopus)


We argue that thermal machines can be understood from the perspective of "virtual qubits" at "virtual temperatures": The relevant way to view the two heat baths which drive a thermal machine is as a composite system. Virtual qubits are two-level subsystems of this composite, and their virtual temperatures can take on any value, positive or negative. Thermal machines act upon an external system by placing it in thermal contact with a well-selected range of virtual qubits and temperatures. We demonstrate these claims by studying the smallest thermal machines. We show further that this perspective provides a powerful way to view thermodynamics, by analyzing a number of phenomena. This includes approaching Carnot efficiency (where we find that all machines do so essentially by becoming equivalent to the smallest thermal machines), entropy production in irreversible machines, and a way to view work in terms of negative temperature and population inversion. Moreover we introduce the idea of "genuine" thermal machines and are led to considering the concept of "strength" of work.

Original languageEnglish
Article number051117
Pages (from-to)-
Number of pages14
JournalPhysical Review E: Statistical, Nonlinear, and Soft Matter Physics
Issue number5
Publication statusPublished - 14 May 2012


Dive into the research topics of 'Virtual qubits, virtual temperatures, and the foundations of thermodynamics'. Together they form a unique fingerprint.

Cite this