Thermodynamics requires a system to equilibrate with its thermal environment, alias a bath. However, our results over the years have shown that, surprisingly, nonintrusive observations of a quantum system may heat or cool it, thus preventing the equilibration [1,2]. Recently, we have shown that also the bath state, which is considered immutable in thermodynamics, is dramatically changed by a quantum probe and its observations [3]. These effects stem from the unavoidable entanglement between quantum systems and baths even when they are weakly coupled, thus undermining the tenets of thermodynamics in the quantum domain. Most remarkably, we have recently demonstrated that probe observations can render thermal bath states nearly pure [4]. The implications are far reaching, most prominently the ability to reverse the time arrow of the entire system-bath compound, by causing its quantum coherent oscillation. This raises the question: Is thermodynamics, which rests on the concept of a bath, compatible with quantum mechanics? It may appear necessary to assume that a quantum working medium in a heat machine is dissipated by a bath [5,6]. Yet, most recently, we have shown that heat machines can be perfectly coherent, non-dissipative devices realized by nonlinear interferometers fed by few thermal modes [7], so that baths are redundant. Finally, I will discuss the ability of observers to commute information to work [8] and speculate on the role of observers in physics [9].
References to our work
1. Nature 452, 724 (2008).
2. PRL 105,160401 (2010).
3. NJP 22, 083035 (2020).
4. Arxiv 2108.09826 (2021)
5. Nat. Commun. 9, 165 (2018).
6. PNAS 115, 9941 (2018); PNAS 114, 12156 (2017).
7. Arxiv2108.10157 (2021).
8. PRL 127, 040602 (2021).
9. G.Kurizki and G. Gordon, “The Quantum Matrix” (Oxford Univ. Press, 2020).
