Characterizing Symmetry-Protected Thermal Equilibrium by Work Extraction

Yosuke Mitsuhashi, Kazuya Kaneko, and Takahiro Sagawa

With the recent progress in quantum control techniques, theoretical research for novel quantum devices is getting increasingly important. For the investigation of energetic properties of such quantum devices, quantum thermodynamics has been intensively studied. While symmetry frequently appears in physics, how quantum thermodynamics is extended by introducing symmetries has remained an important open question.
In this work, we have completely identified the representation of thermal equilibrium in the presence of symmetries in a mathematically rigorous way, based on the second law of thermodynamics stating that work extraction is impossible from thermal equilibrium. Under symmetries, work extraction becomes more difficult, and thus more states behave as thermal equilibrium, referred to as symmetry-protected thermal equilibrium. Our result is applicable to situations unique to quantum mechanics, and would lead to more flexible design principles of quantum heat engines using symmetric systems.
This work was published online in the science journal Physical Review X on 18th April 2022.

Physical Review X: