Physics of Many-body Nonreciprocal Model: Quantum system with Maxwell's Pressure Demon.

In this letter, we show that nonreciprocal hopping in many-body systems can be identified as an effect of Maxwell's pressure demons, which provides a pressure gradient to the system at a steady state without changing the energy levels. From the demon's point of view, in the many-body Bosonic/Fermionic Hatano-Nelson model, there exist new physical phenomena compared with Hermitian counterparts without demons: Liouvillian Bose-Einstein condensation and Liouvillian Fermi-surface in real space. Our results will aid in investigating many-body physics of non-Hermitian quantum systems.