Activity-induced quantum phase transitions

Unique phase transitions such as flocking and motility-induced phase separation (MIPS) have been intensely studied in classical active matter systems. It is interesting to ask how we can extend the concept of active matter to quantum systems. In this talk, we propose a quantum model that undergoes activity-induced phase transitions [1]. By using the correspondence between a classical stochastic model and a quantum Hamiltonian, we show that activity appears as non-Hermiticity in the quantum model, and describe how it can induce quantum analogues of flocking, MIPS, and microphase separation. We also find that such quantum phase transitions are equivalent to dynamical phase transitions in a biased classical stochastic system, which have recently been studied in classical models (e.g., [2]). Our results bridge the gap between two fast-developing areas: active matter and non-Hermitian quantum physics.

[1] K. Adachi, K. Takasan, and K. Kawaguchi, arXiv:2008.00996.
[2] L. Tociu, É. Fodor, T. Nemoto, and S. Vaikuntanathan, Phys. Rev. X 9, 041026 (2019).