Tuning the universality class of phase transitions by feedback: Open quantum systems beyond dissipation

TL;DR

This paper demonstrates that feedback control can be used to tune the universality class of phase transitions in open quantum systems, affecting their critical exponents and quantum fluctuations.

Contribution

It introduces a novel approach to control phase transition universality classes through feedback, extending previous models and considering both linearized and nonlinear spin ensemble models.

Findings

Feedback enables tuning of critical exponents in quantum phase transitions.

Quantum fluctuations near critical points can be controlled by feedback shape.

The approach applies to models beyond adiabatic light field elimination.

Abstract

We shift the paradigm of feedback control from the control of quantum states to the control of phase transitions in quantum systems. We show that feedback allows tuning the universality class of phase transitions via modifying its critical exponent. We expand our previous treatment [D. A. Ivanov, T. Yu. Ivanova, S. F. Caballero-Benitez, and I. B. Mekhov, Phys. Rev. Lett. 124, 010603 (2020)] of Dicke model and go beyond the approximation of adiabatically eliminated light field. Both linearized and nonlinear models of spin ensembles are considered. The tunability of quantum fluctuations near the critical point by the feedbacks of nontrivial shapes is explained by considering the fluctuation spectra and the system behavior at single quantum trajectories.