Local and nonlocal stochastic control of quantum chaos: Measurement- and control-induced criticality

TL;DR

This paper explores how local and global stochastic control influence quantum phase transitions, revealing that the nature and universality class of these transitions depend on the control's locality, with implications for quantum chaos and entanglement.

Contribution

It generalizes the control map to include local and global actions, demonstrating their distinct effects on quantum phase transitions and identifying a new universality class for global control.

Findings

Global control causes the two phase transitions to coincide.

Local control results in a known universality class similar to feedback-free models.

Global control leads to a novel universality class with exponent approximately 0.7.

Abstract

We theoretically study the topology of the phase diagram of a family of quantum models inspired by the classical Bernoulli map under stochastic control. The quantum models inherit a control-induced phase transition from the classical model and also manifest an entanglement phase transition intrinsic to the quantum setting. This measurement-induced phase transition has been shown in various settings to either coincide or split off from the control transition, but a systematic understanding of the necessary and sufficient conditions for the two transitions to coincide in this case has so far been lacking. In this work, we generalize the control map to allow for either local or global control action. While this does not affect the classical aspects of the control transition that is described by a random walk, it significantly influences the quantum dynamics, leading to the universality class of the measurement-induced transition being dependent on the locality of the control operation. In the presence of a global control map, the two transitions coincide and the control-induced phase transition dominates the measurement-induced phase transition. Contrarily, the two transitions split in the presence of the local control map or additional projective measurements and generically take on distinct universality classes. For local control, the measurement-induced phase transition recovers the Haar logarithmic conformal field theory universality class found in feedback-free models. However, for global control, a novel universality class with correlation length exponent $\nu \approx 0.7$ emerges from the interplay of control and projective measurements. This work provides a more refined understanding of the relationship between the control- and measurement-induced phase transitions.