Quantum Matter Seminar

Monitored quantum criticality — Nishimori physics and beyond

Constant-depth quantum circuits with mid-circuits measurements can efficiently prepare long-range entanglement structures, including topological quantum order as it has long been established in the toric code. In this talk, I will discuss novel types of quantum criticality that can arise from such shallow circuits and which are generally described by (2+0)-dimensional non-unitary conformal field theories. Nishimori universality has emerged as a seemingly ubiquitous fixed point for such critical theories, which we discuss for mixed-state transitions arising from weak measurement or incoherent noise (or both). Putting Nishimori physics in competition to other critical theories, such as percolation, self-dual (Kramers-Wannier) quantum criticality or a novel tricritical theory at the intersection of phases with strong, weak or broken Z_2 symmetry, RG flows between these critical theories can be established and embedded in rich phase diagrams, potentially amenable to experimental exploration on current quantum platforms. Finally, we make connections to classical statistical physics and learning transitions in Bayesian inference, its connection to Born's rule and correlated disorder models of 1-replica theories.