Experimental Observation of Topological Quantum Criticality

TL;DR

This paper experimentally observes quantum criticality at the transition between topological Anderson insulator phases in a photonic quantum walk, highlighting the role of quantum coherence in topological phase transitions.

Contribution

It provides the first experimental evidence of topological quantum criticality in a photonic system, using spin-dependent quantum walks to detect critical behavior.

Findings

Detection of topological Anderson criticality via spin-susceptibility profiles

Quantum coherence is essential for observing the critical signal

Controlled decoherence removes the criticality signature

Abstract

We report on the observation of quantum criticality forming at the transition point between topological Anderson insulator phases in a one-dimensional photonic quantum walk with spin. The walker's probability distribution reveals a time-staggered profile of the dynamical spin-susceptibility, recently suggested as a smoking gun signature for topological Anderson criticality in the chiral symmetry class AIII. Controlled breaking of phase coherence removes the signal, revealing its origin in quantum coherence.