Detecting topological invariants in nonunitary discrete-time quantum walks

TL;DR

This paper demonstrates the experimental detection of topological invariants in nonunitary quantum walks using single photons, revealing quantized displacement and edge states, and confirming robustness against disorder.

Contribution

It introduces a method to measure topological invariants in nonunitary quantum walks via photon loss monitoring, advancing experimental topological physics.

Findings

Quantized average displacement indicates topological invariants.

Localized edge states confirm topological boundary properties.

Topological features are robust against disorder.

Abstract

We report the experimental detection of bulk topological invariants in nonunitary discrete-time quantum walks with single photons. The nonunitarity of the quantum dynamics is enforced by periodically performing partial measurements on the polarization of the walker photon, which effectively introduces loss to the dynamics. The topological invariant of the nonunitary quantum walk is manifested in the quantized average displacement of the walker, which is probed by monitoring the photon loss. We confirm the topological properties of the system by observing localized edge states at the boundary of regions with different topological invariants. We further demonstrate the robustness of both the topological properties and the measurement scheme of the topological invariants against disorder.