Higher winding number in a non-unitary photonic quantum walk

TL;DR

This paper demonstrates the experimental realization of large winding numbers in a non-unitary photonic quantum walk, revealing topological phase transitions and enriching understanding of non-unitary topological phenomena.

Contribution

It introduces a method to observe high winding numbers in non-unitary quantum walks using partial measurements and loss in photonics, expanding topological studies to non-unitary regimes.

Findings

Winding numbers of three and four detected in non-unitary quantum walks.

Topological phase transitions identified via statistical moments.

Pseudo-unitary breaking observed near phase boundaries.

Abstract

Topological matter exhibits exotic properties yet phases characterized by large topological invariants are difficult to implement, despite rapid experimental progress. A promising route toward higher topological invariants is via engineered Floquet systems, particularly in photonics, where flexible control holds the potential of extending the study of conventional topological matter to novel regimes. Here we implement a one-dimensional photonic quantum walk to explore large winding numbers. By introducing partial measurements and hence loss into the system, we detect winding numbers of three and four in multi-step non-unitary quantum walks, which agree well with theoretical predictions. Moreover, by probing statistical moments of the walker, we identify locations of topological phase transitions in the system, and reveal the breaking of pseudo-unitary near topological phase boundaries. As the winding numbers are associated with non-unitary time evolution, our investigation enriches understanding of topological phenomena in non-unitary settings.