Stirring by Staring: Measurement Induced Chirality

TL;DR

This paper demonstrates how repeated quantum measurements can induce chiral edge transport in a fermionic system, turning the observer's disturbance into a tool for creating topological phases with protected transport.

Contribution

It introduces a novel measurement-based method to generate chiral edge states in quantum systems, distinct from traditional driving techniques.

Findings

Measurement frequency controls the transition from classical to quantum transport.

In the Zeno limit, the system exhibits protected, classical stochastic dynamics.

Reducing measurement frequency diminishes charge flow, vanishing without measurements.

Abstract

In quantum mechanics, the observer necessarily plays an active role in the dynamics of the system, making it difficult to probe a system without disturbing it. Here, we leverage this apparent difficulty as a tool for driving an initially trivial system into a chiral phase. In particular, we show that by utilizing a pattern of repeated occupation measurements we can produce chiral edge transport of fermions hopping on a Lieb lattice. The procedure is similar in spirit to the use of periodic driving to induce chiral edge transport in Floquet topological insulators, while also exhibiting novel phenomena due to the non-unitary nature of the quantum measurements. We study in detail the dependence of the procedure on measurement frequency, showing that in the Zeno limit the system can be described by a classical stochastic dynamics, yielding protected transport. As the frequency of measurements is reduced, the charge flow is reduced and vanishes when no measurements are done.