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 nonunitary 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.
- Received 20 August 2021
- Accepted 7 July 2022
DOI:https://doi.org/10.1103/PhysRevX.12.031031
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
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 show that this apparent difficulty may be turned into a tool for driving an initially trivial system into a desired quantum many-body state simply by observing it.
Specifically, we present a procedure for which robust particle transport along the edge of a material with an insulating bulk can be induced solely through local particle density measurements. This is achieved by choosing the set of local measurements whose trajectory forms a closed loop in the bulk—as if we “stir” the system by switching our observation points.
A particularly appealing picture arises in the limit of rapid measurements—the quantum Zeno limit; namely, classical stochastic dynamics emerge. In this limit, we present a mathematical framework that allows for the direct calculation of the induced robust transport along the edge. Edge transport of this kind is a well-investigated phenomenon in a special class of materials known as Floquet topological insulators. We compare this phenomenon with our measurement-induced case, where some of the traditional tools associated with closed systems do not directly apply.
Our system serves as an example of the power of the fundamental principles of quantum mechanics to generate fascinating new physics.
