Motion from Measurement: The Role of Symmetry of Quantum Measurements

TL;DR

This paper explores how the symmetries of quantum measurements influence the emergence and magnitude of measurement-induced currents, highlighting the roles of inversion and time-reversal symmetry breaking.

Contribution

It classifies behaviors of measurement-induced currents based on symmetry considerations and analyzes their dependence on measurement rate and system coupling.

Findings

Breaking inversion symmetry induces currents.

Breaking time-reversal symmetry amplifies currents.

Currents exhibit non-monotonic dependence on measurement rate.

Abstract

In quantum mechanics, measurements are dynamical processes and thus they should be capable of inducing currents. The symmetries of the Hamiltonian and measurement operator provide an organizing principle for understanding the conditions for such currents to emerge. The central role is played by the inversion and time-reversal symmetries. We classify the distinct behaviors that emerge from single and repeated measurements, with and without coupling to a dissipative bath. While the breaking of inversion symmetry alone is sufficient to generate currents through measurements, the breaking of time-reversal symmetry by the measurement operator leads to a dramatic increase in the magnitude of the currents. We consider the dependence on the measurement rate and find that the current is non-monotonic. Furthermore, nondegenerate measurements can lead to current loops within the steady state even in the Zeno limit.