A Scheme for Performing Strong and Weak Sequential Measurements of Non-commuting Observables

TL;DR

This paper proposes a scheme for performing sequential measurements of non-Hermitian observables in quantum systems, enabling exploration of quantum paths and weak values that challenge classical intuition.

Contribution

It introduces a novel measurement scheme based on erasure protocols for sequentially measuring non-commuting, non-Hermitian observables in quantum systems.

Findings

Allows measurement of non-Hermitian operators

Enables weak and strong sequential measurements

Reveals complex quantum path behaviors

Abstract

Quantum systems usually travel a multitude of different paths when evolving through time from an initial to a final state. In general, the possible paths will depend on the future and past boundary conditions, as well as the system's dynamics. We present a gedanken experiment where a single system apparently follows mutually exclusive paths simultaneously, each with probability one, depending on which measurement was performed. This experiment involves the measurement of observables that do not correspond to Hermitian operators. Our main result is a scheme for measuring these operators. The scheme is based on the erasure protocol [Phys. Rev. Lett. 116, 070404 (2016), arXiv:1409.1575] and allows a wide range of sequential measurements at both the weak and strong limits. At the weak limit the back action of the measurement cannot be used to account for the surprising behavior and the resulting weak values provide a consistent yet strange account of the system's past.