Reversing the weak quantum measurement for a photonic qubit

TLDR

The study demonstrates conditional reversal of a weak quantum measurement on a photonic qubit and investigates information gain and the reversal’s role as information erasure. The experiment uses linear optics to perform a weak quantum measurement that induces a nonunitary qubit transformation, followed by a reversal operation that restores the original state upon success. Conditional reversal of the weak measurement was achieved with a state‑recovery fidelity exceeding 94 % for partial‑collapse strengths up to 0.9, as confirmed by quantum process tomography.

Abstract

We demonstrate the conditional reversal of a weak (partial-collapse) quantum measurement on a photonic qubit. The weak quantum measurement causes a nonunitary transformation of a qubit which is subsequently reversed to the original state after a successful reversing operation. Both the weak measurement and the reversal operation are implemented linear optically. The state recovery fidelity, determined by quantum process tomography, is shown to be over 94% for partial-collapse strength up to 0.9. We also experimentally study information gain due to the weak measurement and discuss the role of the reversing operation as an information erasure.