Reversing Quantum Nondemolition Interaction as Quantum Erasing

TL;DR

This paper demonstrates a method to reverse quantum nondemolition interactions in continuous variables by measurement and feedforward, effectively erasing information leakage and restoring the original quantum state.

Contribution

It introduces a quantum eraser protocol for CV systems that reverses QND interactions using homodyne measurement and feedforward, restoring quantum coherence.

Findings

Successful restoration of quantum states demonstrated with coherent and squeezed states.

Experimental verification via Wigner functions and fidelity measurements.

Trade-off observed between information leakage and coherence restoration.

Abstract

We reverse a quantum nondemolition (QND) interaction and restore the signal quantum state by measurement and feedforward. This operation corresponds to quantum erasing for continuous variables (CVs). CV quantum eraser restores the coherence of the signal quantum state by erasing the signal information leaking to another system, where the information leaking is induced by the QND interaction. We employ a homodyne measurement for erasing of the information. Then, by performing a feedforward displacement operation, we restore the initial quantum state together with its coherence. For verification, we use a coherent state and a squeezed vacuum state as inputs, and then restore one of them or the other, whichever we choose. Experimental results are shown as Wigner functions, average fidelity, change in coherence, and trade-off between leakage information and coherence.