Nondestructive verification of continuous-variable entanglement

TL;DR

This paper proposes a nondestructive optical method to verify bipartite entanglement in continuous-variable systems using beam-splitter and QND interactions, homodyne detection, and feedforward modulation, preserving the entanglement.

Contribution

It introduces a novel nondestructive entanglement verification technique based on QND interactions and homodyne detection, applicable to Gaussian modes.

Findings

The method effectively verifies entanglement without destroying it.

Classical information from homodyne detection suffices for verification.

Added noise impacts the output entanglement in Gaussian modes.

Abstract

An optical procedure in the context of continuous variables to verify bipartite entanglement without destroying both systems and their entanglement is proposed. To perform the nondestructive verification of entanglement, the method relies on beam-splitter and quantum nondemolition (QND) interactions of the signal modes with two ancillary probe modes. The probe modes are measured by homodyne detections, and the obtained information is used to feed forward modulation of signal modes, concluding the procedure. Characterizing the method by figures of merit used in QND processes, we can establish the conditions for an effectively quantum scheme. Based on such conditions, it is shown that the classical information acquired from the homodyne detections of probe modes is sufficient to verify the entanglement of the output signal modes. The processing impact due to added noise on the output entanglement is assessed in the case of Gaussian modes.