Fulfilling entanglement's optimal advantage via converting correlation to coherence

Abstract

Entanglement boosts performance limits in sensing and communication, and surprisingly the advantage over classical protocols can be even larger in presence of entanglement-breaking noise. However, to maximally fulfill such advantages requires an optimal measurement design, a challenging task as information is encoded in the feeble quantum correlation after entanglement is destroyed by loss and noise. For this reason, the optimal measurement design is still elusive for various entanglement-enhanced protocols long after their debut. We propose a conversion module to capture and transform the quantum correlation to coherent quadrature displacement, which enables the optimal receiver design for a wide range of entanglement-enhanced protocols, including quantum illumination, phase estimation, classical communication, and arbitrary thermal-loss channel pattern classification. Via heterodyne and passive linear optics, the conversion module maps the multi-mode quantum detection problem to the semi-classical detection problem of a single-mode noisy coherent state, so that explicit measurements can be constructed to achieve the optimal performance. Our module provides a paradigm of processing noisy quantum correlations for near-term implementation.