Entanglement, coherence, and redistribution of quantum resources in double spontaneous downconversion processes

TL;DR

This paper analyzes the quantum correlations, entanglement, and resource redistribution in tripartite Gaussian states generated by double spontaneous downconversion, with implications for quantum optics and circuit QED.

Contribution

It provides a complete analytical description of multipartite entanglement and coherence redistribution in bi-squeezed states from double downconversion processes.

Findings

The state exhibits genuine tripartite entanglement.

Homodyne detection converts coherence into entanglement.

Results have applications in quantum optics and circuit QED.

Abstract

We study the properties of bi-squeezed tripartite Gaussian states created by two spontaneous parametric down-conversion processes that share a common idler. We give a complete description of the quantum correlations across of all partitions, as well as of the genuine multipartite entanglement, obtaining analytical expressions for most of the quantities of interest. We find that the state contains genuine tripartite entanglement, in addition to the bipartite entanglement among the modes that are directly squeezed. We also investigate the effect of homodyne detection of the photons in the common idler mode, and analyse the final reduced state of the remaining two signal modes. We find that this measurement leads to a conversion of the coherence of the two signal modes into entanglement, a phenomenon that can be regarded as a redistribution of quantum resources between the modes. The applications of these results to quantum optics and circuit quantum electrodynamics platforms are also discussed.