Characterizing mixed state entanglement through single-photon interference

TL;DR

This paper introduces a novel method to verify and measure entanglement in bipartite mixed states using single-photon interference patterns, eliminating the need for coincidence detection.

Contribution

It demonstrates how to determine entanglement in mixed states through single-photon interference, bypassing traditional coincidence measurement methods.

Findings

Entanglement can be verified without detecting both photons.

Interference pattern visibility encodes entanglement information.

Method applicable to two-photon mixed states from identical sources.

Abstract

Entanglement verification and measurement is essential for experimental tests of quantum mechanics and also for quantum communication and information science. Standard methods of verifying entanglement in a bipartite mixed state require detection of both particles and involve coincidence measurement. We present a method that enables us to verify and measure entanglement in a two-photon mixed state without detecting one of the photons, i.e., without performing any coincidence measurement or postselection. We consider two identical sources, each of which can generate the same two-photon mixed state but they never emit simultaneously. We show that one can produce a set of single-photon interference patterns, which contain information about entanglement in the two-photon mixed state. We prove that it is possible to retrieve the information about entanglement from the visibility of the interference patterns. Our method reveals a distinct avenue for verifying and measuring entanglement in mixed states.