Universal entangler with photon pairs in arbitrary states

TL;DR

This paper introduces a universal optical setup capable of transforming any arbitrary photon pair state into a Bell state with high success probability, utilizing linear optics, weak nonlinearities, and photon detection.

Contribution

It presents a novel scheme for near-deterministic entanglement transformation from arbitrary mixed states to Bell states using linear optics and weak nonlinearities.

Findings

Achieves near-deterministic Bell state conversion for arbitrary photon pairs.

Success probability reaches 0.5 with simple threshold detectors.

Discusses decoherence effects due to photon absorption losses.

Abstract

We propose a setup that transforms a photon pair in arbitrary rank-four mixed state, which could also be unknown, to a Bell state. The setup involves two linear optical circuits processing the individual photons and a parity gate working with weak cross-Kerr nonlinearity. By the photon number resolving detection on one of the output quantum bus or communication beams, the setup will realize a near deterministic transformation to a Bell state for every entangling attempt. With the simple threshold detectors, on the other hand, the system can still reach a considerable success probability of 0.5 per try. The decoherence effect caused by photon absorption losses in the operation is also discussed.