Efficient single-photon-assisted entanglement concentration for partially entangled photon pairs

TL;DR

This paper introduces two efficient entanglement concentration protocols for partially entangled photon pairs, using linear optics and cross-Kerr nonlinearities, which are practical, do not require precise initial state knowledge, and are suitable for multi-photon systems.

Contribution

The paper proposes two novel entanglement concentration protocols that are more practical, economical, and suitable for multi-photon systems compared to existing methods.

Findings

Both protocols successfully concentrate entanglement with higher efficiency.

They do not require knowledge of initial state coefficients.

The methods are feasible with current technology and improve long-distance quantum communication.

Abstract

We present two realistic entanglement concentration protocols (ECPs) for pure partially entangled photons. A partially entangled photon pair can be concentrated to a maximally entangled pair with only an ancillary single photon in a certain probability, while the conventional ones require two copies of partially entangled pairs at least. Our first protocol is implemented with linear optics and the second one is implemented with cross-Kerr nonlinearities. Compared with other ECPs, they do not need to know the accurate coefficients of the initial state. With linear optics, it is feasible with current experiment. With cross-Kerr nonlinearities, it does not require the sophisticated single-photon detectors and can be repeated to get a higher success probability. Moreover, the second protocol can get the higher entanglement transformation efficiency and it maybe the most economical one by far. Meanwhile, both of protocols are more suitable for multi-photon system concentration, because they need less operations and classical communications. All these advantages make two protocols be useful in current long-distance quantum communications.