Efficient polarization entanglement purification based on parametric down-conversion sources with cross-Kerr nonlinearity

TL;DR

This paper introduces an efficient entanglement purification protocol using parametric down-conversion sources and cross-Kerr nonlinearities, achieving high yield without complex linear optical gates or advanced detectors.

Contribution

It proposes a novel two-step entanglement purification method leveraging QND detectors and cross-Kerr nonlinearities, improving practicality and efficiency over existing techniques.

Findings

High purification yield achieved.

No need for linear optical CNot gates.

Compatible with practical quantum communication setups.

Abstract

We present a way for entanglement purification based on two parametric down-conversion (PDC) sources with cross-Kerr nonlinearities. It is comprised of two processes. The first one is a primary entanglement purification protocol for PDC sources with nondestructive quantum nondemolition (QND) detectors by transferring the spatial entanglement of photon pairs to their polarization. In this time, the QND detectors act as the role of controlled-not (CNot) gates. Also they can distinguish the photon number of the spatial modes, which provides a good way for the next process to purify the entanglement of the photon pairs kept more. In the second process for entanglement purification, new QND detectors are designed to act as the role of CNot gates. This protocol has the advantage of high yield and it requires neither CNot gates based on linear optical elements nor sophisticated single-photon detectors, which makes it more convenient in practical applications.