Entanglement concentration of high-dimensional unknown partially entangled state

TL;DR

This paper presents a universal scheme for entanglement concentration of high-dimensional, unknown, partially entangled states using linear optics and cross-Kerr nonlinearities, enabling efficient distillation of maximally entangled states.

Contribution

It introduces a novel, practical protocol for high-dimensional entanglement concentration that works with unknown parameters and only requires local operations at one site.

Findings

A two-qutrit maximally entangled Bell state can be distilled.

The protocol works with unknown parameters using linear optical elements.

Linear optical high-dimensional ECPs with known parameters are also proposed.

Abstract

High-dimensional quantum systems offer a number of advantages in larger information capacity, stronger noise resiliency, higher improved efficiency and accuracy over the qubit systems. In quantum communication the maximally entangled states will inevitably become mixed states or less-entangled pure states by the channel noise during the practical transmission or storage. We propose a universal scheme to concentrate nonlocal high-dimensional generalized Bell states with unknown parameters. After the cross-Kerr nonlinearities, $X$-quadrature homodyne measurements, and single-partite projection measurements are performed only at Bob's site, a two-qutrit maximally entangled Bell state can be distilled, while previous entanglement concentration protocols (ECPs) mostly focused on two-level qubit systems. The concentrated partially entangled qubit states, reserved as the by-product are the fascinating resources for some quantum information processing tasks. Moreover, single-qutrit projection measurement, the key ingredient for our ECP with unknown parameters, are completed by using linear optical elements. Additionally, linear optical high-dimensional ECP with known parameters are also designed.