Hyperentanglement purification and concentration assisted by diamond NV centers inside photonic crystal cavities

TL;DR

This paper introduces novel protocols for hyperentanglement purification and concentration using NV centers in diamond within photonic crystal cavities, enabling improved quantum communication over long distances.

Contribution

It presents the first hyperentanglement purification protocol for mixed states with errors in two degrees of freedom, utilizing nonlinear optics of NV centers.

Findings

First hyperentanglement purification protocol for mixed states in two DOFs.

Efficient hyperentanglement concentration protocol with maximal success probability.

Protocols are useful for long-distance quantum communication.

Abstract

Hyperentanglement has attracted much attention for its fascinating applications in quantum communication. However, it is impossible to purify a pair of photon systems in a mixed hyperentangled state with errors in two degrees of freedom using linear optical elements only, far different from all the existing entanglement purification protocols in a degree of freedom (DOF) for quantum systems. Here, we investigate the possibility of purifying a spatial-polarization mixed hyperentangled Bell state with the errors in both the spatial mode and polarization DOFs, resorting to the nonlinear optics of a nitrogen-vacancy (NV) center in a diamond embedded in a photonic crystal cavity coupled to a waveguide. We present the first hyperentanglement purification protocol for purifying a pair of two-photon systems in a mixed hyperentangled Bell state with the errors in two DOFs. Besides, we propose an efficient hyperentanglement concentration protocol for a partially hyperentangled Bell pure state, which has the maximal success probability in principle. These two protocols are useful in long-distance quantum communication with hyperentanglement