Scalable spin\u2013photon entanglement by time-to-polarization conversion

Rui Vasconcelos,Philip Walther,Sarah Reisenbauer,Daniel Wirtitsch,Georg Wachter,Michael Trupke,Cameron Salter,Jörg Schmiedmayer

doi:10.1038/s41534-019-0236-x

Abstract

The realization of quantum networks and quantum computers relies on the scalable generation of entanglement, for which spin-photon interfaces are strong candidates. Current proposals to produce entangled-photon states with such platforms place stringent requirements on the physical properties of the photon emitters, limiting the range and performance of suitable physical systems. We propose a scalable protocol, which significantly reduces the constraints on the emitter. We use only a single optical transition and an asymmetric polarizing interferometer. This device converts the entanglement from the experimentally robust time basis via a path degree of freedom into a polarization basis, where quantum logic operations can be performed. The fundamental unit of the proposed protocol is realized experimentally in this work, using a nitrogen-vacancy center in diamond. This classically assisted protocol greatly widens the set of physical systems suited for scalable entangled-photon generation and enables performance enhancement of existing platforms.

Highlights

The generation of entangled-photon states is of central importance in linear optical quantum computing (LOQC)[1,2] and optical quantum communication,[3,4] and has potential applications in quantum sensing and metrology.[5]
A first demonstration of the cluster-state machine gun” (CSMG) protocol with quantum dots was shown by Schwartz et al.[13], where the length of the cluster-state was limited to three photons due to the short lifetime of the qubit
In this work we develop and demonstrate an alternative, scalable scheme based on time-to-polarization conversion (TPC)

Summary

Introduction

The generation of entangled-photon states is of central importance in linear optical quantum computing (LOQC)[1,2] and optical quantum communication,[3,4] and has potential applications in quantum sensing and metrology.[5]. Cluster states are desirable resources as they enable measurement-based quantum computation and have an in-built resilience to noise and loss.[7,8,9] Spin-based protocols have been developed for the generation of entangled-photon strings, the most prominent of these being the “cluster-state machine gun” (CSMG) of Lindner and Rudolph.[10] This protocol is appealingly simple and robust, and can be scaled to higher-dimensional cluster states using multiple spins.[11,12] Its requirements are quite stringent. A first demonstration of the CSMG protocol with quantum dots was shown by Schwartz et al.[13], where the length of the cluster-state was limited to three photons due to the short lifetime of the qubit

Methods

Results

Conclusion