Deterministic Generation of a Cluster State of Entangled Photons

TL;DR

This paper demonstrates a method using semiconductor quantum dots to generate long, entangled photon strings in a cluster state, advancing quantum information processing capabilities.

Contribution

It introduces a deterministic scheme for creating long entangled photon strings using dark excitons in quantum dots, following a specific theoretical proposal.

Findings

Produced photon strings of a few hundred photons

Entanglement persists over 5 sequential photons

Full quantum process tomography performed

Abstract

We use semiconductor quantum dots, "artificial atoms," to implement a scheme for deterministic generation of long strings of entangled photons in a cluster state, an important resource for quantum information processing. We demonstrate a prototype device which produces strings of a few hundred photons in which the entanglement persists over 5 sequential photons. The implementation follows a proposal by Lindner and Rudolph (Phys. Rev. Lett. 2009) which suggested periodic timed excitation of a precessing electron spin as a mechanism for entangling the electron spin with the polarization of the sequentially emitted photons. In our realization, the entangling qubit is a quantum dot confined dark exciton. By performing full quantum process tomography, we obtain the process map which fully characterizes the evolution of the system, containing the dark exciton and n photons after n applications of the periodic excitations. Our implementation may greatly reduce the resources needed for quantum information processing.