Photonic graph state generation from quantum dots and color centers for quantum communications

Abstract

Highly entangled graph states of photons have applications in universal quantum computing and in quantum communications. In the latter context, they have been proposed as the key ingredient in the establishment of long-distance entanglement across quantum repeater networks. Recently, a general deterministic approach to generate repeater graph states from quantum emitters was given. However, a detailed protocol for the generation of such states from realistic systems is still needed in order to guide experiments. Here, we provide such explicit protocols for the generation of repeater graph states from two types of quantum emitters: NV centers in diamond and self-assembled quantum dots. A crucial element of our designs is an efficient controlled-Z gate between the emitter and a nuclear spin, used as an ancilla qubit. Additionally, a fast protocol for using pairs of exchange-coupled quantum dots to produce repeater graph states is described. Our focus is on near-term experiments feasible with existing experimental capabilities.