Silicon vacancy centers as diamond quantum network nodes

Short answer: The negatively charged silicon vacancy center in diamond is a candidate node for quantum repeaters, because its electron spin can act as a memory linked to photons, but connecting that spin efficiently to optical fibre is a major obstacle. A 2023 Communications Physics paper couples silicon vacancy centers in a nanodiamond to a microcavity and reports spin initialization within 67 ns at 80% fidelity, and a 2021 Journal of Applied Physics perspective reviews diamond color centers for quantum networks. These are laboratory results and a review.

Why color centers

The 2023 abstract says large-scale quantum communication networks need quantum repeaters because of signal attenuation in optical fibres. Ideal repeater nodes efficiently link a quantum memory with photons serving as flying qubits, and color centers in diamond, particularly the silicon vacancy center, are promising candidates. It names inefficient connection between the color center's spin and optical fibre networks as a major obstacle that optical resonators could resolve.

2023: a microcavity experiment

The authors couple individual silicon vacancy centers in a nanodiamond to a hemispherical, stable Fabry-Perot microcavity, achieving Purcell factors larger than 1. They demonstrate coherent optical driving between ground and excited state with a Rabi frequency of 330 MHz, and all-optical initialization and readout of the electron spin in magnetic fields up to 3.2 T. They report spin initialization within 67 ns at 80% fidelity and a spin lifetime of 350 ns. They say the demonstration opens the way to quantum repeater applications, which is a statement about direction, and the 350 ns lifetime is short for a memory.

2021: a review

The Journal of Applied Physics perspective says large-scale quantum networks will enable applications from quantum communications to distributed sensing, metrology and computing. It reviews requirements for network nodes and color centers in diamond as node candidates, gives an overview of state-of-the-art network experiments with them, and discusses future directions with a focus on qubit control and coherence for distributing and storing entangled states and on efficient spin-photon interfaces. It also discusses a route toward large-scale integrated devices that combine color centers with other photonic materials.

A 2019 nanophotonic interface paper

A 2019 Physical Review Letters paper is titled "Quantum Network Nodes Based on Diamond Qubits with an Efficient Nanophotonic Interface". Only its title was available when this post was written, so its results are not described here.

Limits

The 2023 result is a single-device demonstration with figures that the authors themselves frame as a step toward repeaters. The review is a perspective, not a new measurement. Neither reports a working repeater link.

FAQ

Why silicon vacancy centers?

The 2023 abstract calls diamond color centers, particularly the negatively charged silicon vacancy, promising candidates for repeater nodes.

What is the main obstacle?

Inefficient connection between the spin and optical fibre networks, per the 2023 paper, which uses a microcavity to address it.

What were the headline numbers?

Spin initialization within 67 ns at 80% fidelity, a 350 ns spin lifetime, and a Rabi frequency of 330 MHz.

Is this a working quantum repeater?

No. The authors say it opens the way to repeater applications.

Where can I read an overview?

The 2021 Journal of Applied Physics perspective reviews diamond color centers for quantum networks.