Synthetic diamond will enable quantum networks

Princeton University researchers are using synthetic diamonds to help create a quantum communication network.

Quantum information networks could be extremely secure and could also allow new quantum computers to work together to solve currently unsolvable problems. The main problem has been to preserve fragile quantum information over long distances.

Researcher were able to store and transmit bits of quantum information, known as qubits, using a diamond in which they had replaced two carbon atoms with one silicon atom.

Synthetic diamonds could serve as quantum repeaters for networks based on qubits.

The team produced neutral silicon vacancies in diamonds.

Science – Observation of an environmentally insensitive solid-state spin defect in diamond

The neutral silicon vacancy is good at both transmitting quantum information using photons and storing quantum information using electrons, which are key ingredients in creating the essential quantum property known as entanglement, which describes how pairs of particles stay correlated even if they become separated. Entanglement is the key to quantum information’s security: recipients can compare measurements of their entangled pair to see if an eavesdropper has corrupted one of the messages.

The next step in the research is to build an interface between the neutral silicon vacancy and the photonic circuits to bring the photons from the network into and out of the color center.

In search of the right diamond defect

Certain defects in diamond are among the most promising physical implementations of qubits, the building blocks of quantum computers. However, identifying a defect with balanced properties is tricky: Nitrogen vacancy centers have a long lifetime but comparatively poor optical properties, whereas negatively charged silicon vacancy centers have the opposite characteristics. Rose et al. used careful materials engineering to stabilize the neutral charge state of silicon vacancy centers and found that they combine long coherence times with excellent optical properties.

Abstract

Engineering coherent systems is a central goal of quantum science. Color centers in diamond are a promising approach, with the potential to combine the coherence of atoms with the scalability of a solid-state platform. We report a color center that shows insensitivity to environmental decoherence caused by phonons and electric field noise: the neutral charge state of silicon vacancy (SiV0). Through careful materials engineering, we achieved >80% conversion of implanted silicon to SiV0. SiV0 exhibits spin-lattice relaxation times approaching 1 minute and coherence times approaching 1 second. Its optical properties are very favorable, with ~90% of its emission into the zero-phonon line and near–transform-limited optical linewidths. These combined properties make SiV0 a promising defect for quantum network applications.

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