While today’s fibre-optic networks distribute classical information across global length scales, the quantum networks of the not-so-distant tomorrow will exploit the exotic properties of entanglement and superposition to securely transmit quantum information between end-users at the same global scale. This capability will enable quantum-encrypted communications for all manner of organizations – from governments and banks to healthcare providers and the military – and open the way, inevitably, to the implementation of at-scale parallel quantum computing resources, with remote computing nodes linked quantum mechanically across the network.
Though still under development, quantum repeaters represent a core enabling technology as the quantum internet comes into view, serving a similar function as fibre amplifiers in classical optical networks by correcting for the loss and infidelity that occur as quantum information propagates over long distances (though without disrupting the quantum state of light as it passes through the network).
Quantum repeaters operate by transferring information encoded on photons onto a stationary memory qubit where the information can be stored and corrected. Defect qubits, such as colour centres in synthetic diamond, are shaping up as credible candidates for this task because they have an effective interface with light (the source of their colour) and because these defects can have a long-lived “spin” memory. Two classes of diamond-defect qubits are the focus of intense R&D interest in this regard: the nitrogen-vacancy spin centre (NV) and the silicon-vacancy spin centre (SiV), both of which are formed by removing two adjacent carbon atoms from a synthetic diamond crystal lattice and replacing them with a single nitrogen or silicon atom, respectively.
Here Bart Machielse, senior quantum research scientist at the AWS Center for Quantum Networking, tells Physics World how his team is accessing the leading-edge materials science and fabrication capabilities of research partner Element Six to realize “quantum advantage” in optical communications systems using synthetic diamond.
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