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The spin on a silicon defect in diamond can be prepared in a coherent quantum state, a promising sign that it could encode information in a quantum internet.

The quantum internet of the future could take many forms, but its core components will be quantum bits (qubits) that can store information and qubits that can carry information [1, 2]. Atom-sized defects in diamond called silicon vacancy centers are promising candidates as the storage component: they possess a single spin whose quantum state (such as a superposition between “up” and “down”) could encode information. This stored information can also be precisely imprinted on the light the defects emit when excited optically. Independent research groups led by Fedor Jelezko at Ulm University in Germany [3] and by Mete Atatüre at Cambridge University in the UK [4] have now measured the coherence time
T∗2 of the spin on a negatively charged silicon vacancy (SiV) center, a key quantity determining how long the coherent superposition of up and down states can be maintained. Although the measured coherence time is only on the order of tens of nanoseconds (ns), a number of strategies exist to increase it to the point that SiV centers could be viable quantum internet components.

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