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Quantum researchers control qubit with light

Diamonds are a girl's quantum computer's best friend

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As the hunt continues for ways to manipulate qubits in solid state devices, UC Santa Barbara researchers have demonstrated using a laser to manipulate a qubit in diamond.

The qubit in question is actually considered a defect in a diamond's crystalline structure: it's called a “nitrogen-vacancy centre”, in which a nitrogen atom takes the place of a carbon atom, creating an adjacent vacancy. The properties of such vacancies, particularly photoluminescence, have been of interest to researchers for a long time.

Diamond NV centre qubit manipulation has been demonstrated before, but using microwaves rather than optics. Microwaves, however, don't focus as well as light, so in using an optical read-write mechanism, the researchers say they've demonstrated a system that could address individual qubits in an array.

In the UC work, the researchers treated the nitrogen-vacancy centre as a qubit, and found that using only optical processes, they were able to both control and read the spin state. As lead author of a paper at PNAS Christopher Yale explains:

“The initial problem we were trying to solve was to figure out a way that we could place our qubit into any possible superposition of its state in a single step.

“It turns out that in addition to being able to do that just by adjusting the laser light interacting with our spin, we discovered that we could generate coherent rotations of that spin state and read out its state relative to any other state of our choosing using only optical processes.”

Diamonds are difficult to grow, so the researchers hope that similar room-temperature qubits will be feasible in other materials. ®

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