Not Just Girls' Best Friend: Diamonds May Also Accelerate Quantum Computing


Superposition has troubled scientists for years, but researchers from the Massachusetts Institute of Technology (MIT) proposed a new method using synthetic diamonds.

The so-called "qubits" are central to quantum computing's success. These are the quantum computer's atomic-scale building blocks that enable the manifestation of not just one physical state at the same time. Commonly called "superposition," this is the principle that gives quantum computers their vast potential.

Maintaining stability is one of the most challenging parts of quantum computing. But researchers found a new tactic using synthetic diamonds. When perfected, the method can finally create quantum computers.

Feedback control often helps achieve stability. Using a specific state of mind, scientists can measure the existing state and tweak accordingly to make the system stable and retain it. However, this conventional process disrupts superposition in quantum computing.

The new approach used a diamond's nitrogen-vacancy center. This enabled the researchers to create a new feedback control system that doesn't require measurements to maintain quantum superposition.

"Instead of having a classical controller to implement the feedback, we now use a quantum controller. Because the controller is quantum, I don't need to do a measurement to know what's going on," said Paola Cappellaro, MIT's nuclear science and engineering associate professor.

A pure diamond contains carbon atoms that are structurally arranged in a regular pattern. A vacancy happens when a lattice doesn't have a carbon nucleus. A diamond with a nitrogen-vacancy (NV) center is one in which the carbon nucleus is replaced with a nitrogen atom.

When the researchers subjected a synthetic diamond to a robust magnetic field, the electronic spin of its NV center could be down, up or a quantum superposition of both states. In here lies quantum computing's real value.

First, microwaves are used to put the NV center's electronic spin into superposition. A radio-frequency radiation is then used to coax the nitrogen nucleus into a definite spin state.

Low-powered microwaves then "entangle" the rotations of both the NV center and its nitrogen nucleus so they will be reliant on one another. This creates the NV qubit that can work with other NV qubits to make a computation.

In essence, this synthetic diamond technique enabled an NV-center qubit to retain its superposition approximately 1,000 times as long. While diamonds are a girl's best friend, they too can be a quantum scientist's greatest ally.

The scientists' proposal on how to take our relationship to quantum computing to a whole new level was detailed on the journal Nature on April 7.

Photo: Michelle Tribe | Flickr

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