Researchers at MIT may have just cracked one of the biggest challenges in their path to building a quantum computer.

The concept of quantum superposition refers to the ability of ‘qubits’, the atomic-scale building blocks of quantum computers, to inhabit multiple physical states at once. Qubits are able to perform computations at orders of magnitude faster than regular ‘bits’, which means a quantum computer would be vastly superior to even the fastest supercomputers available today.

But one of the challenges researchers need to overcome in quantum computing is stability. In most fields, stability can be accomplished via feedback control, by measuring the current state and making adjustments to keep the system at its desired state. But in the quantum world, taking those measurements destroys superposition, thus rendering quantum computing impossible.

Now, MIT’s researchers may have just hit on something. They’ve created a new kind of feedback control system for maintaining quantum superposition that uses synthetic diamonds and eliminates the need to take measurements. The system relies on what’s called the “nitrogen-vacancy center” within a diamond.

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

Here’s a very simplified explanation of what Cappellaro’s team have done:

Pure diamonds consist of carbon atoms that are arranged in a regular structure. Now, if a carbon nucleus goes missing from the lattice (where one would normally exist) that is considered a “vacancy”. Now, if a nitrogen atom is swapped out for a carbon atom that exists adjacent to that vacancy, what we have now is a “nitrogen-vacancy (NV) center”. When that NV center is subjected to a strong magnetic field, its electronic spin can be up, down or a quantum superposition of both.

That itself is the true value of quantum computing.

In their tests, Cappellaro’s team emitted microwaves that put the NV center’s electronic spin into superposition. Later, they use radio-frequency radiation to put the nitrogen nucleus into a spin state. This is followed by a second dose of low-powered microwaves that have the effect of entangling the spins of the nitrogen nucleus and the NV center, so that they become dependent on each other. It’s at this point that an NV qubit can be put to work as part of a quantum computer.

MIT’s research shows that diamonds can keep an NV-center quantum bit in superposition for up to 1,000 times longer than previously possible, bringing us another step closer to the goal of building a working quantum computer.

Image credit: geralt via pixabay