Edgy Labs Called it: Diamond-defect Qubits for Commercial Quantum Computers

A collaboration between MIT, Harvard, and Sandia National Laboratories created methodologies for diamond-vacancy-based quantum computing storage devices. 

In November of last year, we covered the exploits of City University of New York scientists, who were lasering data into diamond nitrogen vacancies. We thrilled you with the prospect of carrying all of your life’s data–photos, videos, theses, and love letters–inside your wedding ring.

Now, the nanometer-scale atomic defects in diamonds can be used to encode qubits–or the basic unit of quantum data.

How long before diamonds are powering commercialized quantum computers? Given the scope of this study, we think it will be sooner rather than later.

Targeting Diamond-defect Qubits

In a May 26th Nature Communications article, MIT, Sandia, and Harvard scientists demonstrated “maskless creation of atom-like single silicon vacancy (SiV) centres in diamond nanostructures via focused ion beam implantation with ∼32 nm lateral precision and <50 nm positioning accuracy relative to a nanocavity.”

Or, in other words, the team very accurately targeted defects (in this case, silicon vacancies) in a diamond’s structure to create quantum emitters.

In the past, nitrogen vacancies have been the target of scientists looking to encode information into the surface of diamonds.

Vacancies in the lattice surface of diamonds are locations where there should be a carbon atom but there is not.

Dopants are atoms of other elements that fill the carbon vacancy.

Where these two meet, a dopant-vacancy center, free electrons are available. The magnetic orientation of these electrons can be in superposition, which, in practice, becomes the qubit.

Quantum computing is still largely hypothetical, and a big problem with it is the difficulty with reading information contained in qubits.

Diamond vacancies are an ideal solution as they serve as natural light emitters. Photons emitted by diamond vacancies can even maintain qubit superposition, enabling them to transfer quantum data between computers.

Silicon Instead of Nitrogen

As we mentioned, nitrogen vacancies are the most studied type of diamond defect. They are known to hold superposition longer than other diamond-defect qubits. Yet, nitrogen vacancies emit a wide range of light spectrum which can lead to inaccuracies in quantum computing measurement.

The MIT, Sandia, and Harvard team instead targeted silicon-vacancy centers which emit a very narrow band of light. Silicon diamond-defect qubits do not hold superposition very well, but the team suggests that cooling the vacancies down to the milikelvin range (nearly absolute zero) could help.

Creating the Vacancy

Where before scientists had taken advantage of existing vacancies in the diamond’s surface, this team developed multiple methods for creating vacancies and then filling them with silicon ions.

The MIT and Harvard team, after blasting the diamond’s surface with electrons to create additional vacancies, even heated the surface to 1,000 degrees Celsius in order to encourage bonding of the silicon ions with the vacancy center.

Why is this done?

In order to read information from the light-emitting qubits, they have to be amplified. In order to do this, as well as to redirect and combine them to perform quantum computations, the defects have to be precisely located.

For this reason, it’s easier and more efficient to create optical circuits in diamonds by etching defects in specific locations than to try and map optical circuits over random defect locations.

Dirk Englund, an associate professor leading the MIT team said, “The dream scenario in quantum information processing is to make an optical circuit to shuttle photonic qubits and then position a quantum memory wherever you need it. We’re almost there with this. These emitters are almost perfect.“