A quantum computer created inside a diamond is the first of its kind to include protection against ‘decoherence’ – noise that prevents it from functioning properly.
The team used the diamond’s impurities to create the computer’s two qubits. The spin in a rogue nitrogen nucleus became the first qubit, with an electron in a second flaw forming the second.
Electrons are smaller than nuclei and perform computations much more quickly, but also fall victim more quickly to decoherence. A qubit based on a nucleus is much more stable, but slower.
“A nucleus has a long decoherence time – in the milliseconds. You can think of it as very sluggish,” says University of Southern California professor Daniel Lidar.
Though solid-state computing systems have existed before, this is the first to incorporate decoherence protection – using microwave pulses to continually switch the direction of the electron spin rotation.
The team was able to demonstrate that their diamond-encased system does indeed operate in a quantum fashion by seeing how closely it matched Grover’s algorithm – a test consisting of a search of an unsorted database.
Because a quantum computer has the advantage of superposition, it can find the correct answer more quickly. While a standard search would get the right answer half the time, a quantum computer searching through an unsorted list of four choices will find the correct choice on the first try, every time.
Though not perfect, the new computer picked the correct choice on the first try about 95 percent of the time – enough to demonstrate that it operates in a quantum fashion, says the team.