Scientists build quantum computer in a diamond

Diamonds are forever in the movies, and now they are making a stab at eternity in quantum computing.

An international group of scientists have built a working quantum computer inside a diamond, and for the first time, have included protection against decoherence.

According to a paper published in the April 5 issue of Nature, the team exploited natural flaws in diamond’s crystal structure to create quantum bits (the analogue of bits in a normal computer, but with the ability to encode both 1 and 0 at the same time). The problem is that this so-called state of superposition is not stable, and tends to collapse down to a more traditional classical state very easily. This is known as decoherence, and is to be avoided at all costs in quantum computing, as itintroduces noise and errors, making calculations less reliable.

Using solid state, such as diamond, helps a little anyway, since the spin of a nucleus is mroe stable than that of an electron.

"A nucleus has a long decoherence time – in the milliseconds. You can think of it as very sluggish," said Professor Daniel Lidar, who holds a joint appointment with the USC Viterbi School of Engineering and the USC Dornsife College of Letters, Arts and Sciences. Electrons are much faster, but much more easily disrupted.

The researchers used microwave pulses to continually switch the direction of the electron spin rotation, a trick which protects the system against decoherence. "It's a little like time travel," Lidar said, because switching the direction of rotation time-reverses the inconsistencies in motion as the qubits move back to their original position.

The computer was not large – even by quantum standards – consisting of just two qubits - but the proof of concept is important. Scaling up gaseous and liquid quantum systems is hard, the researchers say, while solid state looks more promising in this respect.

The work is published here.