### Quantum computer built inside a diamond

##### April 5, 2012

The first multi-qubit computer with protection against decoherence (noise that prevents the computer from functioning properly) has been developed by an international team of scientists.

The team’s diamond quantum computer system featured two quantum bits (“qubits”).

The team used the impurities in flaws in the diamond — the spin of a nitrogen nucleus as the first qubit and the spin of an electron from another flaw as the second qubit.

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, which is large, is much more stable but slower.

Solid-state multi-qubit computing systems have already been developed, but this was the first to incorporate decoherence protection — using microwave pulses to continually switch the direction of the electron spin rotation to protect the qubits from noise from the environment — the scientists said.

ADDED: It also operated at room temperature.

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” for quantum computing (find the correct choice in X/2 tries – if X is the number of total choices you have to search through). So, with four choices total, you’ll find the correct one after two tries on average.

The quantum 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.

The multinational team included USC, Delft University of Technology, Iowa State University, and the University of California, Santa Barbara.

Ref.: T. van der Sar, *et al.* Decoherence-protected quantum gates for a hybrid solid-state spin register.*Nature*, 2012; 484 (7392): 82 DOI: 10.1038/nature10900

ADDED: Quantum calculations rendered insensitive for disruptions