Solid-state quantum computer protects against decoherence

Researchers in the US and the Netherlands have moved closer to the next generation of electronics by building a quantum computer inside a diamond.

Quantum computers represent a potential way to create much smaller and faster devices than current digital technology but can suffer from a kind of signal noise called decoherence.

The scientists from the University of Southern California (USC), Iowa State University, the University of California Santa Barbara and Delft University of Technology have developed the first solid-state quantum computer that protects against decoherence.

They claim that their research, published today in the journal Nature, shows the viability of solid-state quantum computers, which can be more easily scaled up than earlier gas- and liquid-state systems.

The team used subatomic particles from impurities in the diamond to create the quantum bits (qubits) used to store data — in this case a nitrogen nucleus and a rogue electron — and used microwaves to protect them from decoherence.

While traditional computer bits can be set to one or zero, qubits can encode both states at the same time. This property, known as superposition, should allow quantum computers to one day perform calculations much faster than traditional computers.

Data is stored based on the spin of the subatomic particles, and as they spin they can gain inconsistencies in their motion. Electrons are smaller than nuclei and perform computations much more quickly, but more quickly experience decoherence.

‘A nucleus has a long decoherence time — in the milliseconds. You can think of it as very sluggish,’ said Prof Daniel Lidar, one of the USC researchers.

The scientists used microwave pulses to continually switch the direction of the electron spin rotation, reversing the inconsistencies in the particle’s motion and moving the qubit back to its original position, thereby protecting it against decoherence.

The research was funded by the National Science Foundation and the US Army Research Office’s Multidisciplinary University Research Initiative.