- 2 September 2005 -

Silicon qubit overtakes GaAs

A silicon quantum-dot charged 'qubit' device has emerged from a team at Hitachi's Cambridge Laboratory at University of Cambridge, UK. The team comprises Dr. David Williams from the Hitachi Cambridge Laboratory, UK and Drs John Gorman and David Hasko of the University of Cambridge, UK and is based on many years of work on single-electron devices.

This is claimed to be the first step in the development of a quantum computer based on conventional silicon technology. Quantum computers make use of qubits, which can exist for a limited time as simultaneously a mixture of both 0 and 1 simultaneously and are subject to quantum entanglement, behaving as one system, so that the state of one qubit depends directly on the others.

This meaning that the potential processing power of a quantum information system increases exponentially with the number of qubits, rather than linearly.

Previous qubits have been made in GaAS but have had very short coherence times of a couple of nanoseconds. The Hitachi team has demonstrated an isolated double quantum-dot as a qubit built in silicon, but with a coherence time 100x longer than shown in other solid-state implementations.

To build a quantum computer it is necessary to produce enough qubits at so that they can interact within their coherence times and be manipulated to form architectures and then process data.

The Cambridge team has performed all the basic operations: initialisation, manipulation, and measurement, using electrical gates for initialisation and manipulation, and a single-electron transistor for measurement, Hitachi said.

The next project is to scale up from one device to a large quantum circuit.