Obstacle for quantum computer

Thursday July 14, 2005

Guardian

Many scientists dream of building a quantum computer, but now Dutch physicists have shown that this dream is going to hit a fundamental boundary, potentially putting the brakes on quantum computing.

Jeroen van den Brink, of Leiden University in the Netherlands, and his colleagues have carried out theoretical calculations to investigate how long qubits (quantum bits used to store information) can hold information for.

In the journal Physical Review Letters, they reveal that a qubit's ability to hold information decays over time, losing the information as it does so. What is more, the smaller the qubit, the faster the information decays. "To build a quantum computer we need to be able to store information for longer than the time it takes to do the computation," says Van den Brink.

Currently the most promising qubits are likely to be able to store information for around one second, but that is unlikely to be long enough. Larger qubits will be able to hold information for longer, but will defeat the object of a quantum computer being small and fast.

The scientist's predictions still need to be verified by experiment, but if they are correct they will present a huge hurdle to quantum computing.

Guardian Unlimited Guardian Newspapers Limited 2005