New Scientist | Guide to the Quantum World | Silicon chips go quantum

New Scientist | Guide to the Quantum World | Silicon chips go quantum: "this is the first time that anyone has managed to entangle a pair of them. Entanglement is key to unlocking quantum computing power because qubits linked in this way share information, allowing lots of calculations to be carried out at once. The new chip is 'a pretty big step forward' says Martin Plenio, an expert in quantum computing at Imperial College, London.

In all computers, information is encoded as strings of 1s and 0s. In classical computers a bit stores either a 1 or a 0. Quantum computers are potentially far more powerful because a qubit can represent both at once. This means that an entangled pair of qubits can store four combinations (00, 01, 10 and 11) simultaneously. A two-qubit quantum computer will outperform a two-bit classical computer by carrying out four calculations at the same time.

Shen Tsai at the NEC Fundamental Research Laboratories in Ibaraki, Japan, and his colleagues have built a chip containing two squares of aluminium, called 'Cooper pair boxes', each about 0.1 micrometres across. Each box contains a few pairs of electrons, bound together in a state called a Cooper pair, and is connected to a reservoir of other electrons. When an electric field is applied across the box, an extra Cooper pair is pulled out of the reservoir and into the box. This changes the qubit 's state from 0 to 1. Removing a pair changes the state back. The quantum nature of the boxes allows them to exist in both states at once."