CNOT Gate...

Image Source: Joint Quantum Institute

Topics: Quantum Computer, Quantum Dots, Quantum Mechanics, Semiconductor Technology

The first quantum-logic device made from silicon has been unveiled by researchers in Australia and Japan. Their controlled-not (CNOT) gate, which is a fundamental component of a quantum computer, was made using conventional semiconductor manufacturing processes. The researchers now plan to scale up the technology to create a full-scale quantum-computer chip.

Spin doctors: Menno Veldhorst (left) and Andrew Dzurak with the equipment used to cool and monitor their CNOT gate.

Quantum computers exploit the weird laws of quantum mechanics to perform some calculations much faster than conventional computers – at least in principle. The main challenge facing physicists trying to build quantum computers is how to preserve fragile quantum bits (qubits) of information, which tend to deteriorate rapidly in real-world devices.

One approach is to use the spin of the electron – which can point up or down – as a qubit. Spin qubits have been made from tiny pieces of semiconductor called quantum dots, and quantum-logic devices have been made by coupling these qubits together. Unfortunately, the spin states in these devices rapidly deteriorate – or "decohere" – by interacting with nuclear spins in the compound-semiconductor materials normally used to make quantum dots.

Physics World: Silicon quantum logic gate is a first, Hamish Johnston