C-NOT Breakthrough...

Technology Review

TECHNOLOGY REVIEW: In the race to build powerful quantum computers, many groups are competing to build logic gates that can process quantum information and still be connected together on a large scale.

One important question remains unanswered, however: what should the devices use to carry quantum information?

Schemes involving charged particles such as Ion traps, electron circuits and superconductors have long looked promising because the qubits they hold can be easily manipulated with electric and magnetic fields. Charged particles also interact easily with each other in a way that can be made to process data.

The problem, of course, is that stray fields also interact with charged particles, causing the quantum information they carry to leak away. Stray fields litter the universe like the plague and this severely reduces the utility of these types of devices.

One alternative is the humble photon, which is unaffected by stray fields and can travel many kilometres through a waveguide without interacting with the environment.

Primer: Controlled NOT gate (Wikipedia)
Physics arXiv: Controlled-NOT gate operating with single photons