Diagram showing two separately addressable sites, which could be used to implement a photonic phase gate. The set-up could also be used to study photon hopping over macroscopic length scales, because of the strong dipole-dipole interactions between highly excited Rydberg states. (Courtesy: Charles Adams)

Stored photons interact in atom cloud

Feb 5, 2013

Physicists in the UK have come up with a new way of storing a handful of photons in an ultracold atomic gas, in which strong interactions between neighbouring photons can be switched on and off using microwaves. The team believes that the technique could be used to create optical logic gates in which single photons could be processed one at a time. The method could also prove useful for connecting quantum-computing devices based on different technologies.

Optical photons make very good “flying” quantum bits (qubits) because they can travel hundreds of kilometres through fibres without losing their quantum information. However, it is very difficult to get such photons to interact either with each other or with “stationary” qubits such as those based on trapped ions or tiny pieces of superconductor. Exchanging quantum information between such devices can therefore be tricky.

What Charles Adams and colleagues at Durham University have now done is come up with a way of storing individual optical photons in highly excited states of an atomic gas. Once stored, the photons can be made to interact strongly, before being released again. An important feature of the technique is that it uses microwaves, which are also used to control some types of stationary qubit.

Read more: Stored photons interact in atom cloud – physicsworld.com.

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