Researchers create quantum light switch

In the experiments, Professor Arno Rauschenbeutel and his team captured light in 'bottle resonators'. If a bottle resonator was brought into the vicinity of a glass fibre carrying light, the two systems coupled and light crossed from the fibre into the resonator. "When the circumference of the resonator matches the wavelength of the light, we can make all the light from the fibre go into the bottle resonator and, from there, it can move into a second fibre", he explained. The system, consisting of the incoming and outgoing fibres and the resonator, is said to be extremely sensitive. "When we take a single rubidium atom and bring it into contact with the resonator, the behaviour of the system can change dramatically", said Prof Rauschenbeutel, who adds that, if the light is in resonance with the atom, it is possible to keep all the light in the original fibre, rather than transferring it to the bottle resonator and the outgoing glass fibre. The atom thus acts as a switch. The researchers now plan to explore the potential for this approach to be used in quantum communication systems, based on the rubidium atom being able to occupy different quantum states. "In quantum physics, objects can occupy different states at the same time", Prof Rauschenbeutel noted. "The atom can be prepared in such a way that it occupies both switch states at once. As a consequence, the states 'light' and 'no light' are simultaneously present in each fibre – effectively creating a quantum light switch. "It will be exciting to test whether such superpositions are possible with stronger light pulses," he concluded. "Somewhere, we are bound to encounter a crossover between quantum physics and classical physics."