Light can be used to control individual atoms along nanofibres
The initial aim of the DIALON (From Dicke states to Anderson localisation of light in optical nanofibres) project was to investigate modification of the emission properties of the atoms in an optical waveguide induced by the linear and possibly regular arrangement of atoms along the nanofibre. Preliminary experimental work, however, revealed long-overlooked and significantly new effects: when light is tightly confined it becomes chiral, meaning that the propagation direction of the light field and the sign of the spin it carries are linked. Because these chiral properties were unexpected and opened a new field of study for this system, it was decided to reorient the DIALON project towards the new effect. The project was able to achieve sub-micrometre resolution manipulation of the trapped atoms. By exploiting the polarisation properties of fibre-guided light, it was shown that the atoms can be prepared in quantum spin states that depend on the position of the atoms around the nanofibre. Atoms located on opposite sides of the optical nanofibre, less than a micron away, can be addressed individually via microwave radiation. Beyond the great potential offered by tightly confined light, this work has provided powerful new tools for the control of both the quantum spin state and the position of trapped atoms. This will be important for the development of new nanophotonic integrated devices. The rest of the project was devoted to the development of such devices. The team used control over the quantum state of the trapped atoms and the polarisation of the nanofibre-guided light fields to realise an all-fibre-based optical memory: They were able to completely stop a probe light pulse, and to store it in the atomic ensemble, before recovering it. The nanofibre-trapped ensemble constituted an optical memory, one of the building blocks required for future optical quantum information networks. Efforts finally focused on the demonstration of an integrated non-reciprocal device, an optical isolator that acts as a one-way street for light. This should open a path to the development of novel integrated optical devices for fibre-based classical and quantum networks.
Keywords
Nanofibres, DIALON, optical waveguide, trapped atoms, quantum spin state