An electronic spin and a confined photon are complementary quantum mechanical objects which can be used to carry or manipulate quantum information. To combine them coherently would enable to manipulate and detect single spins but also to couple them over macroscopic distances thanks to the concepts of cavity quantum electrodynamics. This kind of architecture would allow one also to build quantum simulators for elementary magnetic systems.
Although progress has been made, in particular concerning the coupling of collective spin states or single charge states to cavity photons, no experiment had demonstrated so far the coherent coupling of a single spin to cavity photons. This problem arises from the fact that the natural coupling of a spin to the electromagnetic field is essentially magnetic, which makes it too weak in general to make it coherent.
The HQC team, in collaboration with the Theory team of the Laboratoire Pierre Aigrain could solve this problem by synthesizing an artificial spin orbit interaction in a single wall carbon nanotube connected to ferromagnetic electrodes [PRL manuscript]. Such a setup implements a single spin spin valve in a double quantum dot. The device is embedded in a high finesse microwave superconducting cavity. The HQC team could observe a very strong hybridization of the spin states in the nanotube and the photons trapped in the cavity, bringing the spin-photon system at the strong coupling threshold.
Besides its interest for quantum information, this works sheds new light on the artificial coupling between the spin and the orbital motion of the electron, which could be extended for synthesizing topological matter.
These results have been published in Science, on the 24th of July 2015.