Arrays of Cold Atoms Coupled to Nanoscale Waveguides: Towards Quantum Non-Linear Optics

Deterministic interactions between single photons, i.e. quantum non-linear optics, is a long-standing goal in optical physics, with applications to quantum optics and quantum information science. However, single photons usually do not interact with each other and the interaction needs to be mediated by an atomic system. Enhancing this coupling has been the driving force for a large community over the past two decades. One pioneering approach is known as cavity quantum electrodynamics (CQED), where a single atom and a single photon can be strongly coupled via a high-finesse cavity. Cavity-QED led to a better understanding of fundamental aspects of light-matter interaction and to various seminal demonstrations.

Strong transverse confinement in single-pass nanoscale waveguide recently triggered various investigations for coupling guided light and cold atoms, without a cavity. Specifically, a subwavelength waveguide can provide a large evanescent field that can interact with atoms trapped in the vicinity. An atom close to the surface can absorb a fraction of the guided light as the effective mode area is comparable with the atom cross-section due to the tight transverse confinement.

The LKB team recently developed an experiment in this direction. Using a nanofiber with a 400-nm diameter and a few thousands atoms trapped around, the team recently realized a first all-fibered quantum memory for light. The team also demonstrated the very efficient reflection of single photons by an ordered one-dimensional array of trapped atoms.

The goal is now to push further the accessible non-linearity and to demonstrate in such waveguided-configuration quasi-deterministic single-photon emission and single-photon controlled optical switches and transistors, with applications to quantum state engineering and quantum networks.

References:
Demonstration of an optical memory for tightly guided light in an optical nanofiber, PRL 114, 180503 (2015).
Large Bragg reflection from one-dimensional arrays of trapped atoms near a nanoscale waveguide, PRL 117, 133603 (2016).
See also: “Making a mirror from a line of atoms” in Optics and Photonics News.

Contact: Prof. Julien Laurat, julien.laurat at upmc.fr