Designer quantum systems using cold atoms coupled to photonic crystals
Prof. Dr. Darrick Chang (ICFO - The Institute of Photonic Sciences, Castelldefels, Spain)

Significant efforts have been made to interface cold atoms with micro- and nano-photonic systems in recent years. Originally, it was envisioned that the migration to these systems from free-space atomic ensemble or macroscopic cavity QED experiments could dramatically improve figures of merit and facilitate scalability in applications such as quantum information processing. However, there is a growing body of work pointing to an even more intriguing possibility, that nanophotonic systems can yield fundamentally new paradigms to manipulate quantum light-matter interactions, which do not have an obvious counterpart in macroscopic setups.

Here, we describe an example of such a new possibility, involving the coupling of atoms to photonic crystals. In particular, we show that when atoms have transition frequencies aligned within photonic crystal bandgaps, the atoms can become dressed by localized photonic "clouds" of tunable size. This cloud behaves much like an external cavity, but one which follows the position of the atom. This phenomenon allows one to mediate and control long-range interactions between atomic internal degrees of freedom (spin), atomic motion (phonons), and photons. The multi-physics coupling can be utilized to design quantum systems with a rich variety of functionalities. We discuss several examples such as realizing bound photon "molecules," and pattern formation induced by spin entanglement.