Nature Photon. 9, 320–325 (2015); Nature Photon. 9, 326–331 (2015)

Quantum simulators are cool because they provide a playground to study many-body physics. For example, you can build your own (simplified) analogue of a solid-state system by trapping ultracold atoms in an optical lattice. You can configure the lattice geometry and tune the short-range interactions between the atoms — providing all the ingredients necessary to emulate all sorts of models interesting to condensed-matter physicists. Still, one knob has been missing: controllable long-range interactions. Two studies have now shown how to produce and tune variable-range interactions between atoms, with the help of photonic crystals.

Inspired by the idea of optical cavity-mediated interactions, the two studies made use of photons confined in photonic structures. James Douglas and co-workers looked at one-dimensional photonic waveguides, whereas Alejandro González-Tudela and colleagues opted for a two-dimensional geometry. The beauty of these approaches is that the features of the photonic crystals' optical modes render the interactions both strong and controllable. And the ability to tune the interaction range from short to long holds exciting possibilities for the quantum simulation of many-body systems.