Yesterday was again a mix of talks (including three from my group), chatting with friends and colleagues, looking around the vendor show (nice toys, and books, including the new edition of Purcell (and Morin) in SI units, and an intriguing graduate E&M text by Zangwill intended as a replacement for Jackson that focuses more on physics than on special functions), and answering email.
One session that was particularly fun was dedicated to artificial quantum matter. This topic is again worthy of a dedicated blog post that I will write sometime soon. The basic idea for the first few talks is a simple one: we know a number of different ways to impose spatially dependent potential energies on electrons constrained to move in 2d. (Note that while it is often convenient to act like the electrons in 2d electron gas or 2d surface states are free, as always this is shorthand for the true situation, where the single particle states are really Bloch-like states that exist due to the underlying periodic potential from the atoms). For example, if you impose a hexagonal lattice of potential wells on the free electrons, you get an effective band structure that looks like that of graphene. This has been done by etching on top of semiconductor structures, and by arranging molecules on the surface of Cu (as I'd mentioned here a year ago, work by Hari Manoharan). Making deeper potential wells gives you the chance to try to create an engineered system analogous to Mott insulators.
Another flavor of artificial quantum matter was discussed by Andrew Houck. If you make a little microwave resonator (a piece of stripline, superconducting to minimize loss), and then add in a superconducting quantum bit to act as a nonlinear element, you can have an effective photon-photon interaction in the cavity. Now consider wiring up a coupled network of such cavities, where the photons feel each other in each cavity and have some hopping from cavity to cavity. This raises the possibility of making "insulating" states of photons. As the speaker said, it's condensed matter without matter. Very thought provoking.