As physics and engineering extend their reach to the control of single excitations of nature, we gain the ability to explore and even design the interaction of matter and energy in fundamentally new ways. One of the most interesting opportunities this presents is controllable interactions between many quantum particles — such as electrons — which is traditionally the realm of condensed matter physics. The questions we asked ourselves were these: Can we also do this with light? Can it be useful? We show that the answer is YES!