As a quantum information theorist, the cleanest types of results I can get are proofs that something is possible, impossible or optimal. Much of my work focused on these types of results in the context of measurements and non-locality. As a physicist, it is always nice to bring these conceptual ideas closer to the lab, so I try to collaborate with experimentalists. The types of problems an experimental group can work on are constrained by technical capabilities. In the case of Amr Helmy’s group, they specialize in integrated photonic sources so I now know something about integrated optics.
When I started learning about the possibilities and constraints in the group, I realized that the types of devices they can fabricate are much better suited for work in continuous variables as opposed to single photons. I also realized that no one explored the limitations of these types of devices. In other words, we did not know the subset of states that we could generate in principle (in an ideal device).
In trying to answer this question we figured out that, with our capabilities, it is in principle (i.e in the absence of loss) possible to fabricate a device that can generate any Gaussian state (up to some limitations on squeezing and displacement). What turns out to be even nicer is that we could have a single device that can be programmed to generate any N-mode Gausssian state. The basic design for this device was recently posted on arXiv.
We left the results fairly generic so that they could be applied to a variety of integrated devices, using various semiconductors. The next step would be to apply them to something more specific and start accounting for loss and other imperfections. Once we figure that out, we (i.e. the fab guys) an go on to building an actual device that could be tested in the lab.