It has been an insanely busy 2014 for me. I spent nearly the entire month of March elsewhere, with the APS March Meeting in Denver and then the workshop Information and Interaction that I organized with Dean Rickles which turned out to be a resounding hit (videos will be posted soon — I need to get through the end of the semester first). At any rate, I did find a bit of time to delve into my Mach-Zehnder interferometer in recent weeks and am pleased to report that I have figured out one of the problems I was having. Sometimes it is helpful just to have someone around to bounce ideas off of, and my former student, Eric Holland, who works in superconducting qubits and returned to campus to give a talk, kindly obliged. Of the many problems I was having last year when trying to understand the basic interference pattern, one of the more perplexing was the fact that I seemed to only get an interference pattern for specific sizes of the central square of the interferometer. I am happy to report that this was just a relic of the fact that at certain sizes, the interferometer is more difficult to align. I was able to get a pattern for every size I tried when Eric was here (maybe MZIs only work when someone named Eric Holland is in the room?).
I discussed my general issues with Markus Aspelmeyer over dinner in Denver and he maintained that the classical pattern is a result of the fact that the beam widens as it propagates. Last year, I did the ray tracing for such a spreading beam and, faithfully keeping track of the phases and wavelengths, still couldn’t get the result I expected. I’m going to go back and retry it because Markus seemed fairly confident that this was the explanation. He pointed out that the coherence lengths for the lasers I work with should be very, very long and thus should not be an issue. At any rate, in order to do what I need to do eventually, this all means I will have to figure out how to collimate the beam.
Anyway, Eric and I did figure out that there are vibrational issues affecting the stability of the pattern which means next fall I’m going to have to get some students to develop a damping system for it. But progress has been made! Not bad for a theorist, eh?