Quantum Entanglement, Dark Counts, Coincidence Detection

[caraher]

60. Since you're an electronics person...

the folks at Whitman also used homemade coincidence detectors. Because I'm a bit shakier on all that I was happy to sponge off their efforts and do nothing little more than build the little box that makes sure the signals are properly terminated and routed to the correct ribbon cable wires It also helps that I have a LabVIEW license; if I didn't I'd have had to work out how to communicate with their FPGA via RS-232, which isn't hard but which is another task.

The "traditional" approach to all this (for people who have all kinds of nuclear instrumentation lying about) is to use one detector to provide a "start" pulse to a time-to-amplitude converter (TAC) and use the second detector and a fixed delay to provide a stop pulse. They get a histogram of arrival times which helps them set a window they define as good for coincidence counting, then generally use a single-channel analyzer... I went through this once, but I can't say it really mattered for what I'm doing. As long as you don't do something silly like have one optical or signal path vastly longer than the other relative to the coincidence window width (remember that 1 foot = 1 nanosecond!), simple coincidence circuits should work just fine.