A thermometer cooled to near absolute zero picks up the heat from a single particle. That's how cryogenic calorimeters work — instruments that catch ultra-rare events like neutrinoless double beta decay. But old thermistor thermometers respond slowly: in about a millisecond. For the next generation of experiments, that's not enough.
The solution is superconducting sensors that react in a hundred microseconds. The catch is that you need thousands of such sensors, each requiring its own wire. To avoid dragging hundreds of wires into the fridge, signals are multiplexed onto a single channel, like many voices over one cable. The new system does this at frequencies from 1 to 5 megahertz.
Now the detector is polled every 6 microseconds instead of every 10 milliseconds. This gives a clearer view of each signal's shape, helping to distinguish true events from random noise. The technology has already been tested on a real sensor and is ready for scaling up.
A temperature of 10 millikelvin is 30 times colder than outer space.