Researchers at Delft University of Technology have created a detector that enables the detection of a single photon’s worth of radio frequency energy. The chip is only 10 mm square and the team plans to use it to explore the relationship of mass and gravity to quantum theory.
The chip has immediate applications in MRI and radio astronomy. Traditionally, detecting a single photon at radio frequencies is difficult due to the significance of thermal fluctuations. At lower frequencies, cryogenic cooling can reduce the issue, but as frequency increases the fluctuations are harder to tame.
The trick requires a qubit that samples the radio frequency energy. While the radio source is at 173 MHz, the qubit is at 1 GHz, allowing a fine time resolution. Coupling of the two is via an LC circuit that uses a Josephson junction which, of course, requires very cold temperatures.
The paper is pretty math-heavy and we haven’t seen a lot of activity around homemade Josephson junctions. However, if you have access to niobium and liquid helium, this lab experiment looks like you could try it. Or watch [Sumner Davis] do roughly the same thing during a lecture at Berkeley. Keep in mind that dealing with liquid helium is much more difficult than liquid nitrogen.
It won’t help you with junctions, but you can make some relatively high-temperature superconductor material yourself. It turns out that the super cold junctions have a lot of applications in creating very precise voltage references.