Searching for dark matter

Eighty per cent of the mass of every galaxy, including our own, is dark matter. We know dark matter exists because we can observe its gravity, but its composition is among the greatest mysteries of modern physics. One promising suggestion is that dark matter is made of axions: hypothetical particles that were formed shortly after the Big Bang, have congregated in galaxies, and now pass through ordinary matter almost without trace.

We are part of the Quantum Sensing for the Hidden Sector collaboration, which is a consortium of eight UK universities supported by £4.8M SFTC grant, that aims to develop detectors to find – or rule out – axions in our galaxy. In a strong magnetic field, axions should decay with a small probability to ordinary photons, which we aim to detect using extremely sensitive electronic amplifiers.

For this experiment it is critical to develop electronics that reduces the noise to the minimum allowed by the laws of physics. Part of that noise comes from black-body radiation, which we must suppress by operating at very low temperature. Even more fundamental is the noise set by quantum uncertainty. However, quantum technology gives us a way to evade this, by using an effect known as squeezing. we are developing superconducting amplifiers that are optimised for performing squeezed measurements inside an axion detector.

Schematic of an axion detector. Inside a microwave cavity, passing axions interact with a magnetic field and are converted to photons. These photons are detected using a sensitive electronic amplifier. If axions exist, the signature will be a peak in the spectrum of the amplified signal, whose frequency corresponds to the axion mass.