Searching for dark matter with the world’s coolest quantum detectors

One of science’s greatest mysteries could be one step closer to being solved. About 80% of the matter in the universe is dark, meaning it cannot be seen. In reality, dark matter is constantly passing through us—perhaps at the rate of trillions of particles per second.

We know it exists because we can see the effects of its gravity, but so far experiments have failed to detect it.

Using the most advanced quantum technologies, scientists from Lancaster University, University of Oxford and Royal Holloway, University of London are building the most sensitive dark matter detectors to date.

Their public exhibition entitled “A quantum view of the invisible universe” is on display at this year’s flagship Royal Society Summer Science Exhibition from 2-7 July 2024. Related research is also published in Journal of Low Temperature Physics.

Researchers include Dr. Michael Thompson, Professor Edward Laird, Dr. Dmitry Zmeev and Dr. Samuli Autti from Lancaster, Professor Jocelyn Monroe from Oxford and Professor Andrew Casey from RHUL.

EPSRC member Dr. Autti said: “We are using quantum technology at ultra-low temperatures to produce the most sensitive detectors yet. The aim is to observe this mysterious matter directly in the laboratory and solve one of the biggest mysteries in science.”

There is indirect observational evidence for the typical density of dark matter in a galaxy, but the mass of individual particles and their possible interactions with ordinary atoms are unknown.

The theory of particle physics suggests two likely candidates for dark matter: new particles with interactions so weak that we have not yet observed them, and very light wave-like particles called axions. The team is building two experiments, each will search for one.

Of these two candidates, new particles with ultraweak interactions could be detected through their collisions with ordinary matter. However, whether these collisions can be identified in an experiment depends on the mass of the dark matter being sought. Most searches to date would have been able to detect dark matter particles between 5 and 1,000 times the mass of a hydrogen atom, but it is possible that much lighter dark matter candidates have been missed.

The Quantum Enhanced Superfluid Technologies for Dark Matter and Cosmology (QUEST-DMC) team aims to achieve world-leading sensitivity to collisions with dark matter candidates ranging in mass from 0.01 to a few hydrogen atoms. To achieve this, the detector is made of superfluid helium-3, cooled to a macroscopic quantum state, and equipped with superconducting quantum amplifiers. The combination of these two quantum technologies creates a sensitivity for measuring the extremely faint signatures of dark matter collisions.

In contrast, if dark matter is made up of axions, they will be extremely light – more than a billion times lighter than a hydrogen atom – but correspondingly more abundant. Scientists wouldn’t be able to detect collisions with axions, but instead can look for a different signature—an electrical signal produced when axions decay in a magnetic field.

This effect can only be measured with an extremely sensitive amplifier that operates with the highest precision quantum mechanics allows. The Quantum Sensors for the Hidden Sector (QSHS) team is therefore developing a new class of quantum amplifier that is perfectly suited for searching for the axion signal.

A booth at this year’s show will allow visitors to observe the unseen with imaginative hands-on exhibits for all ages.

To demonstrate how we infer dark matter from galaxy observations, there will be a gyroscope in a box that moves in surprising ways thanks to an invisible angular momentum. There will also be glass balls that are transparent in liquid, showing how invisible matter can be observed through clever experimentation.

A lighted dilution refrigerator will show how the team achieves ultra-low temperatures, and a model dark matter particle collision detector will show how our universe would behave if dark matter behaved like normal matter.

Visitors can then search for dark matter with a model axion detector by scanning the frequency of a radio receiver, and can also create their own parametric amplifier using a pendulum.

Cosmologist Carlos Frenk, Fellow of the Royal Society and Chair of the Public Engagement Committee, said: “Science is vital because it helps us understand the world we live in – past, present and future. I encourage visitors of all ages to come with an open mind, curiosity and enthusiasm and celebrate incredible scientific achievements that benefit us all.”