Searching for dark matter with the coldest quantum detectors in the world

One of science’s greatest mysteries may be one step closer to being solved. About 80% of the matter in the universe is dark, meaning it can’t be seen. In fact, dark matter is constantly passing through us, possibly at trillions of particles per second.

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

Scientists from Lancaster University, the University of Oxford and Royal Holloway, University of London, are using the most advanced quantum technologies to build the most sensitive dark matter detectors yet.

Their public exhibition entitled “A Quantum View of the Invisible Universe” will be showcased at this year’s Royal Society’s flagship Summer Science Exhibition from 2 to 7 July 2024. Related research has also been published in the Journal of Low Temperature Physics.

The 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 Fellow Dr Autti said: “We are using ultra-low temperature quantum technologies to build the most sensitive detectors yet. The aim is to observe this mysterious matter directly in the laboratory and solve one of the greatest mysteries in science.”

There is indirect observational evidence that there is a typical density of dark matter in the galaxy, but the masses of the particles that make them up and their possible interactions with ordinary atoms are unknown.

Particle physics theory suggests two likely candidates for dark matter: new particles with interactions so weak that we haven’t yet observed them, and very light wave-like particles called axions. The team is building two experiments, one to look for each.

Of the two candidates, new particles with ultraweak interactions could be detected by their collisions with ordinary matter. However, whether these collisions can be identified in an experiment depends on the mass of the dark matter being searched for. Most searches to date have been able to detect dark matter particles between five and a thousand times heavier than 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 industry-leading sensitivity for collisions involving dark matter candidates with masses between 0.01 and 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. Combining these two quantum technologies provides the sensitivity to measure extremely faint signatures of dark matter collisions.

In contrast, if dark matter is made 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 they could instead look for a different signature—an electrical signal created when axions decay in a magnetic field.

This effect can only be measured with an extremely sensitive amplifier operating at the highest precision allowed by quantum mechanics. The Quantum Sensors for the Hidden Sector (QSHS) team is therefore developing a new class of quantum amplifiers that are perfectly suited to search for an axion signal.

This year’s stand offers visitors the opportunity to observe the invisible with imaginative, interactive exhibits for all ages.

To show how we infer dark matter from observing galaxies, there will be a gyroscope-in-a-box that moves in surprising ways due to invisible angular momentum. There will also be glass marbles that are transparent in liquid, showing how invisible masses can be observed using clever experiments.

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

Visitors can then use a model axion detector to search for dark matter by scanning the frequency of a radio receiver, or 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 to helping us understand the world we live in – past, present and future. I urge visitors of all ages to come with an open mind, curiosity and enthusiasm, and celebrate incredible scientific achievements that benefit us all.”