A quantum view of the invisible universe

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Welcome

At the Royal Society’s Summer Science Exhibition 2024, we will be delivering an exhibit based around two research projects that Lancaster physicists are working on. These projects are using Quantum Technologies to build dark matter detectors, and at the exhibition we will have a number of hands-on exhibits to explore the fascinating physics of quantum technologies and the evidence for dark matter.

Selected for the Royal Society Summer Science Exhibition 2024

The QUEST-DMC experiment

QUEST is searching for dark matter by monitoring a box smaller than a matchbox filled with superfluid 3He. This detector is extremely sensitive because it is cooled down to a 100 millionths of a degree from absolute zero. This is by far the coldest liquid in the Universe. We use quantum technology for measuring changes in the energy contained by the superfluid target. Should dark matter be found, this experiment will transform our understanding of the Universe permanently.

An important part of this experiment is measuring the amount of radiation emitted from all of the materials that the experiment is made from. Radiation is naturally occurring and is found in very small quantities in almost every material. Radioactive decay from these materials can look very similar to a dark matter event, so minimising the background radiation is crucial to improving the sensitivity of the detector.

Bold QUEST DMC logo with two red lines above and below the text

The QSHS experiment

If dark matter is made from axions, then trillions of them should be streaming through our lab (and indeed through our bodies) every second. Apart from the fact that they interact extremely weakly with ordinary matter, we don’t know a lot about their properties. But if axions do exist, then there is one thing we can be sure of: when they pass through a magnetic field, a small fraction of them are converted into photons, i.e. particles of light[1]. This is the basis of our Quantum Search for the Hidden Sector[2] experiment (QSHS).

At the heart of the experiment is a light-tight metal cavity, which we place inside a strong electromagnet. If there are no axions, then the inside of the cavity should be completely dark. However, if axions do exist, then they will pass through the walls of cavity and occasionally convert into photons inside it. If we can detect these photons (and exclude other possibilities) then we will have discovered axionic dark matter.

Unfortunately, even with the strongest superconducting magnets, the signal that we expect is tiny. To make things trickier, we don’t know the frequency of the photons that should be created, although we do have good reason to believe they should correspond to radio frequencies[3]. In our experiment, we have designed the cavity to be rather like a tuneable antenna, so we can adjust its most sensitive frequency until we detect a signal. (At our exhibition, you will have the chance to do this.)

Why do we need quantum electronics? The signal power we expect is tiny – it’s about the same as your phone would pick up from a wireless router on Jupiter. This is so small that even miniscule quantum fluctuations of the electrical signal are enough to overwhelm the part we are looking for. We are developing amplifiers – using advanced superconducting technology, the same as is used in quantum computers – that will carefully isolate the axion signal despite this quantum noise. (At our exhibition, you will have the chance to use a model parametric amplifier, which is one of these technologies).

We don’t know whether axions exist, whether they’re what makes up dark matter, or whether the signal they generate will be at the frequency of our detector. But what we know is that this is a fantastic scientific challenge that will let us test quantum technology in one of the most demanding applications possible – and with the chance of making a revolutionary discovery about the nature of the universe.

[1] Light, like everything else in quantum mechanics, exists as both a particle and a wave. In everyday life it behaves like a wave, but here we are dealing with such small amounts of energy that its particle nature is important too.

[2] The “hidden sector” is jargon that particle physicists use to refer to hypothetical particles that interact only weakly and indirectly with the “visible sector” of particles that are known about. Our experiment is designed mainly to search for axions, but it can also be used to search for other hidden-sector particles.

[3] Radio waves are a form of light, exactly the same as visible light waves except that their frequency is lower. Like visible light, they exist in a range of frequencies, all of which must be searched for a possible axion signal.

  • Tineke Salmon and Dr Samuli Autti installing the QUEST-DMC detector on the Lancaster dilution refrigerator.

  • This 2cmx2cm "cell" is similar to the detector for the QUEST-DMC experiment and is cooled down to 100 millionth's of a degree above absolute zero.

  • Professor Yuri Pashkin and Dr Joshoua Esmenda with the superconducting cavity for the QSHS experiment.