The hunt for dark matter is about to get a lot cooler. Scientists are developing ultra-cold quantum technology to search for the most elusive and mysterious things in the universe, which currently represent one of science’s greatest mysteries.
Despite the fact that dark matter exceeds the amount of ordinary matter in our universe by about six times, scientists do not know what it is. This is at least in part because no human-designed experiment has been able to detect it.
To tackle this conundrum, scientists from several UK universities teamed up to create two of the most sensitive dark matter detectors ever presented. Each experiment will search for a different hypothetical particle that might contain dark matter. Although they share some of the same qualities, the particles also have some radically different characteristics, requiring different detection techniques.
The equipment used in both experiments is so sensitive that the components must be cooled to a thousandth of a degree above absolute zero, the theoretical and unattainable temperature at which all movement of atoms will stop. This cooling must occur to prevent interference or “noise” from the world from corrupting the measurements.
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“We are using quantum technology at ultra-low temperatures to build the most sensitive detectors to date,” team member Samuli Outti of Lancaster University said in a statement. “The goal is to observe this mysterious matter directly in the laboratory and solve one of the greatest enigmas in science.
How dark matter has left scientists in the cold
Dark matter poses a serious problem for scientists because, although it makes up about 80% to 85% of the universe, it remains effectively invisible to us. This is because dark matter does not interact with light or “everyday” matter – and if it does, these interactions are rare or very weak. Or maybe both. We just don’t know.
However, because of these characteristics, scientists know that dark matter cannot be composed of electrons, protons, and neutrons—all part of the family of baryon particles that make up everyday matter in things like stars, planets, moons, our bodies, ice cream, and the neighbor’s cat. All the “normal” things we can see.
The only reason we think dark matter exists at all is actually that this mysterious substance has mass. This is how it interacts with gravity. Dark matter can affect the dynamics of ordinary matter and light through this interaction, which suggests its presence.
Astronomer Vera Rubin discovered the existence of dark matter, previously theorized by scientist Fritz Zwicky, because she saw some galaxies spinning so fast that if their only gravitational influence came from visible, baryonic matter, they would collapse. What scientists really want, however, is not a conclusion, but rather a positive detection of dark matter particles.
One of the hypothetical particles currently considered prime suspects for dark matter is the very light “axion”. Scientists also theorize that dark matter may be made up of more massive (as yet unknown) new particles with such weak interactions that we haven’t yet observed them.
Both axions and these unknown particles would exhibit ultraweak interactions with matter that could theoretically be detected with sufficiently sensitive equipment. But two prime suspects mean two investigations and two experiments. This is necessary because current searches for dark matter typically focus on particle masses between 5 times and 1000 times the mass of a hydrogen atom. This means that if dark matter particles are lighter, they may be missed.
The Quantum Enhanced Superfluid Technologies for Dark Matter and Cosmology (QUEST-DMC) experiment was designed to detect ordinary matter colliding with dark matter particles in the form of weakly interacting unknown new particles that have masses between 1% and several times more greater than that of a hydrogen atom. QUEST-DMC uses superfluid helium-3, a light and stable isotope of helium with a nucleus of two protons and one neutron, cooled to a macroscopic quantum state to achieve record sensitivity in detecting ultraweak interactions.
However, QUEST-DMC would not be able to detect extremely light axions, which are assumed to have masses billions of times lighter than a hydrogen atom. This also means that such axions could not be detected by their interaction with ordinary particles of matter.
Yet what they lack in mass, axions are supposed to make up for in numbers, assuming these hypothetical particles are extremely abundant. That means it’s better to look for these dark matter suspects using a different signature: the tiny electrical signal resulting from axions decaying in a magnetic field.
If such a signal exists, detecting it will require stretching detectors to the maximum level of sensitivity allowed by the rules of quantum physics. The team hopes that their quantum sensors for the hidden sector (QSHS) quantum amplifier could do just that.
If you’re in the UK, the public can see both the QSHS and QUEST-DMC experiments at Lancaster University’s Summer Science Exhibition. Visitors will also be able to see how scientists infer the presence of dark matter in galaxies using a gyroscope in a box, which moves strangely due to an invisible angular momentum.
The exhibit also includes a light-dilution refrigerator to demonstrate the ultra-low temperatures required by quantum technology, while its model of a dark matter particle collider detector shows how our universe would behave if dark matter interacted with matter and light precisely as everyday matter does.
The team’s reports describing the QSHS and QUEST-DMC experiments were published in The European Physical Journal C and on the paper repository site arXiv.
