Prof. Szymon Pustelny, together with an international team of scientists from the Chinese university USTC, has published an article entitled “Constraints on axion dark matter by distributed intercity quantum sensors” in the prestigious journal Nature, devoted to the latest research on dark matter. The scientists achieved something previously thought unattainable – under laboratory conditions, they reached a level of measurement precision surpassing that derived from observations of the cosmos.

Dark matter – one of the greatest mysteries of the Universe

Dark matter is one of the greatest mysteries of modern cosmology. Although it remains invisible to telescopes, its gravitational influence on the Universe is crucial. For example, if it did not exist, galaxies, stars, and planets would never have formed, and life on Earth could not have emerged.

Our knowledge of dark matter is still very limited – it is not known, for instance, what it is made of. For this reason, scientists have been formulating various hypotheses for many years. One of the most frequently considered assumes that dark matter consists of axions – hypothetical particles millions of times lighter than the lightest particles currently known, namely neutrinos.

How was dark matter studied? Experimental research by Prof. Pustelny’s team

Prof. Szymon Pustelny, together with collaborators from the Chinese university USTC, tested the so-called “exotic” hypothesis of the existence of dark matter. It assumes that dark matter is not distributed uniformly throughout the cosmos, but instead forms gigantic structures known as topological defects.

These can be imagined as invisible “bubbles,” through whose walls (so-called domain walls) the Earth passes during its journey through the Milky Way. If such a wall actually exists, its passage through our planet should produce a subtle effect that could be registered by ground-based sensors.

For this purpose, the scientists built a network of extraordinary quantum sensors operating like ultra-precise compasses. If the Earth were to pass through the wall of such a “bubble,” the “needles” of these compasses would simultaneously “twitch” in many devices. The experiment was conducted in China, in laboratories located more than 300 km apart. Such a distance significantly limited the possibility of an accidental coincidence of signals.

What was the result of the experiment?

During several months of measurements, the sensors did not register the sought-after signal. It might therefore seem that the experiment ended in failure. In reality, however, this result constitutes an important success, as it made it possible to verify and falsify one of the significant theoretical models.

Until now, parameters describing such interactions had been determined on the basis of cosmic observations, including the famous explosion of Supernova 1987A. It was also assumed that if axions exist, their influence on matter must be weaker than what would follow from the rate of stellar cooling.

The team involving Prof. Pustelny demonstrated that, under laboratory conditions on Earth, it is possible to carry out measurements up to 40 times more precise than those based on astronomical observations. The use of innovative noise-filtering techniques – similar to those employed in the detection of gravitational waves in LIGO experiments – as well as new quantum sensors, made it possible to investigate model parameters that had previously remained beyond the scope of analysis.

What’s next in the search for dark matter?

The results published in Nature provide an important guideline for the scientific community, indicating which areas should no longer be pursued in the search for dark matter, while at the same time opening up new directions for further research.

Scientists are planning to build even more sensitive sensor networks that could detect signals originating from the most violent cosmic phenomena, such as black hole mergers.

Prof. Szymon Pustelny will continue his research on dark matter also within the framework of a Polish–American project funded by the Fulbright STEM Impact Award program.