Can dark matter change the structure of atoms by interacting with photons? Optically based atomic clocks: The Physikalisch-Technische Bundesanstalt (PTB) used the Collaborative Research Center DQ-mat and the Cluster of Excellence QuantumFrontiers to compare two different kinds of these clocks. It is the most precise attempt to date to find an interaction between photons and ultralight dark matter.
This work has raised the detection limits for a possible coupling by more than an order of magnitude across a broad range of dark matter particle masses. Although there is no evidence of a dark matter coupling, the research contributes to a better understanding of dark matter’s nature and potential interactions. The investigation’s findings can be found in the most recent issue of the journal Physical Review Letters.
Astronomical observations suggest that there is so-called “dark matter,” which only interacts with ordinary visible matter through gravity and accounts for more than 80% of all matter. The term “dark” refers to this kind of matter because there is currently no evidence to support any kind of interaction with photons—the fundamental particles of which light is also made—which is why it is referred to as such. What dark matter is made of and whether or not it interacts with ordinary matter is still a great mystery.
A particularly promising theoretical approach suggests that extremely light particles that behave more like waves than individual particles could make up dark matter. referred to as “ultralight” dark matter The fine-structure constant’s tiny oscillations would result from weak interactions between dark matter and photons in this scenario, which was previously unknown.
The natural constant that shows how strong the electromagnetic interaction is is called the fine-structure constant. It has an impact on the transition frequencies that are used as references in atomic clocks because it determines the atomic energy scales. Comparing atomic clocks can be used to look for ultralight dark matter because different transitions are sensitive to changes in the constant to varying degrees. An atomic clock that is particularly sensitive to possible changes in the fine-structure constant has been utilized by PTB researchers for this purpose.
In order to accomplish this, months-long measurements were used to compare this sensitive atomic clock to two others with lower sensitivities. Oscillations, which are characteristic of ultralight dark matter, were looked for in the measurement results. Even when examined more closely, the dark matter remained “dark” because there were no significant oscillations observed. As a result, the mysterious dark matter could not be found. New experimental upper limits on the strength of a possible coupling of ultralight matter to photons were established because there was no signal. Over a wide range, the previous limits were improved by more than an order of magnitude.
The researchers also looked into the possibility that the fine-structure constant might change over time, such as by slowly increasing or decreasing. The data did not reveal such a variation. In this case, the limits that were already in place were also tightened, indicating that the constant stays the same even over long periods of time.
In this work, two of the three atomic clocks were realized in a single experimental setup, in contrast to previous clock comparisons, where each atomic clock required its own experimental system. For this reason, two different progress frequencies of a solitary caught particle were utilized. On both optical transitions, the ion was probed in turn. This is an important step toward making optical frequency comparisons even smaller and more reliable, which could be useful for searching for dark matter in space in the future, for instance.
More information: M. Filzinger et al, Improved limits on the coupling of ultralight bosonic dark matter to photons from optical atomic clock comparisons, Physical Review Letters (2023). DOI: 10.1103/PhysRevLett.130.253001. On arXiv: DOI: 10.48550/arxiv.2301.03433
