A multi-institutional collaboration of engineers has developed an experimental approach for the detection of dark matter. While scientists are sure that dark matter — which accounts for 85% of the matter in the universe — exists by its gravitational effects, they have yet to find any direct evidence of the substance. “It could be made up of black holes, or it could be made up of something trillions of times smaller than an electron, known as ultralight dark matter,” said Swati Singh, an assistant professor of electrical and computer engineering at the University of Delaware. Singh is among a small group within the dark matter community that wondered if scientists were looking for the right kind of dark matter. Specifically, Singh aimed to resolve the question of whether dark matter is much lighter than what traditional particle physics experiments look for. Another possibility is that dark matter is made up of dark photons, a type of dark matter that would exert a weak oscillating force on normal matter, causing a particle to move back and forth. This potentiality would be difficult to measure, due to dark matter’s ubiquity. With that theory in mind, Singh, doctoral student Jack Manley, and collaborators at the University of Arizona and Haverford College proposed a new way to look for dark matter particles by repurposing existing tabletop sensor technology. Jack Manley (left) is a University of Delaware doctoral student and Swati Singh is an assistant professor in the College of Engineering’s Department of Electrical and Computer Engineering. Courtesy of Evan Krape and Jeffrey C. Chase. The collaborators believe they can use optomechanical accelerometers that detect changes in velocity as sensors to detect and amplify that oscillation. “If the force is material dependent, by using two objects composed of different materials, the amount that they are forced will be different, meaning that you would be able to measure that difference in acceleration between the two materials,” said Manley, lead author of the paper. Dalziel Wilson, assistant professor of optical sciences at the University of Arizona, compared an optomechanical accelerometer to a tuning fork. “It’s a vibrating device that, due to its small size, is very sensitive to perturbations from the environment,” he said. The researchers proposed an experiment to detect the presence of these theorized dark photons. The experiment used a membrane made up of silicon nitride and a fixed beryllium mirror to bounce light between the two surfaces. If the distance between the two materials changed, the researchers would know from the reflected light that dark photons were present because the silicon nitride and beryllium possess different material properties. That collaboration was essential in devising this experiment, Manley said; he and Singh provided the theoretical basis and worked with Wilson and Arizona doctoral student Dey Chowdhury on the calculations that went into the blueprint for building their proposed tabletop accelerometer sensor. Daniel Grin, a cosmologist and assistant professor of physics at Haverford College, provided insight on the particle physics aspects of ultralight dark matter, such as why it would be ultralight, why it might couple to materials differently, and how it might be produced. The new work builds on a previous study showing that certain types of ultralight dark matter would connect, or couple, with normal matter in a way that would cause a periodic change in the size of atoms. While small fluctuations in the size of a single atom may be difficult to notice, the effect is amplified in an object composed of many atoms, and further amplification can be achieved if that object is an acoustic resonator. The initial round of collaboration evaluated the performance of several resonators made of diverse materials ranging from superfluid helium to single-crystalline sapphire, and found these sensors can be used to detect that dark matter-induced strain signal. The research was supported in part by funding from the National Science Foundation. The current research was published in Physical Review Letters (www.doi.org/10.1103/physrevlett.126.061301).