Researchers at ATAP have proposed an innovative technique that uses quantum sensing to detect dark matter particles in lower mass ranges than is possible with existing technologies.
By Carl A. Williams, February 22, 2024
Dark matter appears to make up over a quarter of all the matter and energy in our universe and is about five times more abundant than ordinary matter. However, dark matter is invisible, emitting no light or energy, and so cannot be detected using conventional sensors and detectors.
Now, researchers from the Accelerator Technology & Applied Physics (ATAP) Division at Berkeley Lab, in collaboration with colleagues from Princeton University and the California Institute of Technology, have proposed a novel approach that uses quantum sensing of the spin of helium-3 (3He) atoms—a stable (and the least abundant) isotope of helium—evaporated from the surface of a film of liquid helium to detect dark matter particles. The work promises a new technique that could extend the search for dark matter into mass ranges below the detection threshold of current detectors and could lead to more powerful sensors and detectors for applications in particle physics, astrophysics, and cosmology.
“When we look at the mass balance of the universe, only a small percentage, around 5%, is made up of matter we can see,” explains Thomas Schenkel, a senior scientist and head of ATAP’s Fusion Science & Ion Beam Technology Program, who initiated the collaboration.
“The vast majority of matter is dark matter, named because we don’t know what properties to assign to it. However, we know dark matter exists because it interacts with normal matter through gravity.”
Because dark matter constitutes the vast majority of the universe’s mass, it has guided the evolution and structure of the universe and the formation of visible, everyday matter. Therefore, searching for dark matter is “essential to understanding the universe’s size, shape, and future,” says Schenkel.
The search for dark matter
The search for dark matter has been highlighted as a top priority in the recently released 2023 P5 Report: A Roadmap for Particle Physics. The report, which outlines particle physicists’ recommendations for the next decade, states that: “Answering some of the deepest questions about particle physics itself requires … revealing the underlying nature of dark matter …” and that: “Developments in detector instrumentation lay the foundation for future campaigns to identify dark matter in new scenarios.”
While the search for dark matter has been a multi-decadal effort by scientists from around the world, the direct detection of dark matter has primarily focused on detecting so-called weakly interacting massive particles, or WIMPs, via nuclear recoils in which dark matter with mass in the GeV range transfers energy by elastic scattering.
However, as the mass of dark matter candidates drops below around 1 GeV (about the mass of a proton), the resulting scattering events can fall below the detection threshold or get buried in noise in the detectors.
“Searches for WIMPs have achieved amazing sensitivity but, to date, have not confirmed the existence of high-mass dark matter particles,” says Schenkel. “Consequently, scientists are focusing on searching for dark matter in energy ranges well below 1 GeV, and it has become a hot topic for seeking novel approaches that probe for dark matter candidates as light as a few keV.”
In recent years, progress in dark matter theory has spurred advances in direct-detection technologies with quantum sensing. This emerging sensor technology detects events by tracking quantum properties, such as spin coherence in a detector or sensor.
In light of these advances, the researchers proposed a detector system based on quantum sensing that uses low-energy phonons—quanta of vibrational energy that are analogous to photons of light—created through rare interactions of dark matter with an absorber; for example, a polar crystal like sodium iodide.
“This absorber is coated with a thin helium film, and dark matter interactions lead to the quantum evaporation of 3He atoms,” explains Schenkel. “These 3He atoms are then collected on an adjacent surface and transported to a readout system with a type of charged coupling device that is patterned onto the collector surface.”
The readout system, he says, is the heart of the quantum sensor and operates by tracking spin decoherence of electron spins induced by the nuclear spins of 3He atoms. He notes that detecting single nuclear spins has been demonstrated in several ways, including using electrons in quantum dots or color centers.
Therefore, the basic principle behind the detector, says Schenkel, is to use quantum coherence to track the rare and small energy transfer events when dark matter particles in the lower-mass regime interact with liquid helium films more sensitively.
He adds that the proposed dark matter detector combines elements from previous work on spin coherence with results from studies of electrons on liquid helium, pioneered by Stephen Lyon from Princeton, and theoretical studies by Kathryn Zurek of the California Institute of Technology, for a system that addresses the problem of detecting these very rare, tiny energy transfer events.
“The technique would allow us to search regions of the dark matter mass maps not yet explored,” says Schenkel. “It could also be tuned for different binding energies of the 3He atoms, allowing us to change the threshold for the region of dark matter to be explored.”
To learn more …
- A. Lyon, Kyle Castoria, Ethan Kleinbaum, Zhihao Qin, Arun Persaud, Thomas Schenkel, and Kathryn M. Zurek. “Single phonon detection for dark matter via quantum evaporation and sensing of 3He,” Phys. Rev. D109, 023010, 2024, https://doi.org/10.1103/PhysRevD.109.023010
- Newly Released Roadmap for Particle Physics Includes Support for Berkeley Lab Projects
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