September 11, 2025
Paul Dailing
“Quantum sound” will aid the searches for both nuclear weapons and dark matter
| UChicago Pritzker School of Molecular Engineering Prof. Andrew Cleland (left) and Prof. Paolo Privitera of the Astronomy and Astrophysics Department and Physics Department (right) are heading a team that recently received a $5 million Defense Advanced Research Projects Agency (DARPA) grant to build a qubit-based neutrino detector. |
A new project led by University of Chicago researchers will use “quantum sound” both to detect nuclear weapons and help uncover the fundamental nature of the universe.
UChicago Pritzker School of Molecular Engineering Prof. Andrew Cleland and Prof. Paolo Privitera of the Astronomy and Astrophysics Department and Physics Department are heading a team that recently received a $5 million Defense Advanced Research Projects Agency (DARPA) grant to build a qubit-based neutrino detector.
Neutrinos are abundant but very weakly interacting subatomic particles found everywhere from the sun to bananas. The process of creating the materials key to nuclear weapons emits neutrinos in huge quantities, and the ability to detect neutrinos could also shed light on dark matter, the mysterious and unknown stuff that makes up the bulk of the universe.
“There are clearly important applications to nuclear security, where the ability to detect if reactors are producing plutonium would be an important tool in slowing proliferation of the most dangerous nuclear weapons,” Cleland said. “However, I think more generally this will advance an area of science that could hold answers for what 90% of the matter in the universe actually is.”
The world’s best neutrino detectors are mostly sensitive to neutrinos above a few megaelectronvolts (MeV) of energy, fine for detecting solar flares and far-off supernovae, but not up to the task of finding dark matter or nations covertly building bombs. These detectors are also necessarily physically large—they can weight thousands of tons.
The DARPA QuSeN program that’s funding the research is calling for a much more compact one-kilogram detector, about a cubic meter in size, capable of sensing low-energy neutrinos down to perhaps 0.1 MeV.
“This is something that has never been done,” Privitera said. “There is no other detector that is able to detect neutrinos in the energy range that we are talking about.”
To take on a challenge that has never been done, Cleland and Privitera are taking an approach that has never been taken. They’re looking to detect low-energy neutrinos using phonons—micron-sized mechanical vibrations that at much larger scales would be considered sound.
Ghosts in the night
Neutrinos are lightweight, low-mass and weakly interact with other particles. They’re virtual ghosts in the subatomic world.
The common way to detect these ghosts is not to seek the neutrinos themselves, but to look for the interactions they create when they collide with atoms or molecules—extra electrons, muons, or nuclei where there shouldn’t be.
Uniting Cleland’s phonon research and Privitera’s explorations of dark matter, the team is looking to detect the collision itself, using powerful quantum sensors to detect the miniscule vibration induced by a single neutrino hitting an atom’s nucleus.
“The fundamental process is that the neutrino will get into your detector and basically will give a little kick to one of the nuclei in your detector material,” Privitera said. “The nucleus will recoil with a certain energy.”
By quantum entangling the phonon—not the particles that are vibrating but the motion itself, an area Cleland pioneered—the team hopes to create a sensor capable of “hearing” the small plink of a ghostly low-energy neutrino hitting an atom’s core.
But ghosts aren’t the only things that go bump in the night. To make sure the phonons they’re detecting are from neutrinos and not from neutrons, photons or other particles striking the nucleus, the team will research the vibrations those particles create when they hit a nucleus.
By knowing the “sound” of different particles hitting the nucleus, they’ll be able to subtract unwanted phonons from the signal, theoretically leaving only the quantum noise from neutrinos behind.
Challenges ahead
To explore the hidden nature of the universe, the detector will have to be sensitive at levels never before achieved by science.
To be practical for the type of weapons detection DARPA wants, the detector will be a few centimeters on a side, scaling to a cubic meter or so when including shielding, cryostat and other support machinery.
“DARPA always does things that are extremely ambitious,” Privitera said.
To take on this task, the project will involve researchers not only at UChicago but at Northwestern University, the Illinois Institute of Technology, the University of California-San Diego, and key partners at both Fermi National Accelerator Laboratory and Oak Ridge National Laboratory.
“This will be a very exciting project, melding the expertise of these different groups to build uniquely sensitive quantum devices that will have a wealth of applications in basic condensed matter physics, astrophysics and particle physics,” Cleland said.
This story originally appeared on the UChicago Pritzker School of Molecular Engineering website.