For decades, scientists have battled to describe dark matter, which makes up a quarter of the universe. As investigations continue to come up empty-handed, one group is hoping to uncover dark matter by combining the equations that control subatomic particles—quantum mechanics—with a fledgling type of technology known as a quantum computer. It’s what drew Fermilab scientist Daniel Bowring, who has a background in accelerator physics, to partner with David Schuster’s quantum computing lab at the University of Chicago.“The first time I went in there, I felt like Charlie entering Willie Wonka’s factory,” he said.
The experiment lab is now located at Fermilab, just outside of Batavia, Illinois, in a high-ceilinged room with all-white walls and a dark tower of physics equipment at the bottom of a warehouse stairway, separated by glass separators. A tower of electronics with flashing lights and a table with a computer monitor sat against the far wall when I visited Fermilab in January, alongside a person-sized silver cylinder hanging from a steel rack, known as a dilution refrigerator, which keeps superconducting components functioning at just above absolute zero. As the refrigerator pumped its liquid helium, the room resonated with a rhythmic shriek, and Bowring, Fermilab research associate Rakshya Khatiwada, and University of Chicago graduate students Akash Dixit and Ankur Agrawal demonstrated how it operated. Although Bowring despises acronyms, it’s named QISMET, which stands for Quantum Information Science Metrology.
Quantum computers are currently limited in their capabilities, excelling only in a few contrived algorithms used mostly as random number generators, yet their creators hope that one day these machines will solve problems that normal computers cannot. However, due to sensor limitations, one dark matter-hunting team decided to develop a dark matter detector using the same components as a quantum computer. Their device, which is currently being built at Fermilab, cements extreme sensing as one of quantum technology’s strongest real-world applications. Typical dark matter studies are carried out in severe environments like the International Space Station and deep beneath mountains, where scientists use tonnes of liquid xenon, sapphire crystals, and colliding particles to look for signs of new particles. The most prominent candidate for explaining all of the extra gravity is a new class of fundamental particles known as weakly interacting massive particles, or WIMPs, which barely interact with conventional matter. While searches for WIMPs continue to yield no results, other researchers have been looking for the axion, a hypothetical fundamental particle named after a laundry detergent.
QISMET suffers from the same issue that other quantum computers do, explained Dixit. “We know qubits can count photons, but they also make a lot of mistakes,” he said. “We want to know how to take all of these mistakes into account.” That includes keeping the cavity as empty as possible and storing the axion’s photon for as long as feasible, as well as ensuring that researchers are aware of the possibility of the qubit unexpectedly flipping to the excited state unintentionally. Chou said in an email that the team could take another year to work out the flaws in the project.
Other dark matter investigations have begun to include quantum intuition, such as the axion-hunting HAYSTAC experiment and Fermilab scientist Alex Romanenko’s Dark SRF experiment, which aims to make a dark matter candidate in a superconducting radiofrequency cavity and detect it in another. According to Fermilab deputy chief technology officer Anna Grasselino, “pursuing these experiments has pushed these two fields forward hand-in-hand.” “I would say the technology is pushing the search forward, but the search itself is motivating us to investigate quantum technology further,” she said. Most firms focusing on constructing quantum computers don’t worry about qubit mistakes at the same level as the QISMET team, which requires some of the lowest error rates in the industry. Workforce development is one of the most difficult aspects of organizing a fundamental research experiment like this, according to Bowring. IBM, Google, Intel, Microsoft, and other multibillion-dollar corporations are all pursuing quantum technologies in a field with a small pool of qualified candidates. Bowring can pay an applicant about to graduate grad school the income of a post-doctoral researcher, but a tech firm can pay several times that.“We can only go as fast as we have staff power for,” he said.
However, once QISMET is up and running, it will show how quantum technology outperforms traditional sensing methods, most likely before Google and IBM’s quantum computers have useful computational applications. The discovery highlights the value of basic research in pushing the boundaries of technology to solve challenges that only physicists can solve, such as how to find a subatomic particle that may or may not exist. The experiment’s scientists are motivated by the tremendous, enigmatic force of curiosity, not by the desire to manufacture a product that might one day generate a profit.
