Building the quantum toolbox

• QuantISED supports the development of quantum technologies aimed at addressing fundamental questions in physics, including the nature of dark matter and the connection between quantum mechanics and gravity.
• In Phase 1, researchers built and demonstrated new types of quantum detectors and devices that can operate in areas of physics that were previously hard to explore.
• In Phase 2, the focus shifts to using these tools in real experiments, with the goal of expanding dark matter searches and exploring new ways to test fundamental ideas about the universe.

From the search for dark matter to the test of ideas about quantum gravity, the exploration of today’s biggest physics questions requires technologies that don’t yet exist. Answering them isn’t just about making better measurements – it’s about inventing entirely new ways to sense, control and manipulate quantum systems.

That’s the goal of Quantum Information Science Enabled Discovery (QuantISED), a Department of Energy (DOE) High Energy Physics program launched in 2018. The program brings together researchers across disciplines to develop quantum technologies capable of exploring some of the universe’s biggest unanswered questions.

As the program enters its next phase, QuantISED 2.0, scientists at the DOE’s SLAC National Accelerator Laboratory and Stanford University are reflecting on what the first round made possible and what comes next.

Bridging the gap

For Emilio Nanni, an associate professor of particle physics and astrophysics and of photon science at SLAC, the challenge begins with a part of the electromagnetic spectrum that few quantum sensors can reach. 

“There’s no single sensor that works across all frequencies,” he said. “Quantum transducers are especially powerful because they convert signals into frequencies where sensors perform best.”

In the program’s first phase, the team pursued two complementary strategies. One focused on superconducting devices designed to connect microwave and millimeter-wave frequencies – work that remains ongoing. The other led to a major milestone: a chip-scale device that converts millimeter waves into optical light while approaching fundamental quantum limits.

“This is the first chip-scale frequency converter to approach quantum limits,” Nanni said.

By the end of this phase, he added, “we expect to have sensors operating in frequency regimes that have been extremely challenging to probe.”

Harnessing quantum bits

For SLAC scientist Noah Kurinsky, QuantISED began as an extension of work in his lab focused on building sensors out of qubits, the same devices used in quantum computers.

To make that happen, his group has been building the pieces needed to test that idea: not just qubit-based sensors, but the infrastructure required to calibrate them. A key effort involves developing a tunable terahertz photon source capable of delivering controlled signals into a dilution refrigerator, where the sensors operate just above absolute zero. At those temperatures, even tiny imperfections matter. 

“For the full system to work, it’s basically several different projects that all have to succeed,” Kurinsky said. “But we have early results on each component, and they’re promising.”

The long-term goal is to build a tunable source of single terahertz photons that can be steered across a detector, so the team can see exactly how it responds. The detector needs to be extraordinarily quiet, registering at most about one false signal per day. 

“That’s a huge experimental challenge,” Kurinsky said. “But if any of this works even remotely well, it opens a largely unexplored window of the electromagnetic spectrum, giving us new ways to search for signals we couldn’t access before.”

The first major application is axion dark matter. Kurinsky’s group is involved in the Broadband Reflector Experiment for Axion Detection (BREAD), a tabletop axion search that aims to scan large regions of unexplored parameter space without the need for massive underground detectors. A reliable single-terahertz-photon source could significantly speed up that search. 

While dark matter is the immediate motivation, the implications extend further. Terahertz sensing has potential applications in areas ranging from materials science to non-ionizing biomedical imaging. Kurinsky sees dark matter searches as an opportunity to push detector technology to its limits in ways that often spill over into other fields.

“One way I think about dark matter searches is that they force detector technology to its absolute limits,” he said. “And then those technologies find broader applications.”

In QuantISED 2.0, Kurinsky hopes to move beyond early demonstrations into real measurements.

“Right now, each group has shown that the basic devices work,” he said. “The next step is putting them in front of a real signal and seeing what they can do.”

“Long term, I’d love for this work to help build a durable program at SLAC where we’re a major player in terahertz sources and detectors, with applications in health, defense and more,” he added. “In the short term, if we find dark matter, that would be a pretty exciting bonus.”

Listening for dark matter

At the opposite end of the spectrum, Kent Irwin, a professor of physics at Stanford and professor of photon science and of particle physics and astrophysics at SLAC, is pursuing a different strategy.

Instead of counting photons in the terahertz range, his team is working below a gigahertz, a frequency range where some of the best-motivated axion dark-matter models lie.

At those low frequencies, he says, the rules change.

“Below a gigahertz, you don’t want to use the same quantum technologies used at higher frequencies,” Irwin said.

At higher frequencies, experiments often try to detect individual photons. That strategy makes sense when photons are sparse and can be counted one by one. But at lower frequencies, thermal background photons are unavoidable, even at extremely low temperatures.

“You don’t want to count photons,” Irwin said. “You want something more like a radio: a quantum radio.”

The approach reflects how dark matter behaves at different mass scales. At very low masses, axions would behave less like a stream of individual particles and more like a faint, continuous wave filling all space. Detecting them is less like waiting for a rare particle collision and more like tuning a radio to an unknown station.

QuantISED 2.0 will rely heavily on SLAC’s new superconducting-focused Device Microfabrication Facility (DMF), which will enable more complex, multilayer quantum devices.

“We’re at the point where the sensors work and we understand them,” Irwin said. “Now we’ll have the fabrication tools to optimize and integrate them. That’s when the really fun part begins.”

Looking further ahead, Irwin sees this effort as part of a larger shift in particle physics. Decades of searches for Weakly Interacting Massive Particles (WIMPs), a hypothesized dark matter candidate, have ruled out large regions of parameter space. Axions remain one of the most compelling alternatives.

“If axions exist, they should be produced in abundance,” Irwin said. “The community ultimately needs to search the full mass range.”

He argues that SLAC’s distinctive contribution has been leadership in the lower-frequency regime, territory that relatively few experiments are exploring.

“This is laying the groundwork for a large-scale effort,” Irwin said. “Something SLAC could potentially lead.”

Probing quantum gravity

Another effort, led by Stanford physicist Monika Schleier-Smith, tackles a different frontier: the relationship between quantum mechanics and gravity.

This setup produces interactions that connect distant atoms, rather than only neighboring ones.

“In our lab, photons provide a communication channel,” Schleier-Smith said. “They allow information to move between atoms that aren’t directly next to each other.”

Those engineered interactions let the team study how quantum information spreads, or “scrambles,” across a system, an idea that also appears in discussions of black holes.

During the first phase of QuantISED, they arranged the atoms so they interacted in a specific way and then measured how information spread through the system. When they analyzed the data, a branching, tree-like pattern emerged – one that physicists recognize as a simple model of curved space.

“That was a highlight of our work,” Schleier-Smith said. “It demonstrated a concrete way in which geometry can emerge as a description of correlations in a quantum system. Properties that look like features of space appeared not from the hardware itself, but from patterns of entanglement.”

Looking ahead to QuantISED 2.0, the goal is to move beyond proof-of-principle demonstrations toward true quantum simulation – experiments that explore regimes too complex for classical computers to predict.

“Ideally, we want to reach a regime where we build the system, run the experiment and learn something we couldn’t have calculated beforehand,” Schleier-Smith said.

This requires dramatically stronger interactions between single atoms and photons. Achieving that will involve a new experimental platform developed in collaboration with Nanni’s group: a superconducting millimeter-wave cavity operating at cryogenic temperatures. Unlike previous experiments, where the atoms were ultracold while the apparatus remained at room temperature, this new cavity itself must be cold and superconducting.

“This new platform could improve the coherence of atom–photon interactions by orders of magnitude,” Schleier-Smith said. “It opens the door to exploring entirely new quantum regimes.”

Phase 2 will also expand the theory collaboration. Schleier-Smith’s project now includes theorists at Stanford and beyond who specialize in quantum information and quantum gravity, strengthening the connection between cutting-edge theory and experiment.

“In Phase 1, a lot of the work was building the toolbox,” she said. “Now we’re really aiming to connect those theoretical ideas with experiments in a deeper way.”

Putting the tools to the test

While the first round of QuantISED focused on demonstrating that new quantum technologies could work at all, the emphasis is shifting toward integration, optimization and real experiments – the stage where new physics may emerge.

“We’re transitioning from developing the technology to actually turning it into sensors that can be used for physics,” Nanni said.

If successful, the advances made through QuantISED could expand dark matter searches, open new frequency windows for observation and create laboratory systems that explore how gravity and quantum mechanics are connected.

“These are difficult problems,” Kurinsky said. “But if we can build the right tools, we can start to answer them.”

This research is supported by the Department of Energy’s Office of Science. The list of projects and more information can be found on the High Energy Physics program homepage.