Physicists share a common interest in understanding how the physical world works. For example, when a particle physicist breaks apart a particle into smaller pieces, they ask themselves: are those the smallest pieces we can find in nature? For years, theoretical physicists have been limited to using classical computers, that is, computers that process information in 1s and 0s, as they explore the interactions between these small particles. Thanks to the power of quantum computers, which can encode numerous possible combinations of 1 and 0 simultaneously, physicists can create larger models that will potentially solve some of the most compelling puzzles in theoretical physics. 

However, theoretical researchers need access to novel computing technologies and a strong expert network for this new scientific endeavor. That’s where the Quantum Systems Accelerator’s catalyzing energy comes in. Since 2020, the Quantum Systems Accelerator (QSA), a U.S. Department of Energy (DOE) National Quantum Information Science (QIS) Research Center, has developed advanced quantum prototypes across major technologies to facilitate groundbreaking research in fundamental physics into the quantum world. Led by Lawrence Berkeley National Laboratory (Berkeley Lab) with Sandia National Laboratories as the lead partner, QSA brings together an ecosystem of 15 institutions in North America. With over 60 principal investigators, 130 staff, 91 postdocs, and 139 students, QSA advances national particle physics research by co-designing across institutions. 

Two teams of QSA researchers across partner institutions have recently made headway toward understanding more about the framework of the subatomic quantum world with quantum devices. One collaboration between Berkeley Lab and UC Berkeley, led by researchers Anthony Ciavarella and Christian W. Bauer, examined the dynamics between quarks and gluons, the tiny particles that comprise every atom’s core. Their published results build on previous studies supported by the QSA. They created a model to understand how these particles were held together (their nuclear force). They also wondered if a quantum computer could help them understand what would happen if quarks and gluons collided and broke into more particles. Using a theoretical understanding of these subatomic relationships, researchers built a model that mapped gluons onto a lattice for a quantum computer, marking the first time that anyone in this field has created such a model. 

Ciavarella and Bauer’s model will allow experimentalists to run simulations and compare these results to their experimental data. It will also help theorists take experimental results and, working backward, create a more robust theoretical underpinning for nuclear models. “If you want to search for new physics events where you produce Higgs bosons,” Ciavarella explains, “what you measure in [a particle accelerator] looks very similar to an event where you just have quarks and gluons radiating.” One day, simulations of Ciavarella and Bauer’s model can be used by experimentalists to reduce the size of background noise in their experiments and interpret results more clearly.

Thanks to QSA, Ciavarella and Bauer can soon run their model on a quantum computer. While the researchers worked on their paper, QSA staff helped them connect with researchers at Harvard University and Massachusetts Institute of Technology’s Center for Ultracold Atoms. The Harvard group has been building the type of hardware capable of running Ciavarella and Bauer’s proposed simulations. Ciavarella and Bauer are currently working with their colleagues to start running simulations this fall. “Once we can start doing these full simulations,” Ciavarella explains, “that should open up a whole new set of experimental observables that we’ve never really worked with because we’ve never been able to make predictions for them.”

Another multi-institutional QSA team has been investigating how one might use quantum processors to investigate models inspired by quantum chromodynamics (QCD). Using quantum processors to study the theories of the Standard Model in particle physics is a long-term goal of quantum simulation. While current quantum processors have not yet reached this capability, researchers have begun considering the required steps. Elizabeth Bennewitz, a researcher and graduate student at the University of Maryland, worked with other team members to develop a protocol for understanding the interactions between two mesons composed of tightly bound quarks. Bennewitz, the paper’s lead author in a recent preprint, is a DOE Computing Sciences Graduate (CSGF) Fellow and was formerly a Berkeley Lab intern. As a theorist, Bennewitz is interested in exploring what happens when mesons collide. However, running her simulations on a classical computer limits the number of interacting particles that theorists can study in a model. She worked with her collaborators to create a protocol that lists the necessary steps to build a model that would simulate the movement of mesons and what happens when those mesons collide. 

Their protocol will help experimentalists fill in the gaps as they try to create working models they can implement on quantum devices. Their work showed the types of meson scattering that might show up in a quantum device. By recognizing the byproducts of meson scattering, experimentalists can better interpret their results, distinguishing between irrelevant data (noise) and essential data (signal). This study represents one step towards using quantum processors as powerful tools to study quantum phenomena in particle physics and potentially extend the standard model of physics.

“Probing physics in these new ways will hopefully lead to discoveries in the physics side of things but can also influence other areas like material sciences and chemistry,” said Bennewitz.

Like Ciavarella and Bauer, Bennewitz’s team benefited from QSA’s support. Bennewitz has been struck by the interdisciplinary nature of QSA’s partners and its ability to connect researchers across different areas with relevant collaborators. 

“Being able to work really closely with experts in quantum simulation, high-energy and nuclear physics, and experimental quantum devices was one of the reasons this work was possible,” said Bennewitz.

Both QSA teams voiced how working with new colleagues helped them consider new dimensions of planning an experiment. 

“Something that might be obvious to them when they’re just looking at the experiments up in the lab might not be obvious to me because I’ve never worked directly in the lab on a device myself and vice versa, with how to map problems on their computers. It’s a way to learn a lot about interesting things,” said Ciavarella. 

The work of these QSA researchers has underscored the importance of quantum simulators as a tool for investigating the almost invisible subatomic world of particle physics. By bringing together experimentalists and theorists, QSA continues to facilitate research by streamlining the design of quantum devices and engineering solutions. Moreover, QSA provides early career researchers like Ciavarella and Bennewitz with the infrastructure and support to conduct their studies. 

“There’s a lot of evidence that studying these models on quantum computers and quantum simulators should be more powerful for certain types of problems. With quantum simulations, we can unveil and probe particle physics in ways that we haven’t been able to before and hopefully find new physics,” said Bennewitz.

QSA director Bert de Jong believes that, in the coming decade, even more researchers like Bennewitz will embrace quantum computers as an investigative tool. “We have a high-energy physics team in the QSA team that would like to build better theories to understand the foundational building blocks of the universe,” concluded de Jong.