Researchers led by the Duke Quantum Center (DQC) have used a quantum simulator to observe string breaking dynamics connected to particle antiparticle formation, marking one of the earliest demonstrations of its kind in quantum physics.
The work, published September 23 in Nature Physics, shows how trapped ion quantum computers could become powerful tools for exploring some of the deepest questions in fundamental physics. The experiment simulated a process known as string breaking, in which two connected building blocks of matter are pulled apart until so much energy accumulates that new particles can effectively “pop into existence” when the connection breaks.
“Quantum computer simulations provide the best platform to investigate complex questions like matter formation, short of having witnessed the Big Bang itself,” said Christopher Monroe, the Gilhuly Family Presidential Distinguished Professor of Electrical and Computer Engineering and Physics at Duke, who led this research. “These findings signal a marked development in the quantum science field and open new avenues for us to understand string-breaking dynamics.”
The study was carried out by an international collaboration that included researchers from the University of Maryland (UMD), Oxford University, California Institute of Technology, Cornell University and KU Leuven. The findings appear alongside two other recently published studies from separate teams that reproduced similar physics using different types of quantum computing hardware.
Why Quarks Cannot Simply Be Pulled Apart
Quarks are among the most fundamental known building blocks of matter. They are found inside particles such as protons and neutrons and are roughly a billion times smaller than an atom. Scientists cannot currently observe isolated quarks directly because quarks normally remain tightly bound together.
One way to picture this is to imagine two tiny charged particles connected by a tightly stretched string. The farther apart they are pulled, the more energy is stored in the connection between them.
Eventually, enough energy can accumulate to create additional charged particles. This is possible because mass and energy are related through Einstein’s famous equation E=mc2. Rather than ending with one separated pair, the original connection breaks and new particle pairs form.
Such processes require enormous amounts of energy and normally occur only under extreme conditions, such as those created inside the Large Hadron Collider or those believed to have existed shortly after the Big Bang.
Recreating String Breaking in a Quantum Machine
In the new experiment, the Duke-led team reproduced analogous string breaking behavior using a trapped-ion quantum platform. Quantum simulators are especially useful for this kind of work because researchers can precisely control them and program them to imitate physical processes that occur at atomic and subatomic scales.
“Working at the intersection of quantum simulation and high-energy physics is incredibly exciting,” said Arinjoy De, first author on the paper, former PhD student in Monroe’s lab and now production machine lead at QuEra Computing. “By simulating quark confinement and string-breaking phenomena in a controlled lab environment, we’re opening up new pathways for experimental investigations into the behavior of matter at its most fundamental level.”
To build the simulation, the researchers encoded a string breaking model into a chain of 13 trapped ions. Carefully controlled laser beams were then used to adjust how the ions interacted with one another.
Those interactions allowed the team to control the system’s energy in a way that reproduced the stretching and eventual breaking of a particle like string.
Watching the Quantum System Evolve
The researchers prepared the system in an out of equilibrium state and then followed how it changed over time. This allowed them to detect the appearance of effective charges and reconstruct the dynamics associated with the simulated string breaking process.
To check the results, the team also modeled the same process using a classical computer. The classical calculations agreed with the experimental results produced by the quantum simulator.
For simulations at this relatively small scale, classical computers can still perform the calculations. The researchers expect that as future experiments become larger and more complicated, however, quantum computers will eventually be able to solve versions of these problems that classical machines cannot handle.
Other research groups have recently reached similar milestones using different forms of quantum hardware. Teams led by Google and QuEra Computing recreated related string breaking models using superconducting circuits and neutral atoms, respectively. Each approach comes with its own strengths and limitations.
“These are the three platforms leading the charge in quantum computing, so it’s a nice benchmark and comparison for the quantum community,” added Monroe.
Toward Simulations Beyond Supercomputers
The trapped ion results represent another step toward quantum simulations that are too complex for even the world’s most powerful conventional supercomputers.
If quantum systems continue to scale up, researchers could eventually use them to investigate questions that are difficult or impossible to reproduce directly in the laboratory, including how matter behaved and evolved shortly after the Big Bang.
“As a physicist, it is incredibly exciting to investigate the conditions of the early universe in an atomic-level computing machine,” said Zohreh Davoudi, associate professor of physics at UMD, who was part of the research team. “Even the slightest insights from an out-of-equilibrium physics model will guide us in the future.”
The research was supported by the Department of Energy (DE-SC0020312, DE-SC0025341, DESC0019040, DE-SC0024220, DE-SC0020271), National Science Foundation (OMA-2120757), Air Force Office of Scientific Research, Defense Advanced Research Projects Agency and Amazon Web Services.
