Researchers led by the Duke Quantum Center (DQC) have successfully used a quantum simulator to observe string breaking dynamics connected to particle-antiparticle formation, marking a significant milestone in the field of quantum physics and high-energy simulation.
The groundbreaking work, which was published on September 23 in Nature Physics, demonstrates how trapped-ion quantum computers are rapidly evolving into powerful tools for exploring some of the most profound and elusive questions in fundamental physics. In the experiment, the international research team simulated a complex physical process known as string breaking. This occurs when two connected building blocks of matter are pulled apart from one another until an immense amount of energy accumulates in the connection. Eventually, that stored energy becomes so high that new particles effectively "pop into existence" when the connection finally 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 University, who led the research initiative. "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 a wide-ranging international collaboration that brought together scientific expertise from the University of Maryland (UMD), Oxford University, the California Institute of Technology, Cornell University, and KU Leuven. Significantly, these findings appeared alongside two other recently published studies from separate, independent research teams that successfully reproduced similar fundamental physics using entirely different types of quantum computing hardware, highlighting a broad convergence in the capabilities of emerging quantum technologies.
Why Quarks Cannot Simply Be Pulled Apart
To understand the significance of the experiment, physicists look to the behavior of quarks, which rank among the most fundamental known building blocks of matter in the universe. Quarks are found tucked safely inside larger composite particles such as protons and neutrons, and they are roughly a billion times smaller than a standard atom. Because of the unique rules governing the subatomic realm, scientists cannot currently observe isolated quarks directly in nature. This is because quarks normally remain tightly bound together by the strong force, refusing to exist in a free, solitary state under normal laboratory conditions.
One intuitive way to picture this phenomenon is to imagine two tiny charged particles connected by a tightly stretched elastic string. As the particles are pulled farther and farther apart, the string stretches, and the tension increases dramatically. Consequently, more and more energy is stored directly in the connection binding them together.
Eventually, that localized tension reaches a critical threshold where enough energy accumulates to create additional charged particles out of the vacuum. This remarkable conversion is made possible by the fundamental equivalence of mass and energy, as described by Albert Einstein’s famous equation, $E=mc^2$. Rather than simply ending with one cleanly separated pair of original particles, the stretched connection snaps under the immense strain, and new particle-antiparticle pairs form in the aftermath to relieve the tension.
Under natural circumstances, processes of this magnitude require enormous amounts of energy. Ordinarily, they occur only under extreme, high-energy conditions, such as those intentionally created inside massive particle accelerators like the Large Headron Collider, or those believed to have universally existed just fractions of a second after the Big Bang.
Recreating String Breaking in a Quantum Machine
In the new experiment, the Duke-led team managed to bypass the need for a multi-mile particle collider by reproducing analogous string-breaking behavior safely inside a trapped-ion quantum platform. Quantum simulators are exceptionally well-suited for this type of demanding scientific work because researchers can exert precise control over their constituent parts, programming them to mimic complex physical processes that normally occur only at microscopic atomic and subatomic scales.
"Working at the intersection of quantum simulation and high-energy physics is incredibly exciting," said Arinjoy De, the first author on the published paper, a former PhD student in Monroe’s laboratory, and now a 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 construct the simulation, the researchers encoded a theoretical string-breaking model directly into a linear chain of 13 trapped ions. By applying carefully controlled laser beams to the system, the team was able to dynamically adjust how the individual ions interacted with one another in real time.
Those meticulously managed interactions allowed the researchers to control the overall energy of the system in a controlled manner that accurately reproduced the stretching, tension accumulation, and eventual breaking behavior characteristic of fundamental particle strings.
Watching the Quantum System Evolve
Once the physical architecture of the simulation was established, the researchers prepared the quantum system in an out-of-equilibrium state and then closely monitored how it changed and evolved over time. This meticulous observation allowed them to detect the appearance of effective charges and successfully reconstruct the complex dynamics associated with the simulated string-breaking process.
To rigorously verify their experimental results, the team also modeled the exact same physical process using a classical supercomputer. Pleasingly, the calculations generated by the classical computer aligned closely with the experimental results produced by the quantum simulator, validating the accuracy of the quantum approach.
However, researchers note that while classical computers can still easily perform the necessary calculations for simulations at this relatively small scale, that computational advantage will not last indefinitely. As future quantum experiments inevitably become larger, larger-scale simulations will grow exponentially more complex. The researchers expect that quantum computers will eventually reach a point where they can solve versions of these high-energy physics problems that classical machines can no longer handle.
The timing of this discovery coincides with parallel achievements by other prominent research groups in the field. Recently, separate teams led by Google and QuEra Computing successfully recreated related string-breaking models using superconducting circuits and neutral atom arrays, respectively. Each of these leading hardware platforms comes with its own distinct set of technical 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," Monroe added, emphasizing the cooperative spirit and competitive drive pushing the technology forward.
Toward Simulations Beyond Supercomputers
The successful trapped-ion results represent yet another significant stepping stone toward quantum simulations that are far too complex for even the world’s most powerful conventional supercomputers to process.
If quantum systems continue to scale up successfully in the coming years, researchers could eventually leverage them to investigate deep theoretical questions that are otherwise difficult or entirely impossible to reproduce directly in a physical laboratory setting. This includes unraveling the enduring mysteries of how matter behaved, interacted, and evolved during the fractions of a second immediately following 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, an associate professor of physics at UMD who was an integral part of the collaborative research team. "Even the slightest insights from an out-of-equilibrium physics model will guide us in the future."
The research was supported by funding and grants from the Department of Energy under awards DE-SC0020312, DE-SC0025341, DE-SC0019040, DE-SC0024220, and DE-SC0020271, as well as the National Science Foundation under award OMA-2120757. Additional support was provided by the Air Force Office of Scientific Research, the Defense Advanced Research Projects Agency, and Amazon Web Services.
