Researchers at the Duke Quantum Center (DQC) have used a quantum simulator to watch string breaking dynamics tied to particle - antiparticle formation, marking one of the earliest demonstrations of its kind in quantum physics. The work, published September 23 in Nature Physics, suggests trapped-ion quantum computers could eventually serve as powerful tools for probing the deepest questions in fundamental physics. The experiment simulated string breaking: two connected building blocks of matter are pulled apart until enough energy accumulates that new particles effectively "pop into existence" when the connection snaps.
"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 the 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 an international collaboration including 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 quantum computing hardware.
Quarks are among the most fundamental known building blocks of matter. They live 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. Picture two tiny charged particles connected by a tightly stretched string: the farther apart they are pulled, the more energy is stored in the connection. Eventually, enough energy can accumulate to create additional charged particles - because mass and energy are related through Einstein's famous E=mc2. Rather than ending with one separated pair, the original connection breaks and new particle pairs form. Such processes require enormous energy and normally occur only under extreme conditions, like those inside the Large Hadron Collider or those believed to have existed shortly after the Big Bang.
In the new experiment, the Duke-led team reproduced analogous string breaking behavior using a trapped-ion quantum platform. Quantum simulators are especially useful here because researchers can precisely control and program them to imitate processes 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 adjusted how the ions interacted with one another. Those interactions let the team control the system's energy in a way that reproduced the stretching and eventual breaking of a particle-like string. The researchers prepared the system in an out-of-equilibrium state and followed how it changed over time, detecting the appearance of effective charges and reconstructing the dynamics associated with the simulated string breaking. To check the results, the team also modeled the same process on a classical computer, and the classical calculations agreed with the quantum simulator's experimental results.
For simulations at this relatively small scale, classical computers can still do the math. The researchers expect that as future experiments grow larger and more complicated, quantum computers will eventually solve versions of these problems that classical machines cannot handle. Other groups have recently hit similar milestones using different quantum hardware. Teams led by Google and QuEra Computing recreated related string breaking models using superconducting circuits and neutral atoms, respectively. Each approach has 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," Monroe added. The trapped-ion results represent another step toward quantum simulations too complex for even the world's most powerful conventional supercomputers. If quantum systems continue to scale up, researchers could eventually investigate questions that are difficult or impossible to reproduce directly in the lab - 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, DE-SC0019040, DE-SC0024220, DE-SC0020271), National Science Foundation (OMA-2120757), Air Force Office of Scientific Research, Defense Advanced Research Projects Agency and Amazon Web Services.
Materials provided by Duke University. Note: Content may be edited for style and length.