Quantum simulator captures a strange process that can break quark strings

A quantum simulator has given physicists a new look at one of the strangest processes predicted by particle physics.

What happens when the invisible string connecting two fundamental particles—a quark and its antimatter counterpart, an antiquark—is stretched so far that new particles can begin to form?

Researchers recreated this underlying dynamics in a controllable quantum system and found that string breaking can begin at the edges before spreading inward.

This result reveals a mechanism distinct from the conventional picture of particle-antiparticle production and could offer a new way to study phenomena that are otherwise difficult to calculate.

“These findings signal a marked development in the quantum science field and open new avenues for us to understand string-breaking dynamics,” Christopher Monroe, one of the study authors and a professor at Duke University, said.

A string that can create new particles

The idea comes from quantum chromodynamics, the theory describing the strong force. Quarks carry a type of charge called color charge and are never found alone. They remain confined inside particles such as protons and neutrons.

When a quark and antiquark are pulled apart, the energy between them does not simply weaken with distance. Instead, it increases as a gluon field forms a flux tube, often pictured as a string connecting the two.

If enough energy accumulates, it can become energetically favorable to create another quark-antiquark pair, effectively fragmenting the original string.

Studying these dynamics directly is difficult because calculating their real-time evolution becomes increasingly demanding for classical computers, particularly as the system develops substantial quantum entanglement.

The new experiment offered a way to examine related dynamics in a controlled quantum system without attempting to reproduce the full complexity of real-world quantum chromodynamics.

Turning a gauge theory into a quantum experiment

To recreate the physics of quark confinement in a manageable laboratory system, the researchers used a simplified one-dimensional model of a gauge theory called a Z₂ lattice gauge theory on a programmable trapped-ion quantum simulator.

Unlike the full theory of the strong force, which operates in three spatial dimensions, this model reduces the problem to a one-dimensional chain while retaining key features such as charges, strings, and confinement.

The researchers then converted this gauge theory into an equivalent quantum spin model that could be implemented with trapped ions and controlled using laser beams. In this mapping, a particle-like charge appears as a “kink” between differently oriented spins, while the electric-field string becomes a region of spins pointing in the opposite direction.

The experiment used a 15-ion chain, but only the 13 central ions were actively driven and included in the simulated system. Precisely controlled laser beams programmed interactions between the ions, while another set of tightly focused beams controlled local magnetic fields.

This allowed the researchers to create the equivalent of static charges and strings and then suddenly change the system’s conditions. Before studying a complete string, the researchers tested how an isolated effective charge moved through the simulated system.

With little or no string tension, the charge spread freely through the chain. As the tension increased—the energy stored in the simulated string per unit length—the charge became confined and underwent localized, coherent oscillations.

The researchers then prepared a simulated string stretched between two static charges and abruptly increased its tension, pushing the system far from equilibrium. By tracking the charge distribution across the chain and over time, they found that new effective charge pairs appeared preferentially near the two ends of the string.

At weaker tension, these pairs remained concentrated near the edges and oscillated. At stronger tension, they propagated away from the edges and spread toward the center. This behavior differs from the conventional Schwinger mechanism, in which strong fields produce particle-antiparticle pairs throughout the bulk.

The researchers’ analysis suggests that the sudden change in the simulated system first creates a quantum superposition of charge pairs near the string’s edges. Those pairs can then move through the system according to quantum dynamics.

What the experiment means for physics

The experiment does not show real quarks being produced, nor does it reproduce the full three-dimensional physics of the strong force.

Instead, it demonstrates that a programmable trapped-ion system can reproduce and resolve the real-time behavior of a related gauge theory closely enough to reveal an unexpected string-breaking mechanism.

The next step is to make the simulated environment more realistic. The researcher plans to investigate setups involving probe charges that move apart, as well as fully dynamical strings and their surrounding environments.

Such experiments could help determine whether the edge-driven mechanism has broader relevance to high-energy collisions and the evolution of the early universe.

“Working at the intersection of quantum simulation and high-energy physics is incredibly exciting. 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,” Arinjoy De, first author of the study, said.

The study is published in the journal Nature Physics.