Quantum computer simulates hadronization, reproducing string breaking with 104 qubits Stephanie Baum Scientific Editor Robert Egan Senior Editor By remotely accessing an IBM quantum computer, a research scientist at Lawrence Berkeley National Laboratory has successfully simulated a key process in particle physics: hadronization. Although based on a simplified model of quantum mechanics, the project lays the groundwork for how physicists can leverage the power of quantum computers to make large scientific calculations beyond the capabilities of classical supercomputers. The research is published in the journal Physical Review D.

Hadronization occurs when two or more quarks—the subatomic building blocks of matter—bind together through the strong nuclear force to form composite particles called hadrons. The most familiar examples of hadrons are protons and neutrons, which form the nuclei of atoms. So, having a better understanding of the hadronization process means having a better understanding of the structure of matter, and—in turn—the universe.

Physical experiments have not been able to reveal every step of the process, however. Researchers at the Large Hadron Collider (LHC) at CERN accelerate protons to near light speeds, guide them into collisions and study the resulting debris of quarks and antiquarks. But these particles can only be indirectly measured before they immediately undergo hadronization—hence the need for computer simulations to fill in the gaps of these scientific observations.

"In principle, we know the theory that describes hadronization, but we are unable to make predictions using it because the calculations have been too difficult for a classical computer. However, on a quantum computer, we should be able to directly make predictions for the details of how hadronization occurs, which will help with the searches for new physics performed at colliders such as the LHC," said Anthony Ciavarella, the Berkeley Lab research scientist who led the project. Where classical computing hits a wall Quantum computing—a technology still in the early stages of development relative to classical supercomputers such as the OLCF's exascale-class Frontier—utilizes quantum bits, or qubits, to perform calculations.

Unlike binary bits used by classical computers, qubits don't employ only ones and zeroes to encode information. Rather, they use a quantum superposition of combined ones and zeroes that may exponentially increase processing power for certain kinds of problems, such as the quantum mechanical interactions of subatomic particles. Accurately simulating quantum chromodynamics (QCD)—the theory describing how the strong force binds quarks and gluons—overwhelms classical computers.

The strong force binds and entangles the subatomic particles so that their representation and manipulation on classical computers requires exponential amounts of processing power and memory to predict observable results. This is because binary computers must separately represent all the different possible quantum states of the particles, which becomes an exponential scaling problem—the amount of memory needed doubles for every new particle or time step added to the simulation.