In a new study, researchers from the Flatiron Institute’s Center for Computational Quantum Physics (CCQ) have developed an understanding of the unique boundaries between classical and quantum computing. In January 2024, they achieved an unexpected result: using a classical computer to outperform a quantum computer on a problem previously believed to be unsolvable without quantum technology.
“This unexpected finding is helping scientists better understand the line dividing the abilities of quantum and classical computers and provides a framework for testing new quantum simulations,” lead researcher Joseph Tindall noted.
The research team’s success came while tackling a two-dimensional system of flipping magnets—a highly complex problem initially assumed to require quantum computing. Typically, quantum computers hold an edge in such scenarios due to entanglement, where particles become deeply interconnected. Entanglement’s growth usually makes quantum systems challenging for classical computers to simulate.
However, the researchers observed a unique phenomenon called “confinement.” Normally seen in one-dimensional systems, confinement restricts energy within the system, limiting how much entanglement can grow and thus making it feasible for a classical computer to simulate.
“There is some boundary that separates what can be done with quantum computing and what can be done with classical computers… our work helps clarify that boundary a bit more,” Tindall explained.
Interestingly, this new boundary emerged after IBM researchers claimed in June 2023 that only a quantum computer could solve a similar complex simulation. Tindall and his team, however, solved it using a classical computer in just two weeks. “We didn’t really introduce any cutting-edge techniques,” Tindall stated. “We brought a lot of ideas together in a concise and elegant way that made the problem solvable.”
This breakthrough offers a new framework for testing quantum simulations and suggests confinement might exist in other two-dimensional systems, leading to more focused research into when and how entanglement grows within quantum systems.
“This experiment gives us a good understanding of an example where we don’t get large-scale entanglement due to the model used and the two-dimensional structure of the quantum processor,” Tindall added.