Simulation Breakthrough: Classical Computers Tackle "Quantum-Only" Problem
Physicists at the Center for Computational Quantum Physics (CCQ) at the Simons Foundation’s Flatiron Institute, working with collaborators at Boston University, have successfully simulated the dynamics of hundreds of interacting qubits arranged in three-dimensional lattices—using nothing more powerful than conventional computers, including a personal laptop.
This work demonstrates that a problem previously claimed to be solvable only by quantum computers can be tackled with classical methods and advanced tensor network algorithms.
Key Details of the Study
- The Technique: Researchers employed tensor networks, a compression method for the wave function that drastically reduces computational requirements.
- The Hardware: Initial calculations were performed on a standard laptop utilizing the ITensor software library, developed at CCQ.
- The Algorithm: The team adapted a method called belief propagation for quantum systems. This approach is significantly less resource-intensive than traditional alternatives.
- The Results: The simulations achieved accuracy that matched both theoretical predictions and results previously obtained from quantum computers.
- Publication: The findings were published in Science on May 21, 2025.
Context: Challenging a "Quantum Supremacy" Claim
In March 2025, a separate group published a paper in Science stating they had calculated the dynamics of a qubit system using a quantum computer, claiming the task was impossible for classical computers. The CCQ team viewed this as a direct challenge and an opportunity to rigorously test their own tools. The core difficulty arises from quantum entanglement, which prevents qubits from being treated independently, making simulation exponentially complex.
A Deeper Look at Tensor Networks
Tensor networks function by compressing the exponentially expanding wave function into a set of interconnected tables of numbers. While this technique is well-established, working with tensor networks in three dimensions remains a frontier field, requiring sophisticated algorithms and software to navigate the immense complexity.
Statements from the Research Team
Joseph Tindall (CCQ): "Whenever we see these kinds of claims, we're always a bit skeptical."
Miles Stoudenmire (CCQ): "We could have picked some more arbitrary target, but it was like 'Why not pick this one that has a big claim attached to it?'"
Tindall further explained that while the belief propagation method is approximate, it is computationally cheaper and can be applied directly to more difficult problems. Stoudenmire added that older, more sophisticated methods "wouldn't be able to even start going for some of these three-dimensional problems, because they're so big."
Broader Significance
This work highlights the powerful and ongoing synergies between classical and quantum computing research. The methods developed here are not merely a rebuttal to a single claim; they may prove crucial for simulating electrons in real materials—a far more complex and practically important challenge.
The Flatiron Institute is the research division of the Simons Foundation, dedicated to advancing computational science.