Classical Computers Match a Feat Claimed for Quantum Machines

Researchers used tensor networks — some on an ordinary laptop — to reproduce results a quantum computer was said to hold exclusively.

Researchers at the Simons Foundation's Flatiron Institute, working with collaborators at Boston University, used classical computers to simulate hundreds of interacting qubits arranged in square, cubic, and diamond-shaped lattices. Some of the calculations ran on a personal laptop. The work, published in Science with Joseph Tindall as first author and Miles Stoudenmire as a co-author, matched results a separate team had obtained on a quantum computer in a March 2025 Science paper — results that team had claimed a classical machine could not reproduce.

The method compresses the wave function describing the quantum system using tensor networks. The team drew on ITensor, a software library built at the CCQ, and applied belief propagation, an algorithm from the 1980s recently adapted for quantum systems. To handle three-dimensional dynamics, they built a 3D tensor network.

For the abundance question, the significance is where the work ran. If a laptop can approach problems assumed to need specialized quantum hardware, then a class of scientific computing becomes far cheaper and more widely accessible, lowering the cost of the research itself. That widens who can participate in this frontier.

What to watch is how far the approach scales. The researchers note belief propagation is more approximate than some alternatives, and their results were validated on smaller problems where correct answers could be checked. They frame classical and quantum computing as complementary rather than competing — so this redraws the boundary between the two, it does not erase it.

Source: ScienceDaily