How quantum computers can be validated when solving unsolvable problems
by Simon Mansfield
Melbourne, Australia (SPX) Sep 17, 2025

Quantum computers are designed to tackle challenges that would take even the fastest supercomputers thousands or millions of years to resolve. But this raises a central paradox: how can researchers verify the correctness of results that classical machines cannot reproduce?

A team at Swinburne University of Technology has developed new methods to validate outcomes from a class of quantum computers called Gaussian Boson Samplers (GBS). These devices use photons to calculate probability distributions, computations that would otherwise take millennia to complete on existing high-performance machines.

"Therefore, in order to validate quantum computers, methods are needed to compare theory and result without waiting years for a supercomputer to perform the same task," explained Alexander Dellios, lead author and postdoctoral research fellow at Swinburne's Centre for Quantum Science and Technology Theory.

The group's approach enables researchers to determine in minutes on a standard laptop whether a GBS device is producing the intended distribution and to identify errors. When applied to a recent GBS experiment that would require at least 9,000 years to simulate classically, the method revealed discrepancies: the observed output did not match the expected distribution, with extra noise affecting the result.

The team is now investigating whether the alternative distribution observed is still computationally hard to simulate or whether the errors diminished the device's quantum properties. Resolving this will guide the path toward error-free quantum computers at scale.

"Developing large-scale, error-free quantum computers is a herculean task that, if achieved, will revolutionise fields such as drug development, AI, cyber security, and allow us to deepen our understanding of the physical universe," said Dellios. "A vital component of this task is scalable methods of validating quantum computers, which increase our understanding of what errors are affecting these systems and how to correct for them, ensuring they retain their 'quantumness'."

Research Report:Validation tests of Gaussian boson samplers with photon-number resolving detectors

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