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🧬 A landmark experiment with quantum computers has put an end to a century-old debate: is the wave function a real part of nature, or just a tool for prediction?

Physicists have long puzzled over the wave function in quantum mechanics. Is it simply a mathematical trick to describe probabilities, or does it represent something physically real? A new experiment led by Songqinghao Yang and colleagues at the University of Cambridge has now put this question to the test, using IBM’s advanced 156-qubit Heron quantum computer.

The team implemented the Pusey-Barrett-Rudolph (PBR) theorem, a rigorous test designed to distinguish between two views: the ontic (wave function is real) and epistemic (wave function is just knowledge about reality). By preparing qubits in specific, non-orthogonal states and evolving them through carefully controlled circuits, they observed the system’s outcomes, even accounting for hardware noise and imperfections.

Their results revealed that, for small sets of qubits, the predictions of quantum theory hold true. The wave function directly reflects reality, decisively ruling out “hidden variable” alternatives—at least at the scales tested. Notably, the accuracy of the test depended on the connectivity and coherence of the qubits, declining for more distant pairs—highlighting the impact of technical noise in current quantum machines.

This experiment doesn’t just settle a foundational question; it provides a valuable new benchmark for verifying the “quantumness” of future quantum computers. As quantum devices evolve, such tests will be vital in probing the true nature of reality—and in paving the road to practical quantum technologies.

📄 RESEARCH PAPER

📌 Songqinghao Yang et al, "Experimental Demonstration of the PBR Test on a Superconducting Processor", arXiv (2025)

Image: Andrzej Wojcicki / Science Photo Library