Superconducting Processor with 156 Qubits Demonstrates Violation of Epistemic Interpretation of Mechanics

The fundamental nature of quantum mechanics, and whether it reflects a deeper reality or simply our limited knowledge of it, remains a central question in physics. Songqinghao Yang, Haomu Yuan, and Crispin H. W. Barnes, all from the University of Cambridge, now present experimental evidence addressing this question, by directly testing a key prediction of the Pusey-Barrett-Rudolph (PBR) theorem. The team implements the PBR test on a 156-qubit superconducting processor, carefully preparing qubits and evolving them with precisely controlled circuits, and accounts for the imperfections inherent in current quantum hardware. Their results demonstrate a clear violation of the idea that quantum states merely represent our lack of information, and reveal that the test’s success diminishes as the distance between qubits increases, offering a valuable new benchmark for assessing the performance of noisy quantum processors.

Ontic Quantum States Experimentally Verified

This research team successfully implemented the Pusey-Barrett-Rudolph theorem on a 156-qubit superconducting processor, representing a significant step towards experimentally testing fundamental interpretations of quantum mechanics. By preparing qubits in specific non-orthogonal states and evolving them using carefully designed circuits, the scientists investigated whether quantum states merely reflect a lack of knowledge about an underlying physical reality. The results demonstrate a clear violation of this “epistemic” interpretation for a majority of adjacent and closely-connected qubits, supporting the idea that quantum states possess an ontic, or reality-based, nature. The team accounted for the imperfections inherent in current quantum hardware, deriving and verifying noise-dependent bounds to quantify when experimental results definitively exclude these epistemic models.

These bounds allowed the scientists to determine the limits of explanations based solely on incomplete knowledge, ensuring the validity of the findings despite the presence of realistic noise. Importantly, the study revealed that the probability of successfully passing the PBR test decreases as the physical separation between qubits increases, highlighting the sensitivity of this protocol to connectivity and coherence within noisy intermediate-scale quantum systems. Future research could extend these tests to larger systems or explore different quantum states, potentially providing valuable benchmarks for assessing the performance and “quantumness” of emerging quantum devices and further defining the path towards practical quantum advantage. The findings contribute to a deeper understanding of the fundamental nature of quantum reality and its implications for future quantum technologies.

PBR Theorem Tested on Superconducting Qubits

Scientists successfully implemented the Pusey-Barrett-Rudolph (PBR) no-go theorem on a 156-qubit superconducting processor, investigating whether quantum states reflect only our knowledge of an underlying reality or represent physical reality itself. By preparing qubits in specific non-orthogonal states and evolving them using carefully compiled circuits, the scientists investigated the limits of explanations based solely on incomplete knowledge. Measurements confirm that the protocol remains viable even when leveraging the full spatial extent of the processor, rather than limiting the experiment to locally connected qubits. To account for realistic hardware imperfections, the team developed a noise-aware error tolerance based on decoherence models calibrated to the device’s performance, combining a depolarizing error model with measurements of T1 and T2times.

This dual-model strategy enabled determination of new error tolerances, revealing the conditions required for successful protocol execution under realistic conditions. The study revealed that a significant majority of tested configurations violate the bounds predicted by epistemic models, suggesting that the observed quantum behavior cannot be fully explained by simply assuming our knowledge of the system is incomplete. This establishes the PBR test as a promising device-level benchmark for evaluating the performance of quantum computers and probing the foundations of quantum mechanics.

PBR Theorem Tested on Superconducting Qubits

Scientists implemented the Pusey-Barrett-Rudolph (PBR) no-go theorem on a 156-qubit superconducting processor, investigating whether quantum states merely reflect a lack of knowledge about an underlying physical reality. By preparing qubits in specific non-orthogonal states and evolving them using carefully compiled circuits, the scientists tested the limits of explanations based solely on incomplete knowledge. The study analyzed outcome statistics from adjacent qubit pairs and five-qubit configurations, revealing a clear trend demonstrating that the probability of successfully passing the PBR test decreases as the spatial separation between qubits on the processor increases. This highlights the sensitivity of the protocol to both connectivity and coherence within Noisy Intermediate-Scale Quantum (NISQ) systems, demonstrating that maintaining quantum information across larger distances remains a significant challenge.

Researchers derived a noise-aware error tolerance model based on detailed decoherence calibrations specific to the processor, allowing them to account for imperfections inherent in real quantum hardware. Results demonstrate tension with ψ-epistemic models adhering to preparation independence, with experimental outcomes for two-qubit cases showing strong contradiction with ψ-epistemic predictions within error margins. This work provides strong evidence supporting the idea that quantum states possess an ontic reality, rather than simply reflecting our lack of knowledge.