Diagram of an experimental device for a Hardy Paradox test without security holes. Image credit: Si-Ran Zhao et.al
A research team has succeeded for the first time in testing Hardy’s paradox without loopholes. The team successfully demonstrated Hardy’s nonlocality, closing both the detection efficiency gap and the locality gap.
Their results were published in Physical Examination Letters as “Editor’s Suggestion”. The team includes members of the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences (CAS) led by Prof. Pan Jianwei, Zhang Qiang and Chen Kai in collaboration with Chen Jingling of Nankai University.
The Hardy paradox, introduced by Lucien Hardy in the 1990s, provides a simplified test of local realism – the classical idea that physical properties exist independently of observation and that no signals exceed the speed of light. This paradox reveals the conflict between quantum mechanics and local realism by showing that under certain conditions where three “Hardy events” have zero probability, quantum mechanics predicts a nonzero probability for a fourth event, which contradicts local realism.
Experimental confirmation of Hardy’s paradox is challenging due to the low probability of the fourth event. To distinguish it from noise, high accuracy and efficiency of the entanglement sources is required. Previous experiments faced two main problems: the locality gap, where the choice of measurements could affect the results, and the gap in detection efficiency due to optical losses.
To close the locality gap, the researchers carefully designed a spatiotemporal experimental setup that ensured that the measurement options were spacelike and separated from both the entangled state preparations and the photon detections. This configuration eliminates any possibility that the measurement settings are influenced by the results, thus closing the locality gap.
To bridge the gap in detection efficiency, the study employed a high detection efficiency of 82.2%, which significantly mitigates the effects of optical losses. In addition, the integration of high-speed quantum random number generators for the selection of measurement settings introduced an element of true randomness, thus protecting against possible manipulation by local hidden variables.
By including undetected events and double-click events in their analysis using a refined form of the Hardy inequality, the researchers were able to effectively close the gap in detection efficiency and present a robust experimental framework that represents a significant contribution to the field of quantum physics.
Finally, the six-hour experiment showed a strong violation of Hardy’s paradox with a significance level of up to 5 standard deviations in 4.32 billion trials. A null hypothesis test confirmed that the probability of explaining the results by local realism is less than 10.-16348and provides convincing evidence for the assumption of quantum nonlocality.
This research deepens our understanding of quantum mechanics and has significant implications for the development of quantum technologies such as quantum key distribution and quantum random number certification. It represents an advance in quantum physics, provides new evidence for quantum nonlocality, and paves the way for future quantum information technologies.
Further information:
Si-Ran Zhao et al, Loophole-free test of local realism using Hardy violation, Physical Examination Letters (2024). DOI: 10.1103/PhysRevLett.133.060201. On arXiv: DOI: 10.48550/arxiv.2401.03505
Provided by the University of Science and Technology of China
Quote: Quantum nonlocality demonstrated in first loophole-free test of Hardy paradox (27 August 2024), retrieved on 27 August 2024 from https://phys.org/news/2024-08-quantum-nonlocality-loophole-free-hardy.html
This document is subject to copyright. Except for the purposes of private study or research, no part of it may be reproduced without written permission. The contents are for information purposes only.
