Scientists have shown through experiments that there is no universal standard possible for measuring and quantifying nonlocal quantum correlations. Quantum nonlocality describes the unique relationship between distant physical objects that does not allow for faster-than-light communication. This new research broadens the potential applications of quantum nonlocal correlations. They are already used in secure communications, random number generation, and cryptographic key generation.
Since its inception, quantum nonlocality has attracted attention in the natural sciences because of its broad appeal, influencing recent advances in machine-free technologies. Its story began in 1964 when Northern Irish physicist John Stewart Bell presented a theorem that changed our view of the quantum world. Bell showed that while 'local realism' is true in classical physics, it does not apply at the quantum level. 'Local realism' is the view that objects have fixed properties independent of observation and are only affected by their surroundings. Quantum systems with multiple, distant parts show correlations that cannot be explained by local realism.
Bell's theorem was later confirmed through experiments. This confirmation established the nonlocal nature of the quantum world and was recognised with the 2022 Nobel Prize in Physics. Since then, quantum nonlocality has become a crucial resource for secure communication, random number authentication and cryptographic key generation. This has made it important to understand how to measure and compare these quantum correlations. Scientists have been searching for a complete framework to compare the strength of such nonlocal resources. In a recent study published in Physical Review Letters, Dr Manik Banik from the SN Bose National Centre for Basic Sciences, an autonomous institute of the Department of Science and Technology, along with colleagues from the Indian Statistical Institute Kolkata, ABN Seal College Cooch Behar and the University of Hong Kong showed that a universal standard for measuring quantum nonlocality is impossible.
Their research shows that the nature of nonlocality varies depending on the type of correlation. It consists of infinite unique points on the correlation boundary. This means that there is no single, ubiquitous topological resource in the world of nonlocality. Instead, each nonlocal resource is distinct, capable of performing specific functions that others cannot. This discovery further enhances our understanding of quantum mechanics, highlighting the complexity and uniqueness of quantum nonlocality as a valuable and diverse resource.