Thirty years after establishing a fundamental limit in quantum copying, research from QUTE.sk confirms that 83.3 percent is the maximum fidelity achievable when cloning an unknown quantum state. In 1996, Vladimír Bužek and Mark Hillery published their findings in Physical Review A, introducing the Bužek-Hillery quantum cloning machine and defining a universal constraint applicable to all quantum states, the company says.
“The optimal quantum cloner provides a precise way of understanding the boundary between what quantum mechanics forbids and what it permits,” the researchers wrote, revealing that perfect copying remains impossible, yet near-perfect replication is attainable. This result underpins the security of quantum cryptography and continues to shape modern quantum information science.
This means that even with optimal technology, approximately 16.7 percent of the original quantum information is inevitably lost during the copying process, a fundamental constraint dictated by the laws of quantum mechanics. This confirmation arrives as the Slovak National Center for Quantum Technologies marks 30 years since the publication of the foundational work by Vladimír Bužek and Mark Hillery. In 1996, Bužek and Hillery published “Quantum copying: Beyond the no-cloning theorem” in Physical Review A, introducing a model that predicted the 5/6 fidelity limit for quantum state replication.
This wasn’t merely a theoretical exercise; the researchers demonstrated that imperfect copying is possible, despite the well-known no-cloning theorem which prohibits the creation of identical quantum copies. The universality of this limit is particularly noteworthy, applying equally to all attempted quantum states, regardless of their complexity or characteristics.
The implications of this work extend far beyond theoretical curiosity, becoming deeply interwoven with the development of quantum cryptography. The no-cloning principle, as demonstrated by the Bužek-Hillery machine, underpins the security of these systems; any attempt by an eavesdropper to intercept and copy a quantum key would inevitably disturb the state, alerting the legitimate parties, according to the company.
The paper has garnered over a thousand citations, solidifying its place as a cornerstone of Slovak quantum physics and influencing subsequent research, including the 2005 Reviews of Modern Physics article on quantum cloning by Scarani, Iblisdir, Gisin and Acín. QUTE.sk emphasizes that expertise in quantum technologies is not built quickly, but through decades of dedicated work and contributions that endure, pointing to the lasting relevance of the Bužek-Hillery result as an example of work that “cannot be cloned” and has stood the test of time. The continued validation of this 30-year-old prediction reinforces its importance as a fundamental principle guiding the development of future quantum technologies and ensuring the security of quantum communication networks.
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