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Coherence and Dimensionality Witnesses for Fractional OAM Modes
A. L. S. Santos Junior, I. Prego, M. Gil de Oliveira, A. C. Barbosa, B. P. da Silva, D. J. Brod, E. F. Galvão, A. Z. Khoury·September 16, 2025
Quantum Physicsphysics.optics
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Abstract
We characterize sets of fractional orbital angular momentum (OAM) modes of a light beam using unitary-invariant properties encoded by two-mode overlaps. Using basis-independent coherence and dimension witnesses, we experimentally certify, on a triple of fractional modes, both the presence of coherence and that the states necessarily span a space of dimension 3. We propose and implement a practical, fast experimental method to extract two-mode overlaps requiring only a single intensity image per interference pair. These results lay the groundwork for using fractional OAM states in high-dimensional quantum information protocols.