Observing High-dimensional Bell Inequality Violations using Multi-Outcome Spectral Measurements
Abstract
Violation of Bell inequalities is an essential requirement for many quantum information and communication protocols. In high-dimensional systems, Bell inequality tests face the challenge of implementing genuinely multi-outcome measurements, since the emulation of these with separate dichotomic projections opens a binarisation loophole that local hidden variable theories can exploit. Here we show that the joint spectral intensity of a two-photon entangled state contains access to the necessary multi-outcome measurements to overcome this obstacle and certify and violate a Bell inequality for high-dimensional states. This result is contrary to the belief that the joint spectral intensity is a phase-insensitive quantity and does not have sufficient information to certify entanglement or Bell-nonlocality. Using this approach, we violate the CGLMP Bell inequality up to dimension d = 8, all with negligible p-values, and for the first time close the binarisation loophole in high-dimensional Bell experiments. Guaranteeing Bell-nonlocal correlations using frequency-only measurements removes the technological hurdle of measurements in the temporal domain, thus greatly simplifying any practical implementation of future high-dimensional quantum information protocols.
Cite
@article{arxiv.2506.20796,
title = {Observing High-dimensional Bell Inequality Violations using Multi-Outcome Spectral Measurements},
author = {Kiki Dekkers and Laura Serino and Nicola DAlessandro and Abhinandan Bhattacharjee and Benjamin Brecht and Armin Tavakoli and Christine Silberhorn and Jonathan Leach},
journal= {arXiv preprint arXiv:2506.20796},
year = {2025}
}