Harnessing Hybrid Frequency-Entangled Qudits through Quantum Interference

Abstract: High-dimensional (HD) quantum entanglement expands the Hilbert space, offering a robust framework for quantum information processing with enhanced capacity and error resilience. In this work, we present a novel HD frequency-domain entangled state, the hybrid frequency-entangled qudit (HFEQ), generated via Hong-Ou-Mandel (HOM) interference, exhibiting both discrete-variable (DV) and continuous-variable (CV) characteristics in the frequency domain. By tuning HOM interference, we generate and control HFEQs with dimensions $D=5,7,9,11, confirming their DV nature. Franson interferometry confirms the global frequency correlations with visibility exceeding 98% and verifies the CV entanglement within individual frequency modes with visibility greater than 95%. Our findings provide deeper insight into the physical nature of frequency-entangled qudits generated by quantum interference and introduce a novel resource for HD time-frequency quantum information processing.