Fig. 2: Schematics of quantum state generation and processing for 4- and 8-level entangled qudits.
From: Quantum key distribution implemented with d-level time-bin entangled photons
a Simplified experimental setup for the generation of picosecond-spaced high-dimensional time-bin entangled photonic qudits. b Operation principle for 4-level quantum state processing using the OIC and external phase modulation (see “Methods” and Supplementary Note 1). c Simplified scheme for 8-level quantum interference measurements, where the phase of each photon time bin was prepared by applying a phase modulation to the pump before photon generation. For clarity, the position of the phase modulator (PM*) is indicated in the setup. We applied temporal gating to separate the central interference modes and hence account for the fact that the time bin spacing (i.e., 32 ps and 64 ps) approaches the jitter time (i.e., ~52 ps) of the superconducting nanowire single-photon detectors. OIC: on-chip interferometer cascade, SW: spiral waveguide, NF: notch filter, FBG: fiber Bragg grating, PM: phase modulator, IM: intensity modulator, DEMUX: demultiplexer. Adapted with permission from ref. 34 © Optica Publishing Group.
