Fig. 4: Measurement of SpRS noise.

a Optical spectra with different notches. b Measured photon counts over time when the quantum receiver is at different notches (one active at a time). c Raman photon counts as a function of the quantum channel’s wavelength. The solid line is the theory. d Optical spectra with different launch powers to the fiber core. The quantum channel (Q) is at the longest wavelength in this and subsequent panels. e Raman photon counts versus launch power. f Measured photon counts over time from cores 1–3 and all cores. g Contributions of dark counts, cores 1–3, and all cores. h Measured photon counts over time at different fiber lengths. i Raman photon counts as a function of the fiber length. The solid line is the theory