Measurement of ultrashort bi-photon correlation times with an integrated two-colour broadband SU(1,1)-interferometer

The bi-photon correlation time, a measure for the conditional uncertainty in the temporal arrival of two photons from a photon pair source, is a key performance identifier for many quantum spectroscopy applications, with shorter correlation times typically yielding better performance. Furthermore, it provides fundamental insight into the effects of dispersion on the bi-photon state. Here, we retrieve ultrashort bi-photon correlation times of around $100\mathrm{f}\mathrm{s}$ by measuring simultaneously spectral and temporal interferograms at the output of an SU(1,1) interferometer based on an integrated broadband parametric down-conversion source in a ${\mathrm{T}\mathrm{i}:\mathrm{L}\mathrm{i}\mathrm{N}\mathrm{b}\mathrm{O}}_3$ waveguide