Fiber Source of Biphotons with Ultrabroad Frequency Tuneability

Photon pairs (biphotons) are ubiquitous in quantum technologies. In particular, in quantum imaging and spectroscopy they enable measurements in hard-to-access spectral ranges [1] and increased sensitivity [2] . Among different sources of biphotons, four-wave mixing (FWM) in optical fibers is most efficient due to the large nonlinear interaction lengths and easy integrability into optical networks. However, fiber sources are usually not tuneable except by tuning the pump wavelength. Hollow-core photonic crystals fibers (PCF) filled by noble gas solve this problem: their dispersion landscape can be tailored by simply changing the gas pressure [3] , [4] . Additionally, they are free from Raman scattering and have a higher damage threshold than solid-core fibers [4] .