  The performances of optical fibre-based quantum information systems are
limited by the intrinsic properties of silica glass materials, e.g. high
latency, Rayleigh-scattering loss wavelength scaling law, and cross-coupling
induced modal impurity. Hollow-core optical fibre (HCF) promises to unify
air-borne light propagation and non-line-of-sight transmission, thus holding
great potentials for versatile photonics-based quantum infor-mation
applications. The early version of HCF based on photonic-bandgap guidance has
not proven itself as a reliable quantum channel because of the poor modal
purity in both spatial and polarization domains, as well as significant
difficulty in fabrication when the wavelength shifts to the visible region. In
this work, based on the polarization degree of freedom, we first, to the best
of our knowledge, demonstrate high-fidelity (~0.98) single-photon transmission
and distribution of entangled photons over a conjoined-tube hollow-core fibre
(CTF) by using commercial silicon single-photon avalanche photodiodes. Our CTF
realized the combined merits of low loss, high spatial mode purity, low
polarization degradation, and low chromatic dispersion. We also demonstrate
single-photon low latency (~99.96% speed of light in vacuum) transmission, thus
paving the way for extensive uses of HCF links in versatile polarization-based
quantum information processing.
