Efficient heralding of O-band passively spatial-multiplexed photons for noise-tolerant quantum key distribution

Abstract

When implementing O-band quantum key distribution on optical fiber transmission lines carrying C-band data traffic, noise photons that arise from spontaneous Raman scattering or insufficient filtering of the classical data channels could cause the quantum bit-error rate to exceed the security threshold. In this case, a photon heralding scheme may be used to reject the uncorrelated noise photons in order to restore the quantum bit-error rate to a low level. However, the secure key rate would suffer unless one uses a heralded photon source with sufficiently high heralding rate and heralding efficiency. In this work we demonstrate a heralded photon source that has a heralding efficiency that is as high as 74.5%. One disadvantage of a typical heralded photon source is that the long deadtime of the heralding detector results in a significant drop in the heralding rate. To counter this problem, we propose a passively spatial-multiplexed configuration at the heralding arm. Using two heralding detectors in this configuration, we obtain an increase in the heralding rate by 37% and a corresponding increase in the heralded photon detection rate by 16%. We transmitted the O-band photons over 10 km of noisy optical fiber to observe the relation between quantum bit-error rate and noise-degraded second-order correlation function of the transmitted photons. The effects of afterpulsing when we shorten the deadtime of the heralding detectors are also observed and discussed.

Broadband fiber-based entangled photon-pair source at telecom O-band

“…A biphoton source centered near the zero-dispersion wavelength (around 1310 nm) of the telecom silica fiber may resolve this problem and improve the precision of timing [8]. Various entangled photon sources at telecom O-band (1260 -1360 nm) with a biphoton emission bandwidth up to 70 nm have been developed [9][10][11][12][13][14][15][16]. However, this bandwidth is still lacking.…”