Noise impact of classical headers on the quantum payload in quantum wrapper networking

The fundamental properties of quantum mechanics, such as the no-cloning theorem, make management and control of quantum networks challenging. Quantum wrapper networking (QWN) offers a solution to this problem by wrapping quantum payloads with classical bits (as headers and/or tails) that can be used to assist with networking, performance monitoring, and probing the properties of the fiber interconnection. Since the classical header and quantum payload travel in the same fiber, one should carefully design the system to mitigate potentially deleterious effects such as noise and cross-talk. In this paper, we identify and characterize the noise induced by the classical headers by in-fiber scattering processes. We study the noise by using a tunable continuous-wave laser to emulate O-band (∼1310 nm) classical headers, which are time- and wavelength-multiplexed with O-band quantum signals. The noise is characterized as a function of the headers’ power, classical-quantum wavelength detuning, and optical fiber length. We demonstrate that the dominant noise contribution originates from spontaneous Raman scattering for wavelength detunings that are larger than 3 nm. We also observe that some noise photons can bleed into the quantum payload due to Rayleigh scattering of backward Raman scattered photons. We further investigate system level impacts of the noise created by classical headers that are produced by employing a small form-factor pluggable transceiver. We demonstrate that the associated noise level has negligible impact on quantum payloads for a 47.8 km deployed fiber link, the longest length used in QWN experiments to date, achieving a coincidences-to-accidentals ratio of 56 and a two-photon interference visibility of 88.8%.