Denoising Wavelength-Multiplexed Time-Bin Correlated Photons for Quantum Networks

We present the capabilities of the quantum Talbot array illuminator (qTAI) for denoising wavelength-multiplexed time-bin correlated photons that would be employed in a quantum network. Incoherent noise, exhibiting fast amplitude and phase variations, represents a major obstacle towards the development of quantum communication technologies. This is particularly challenging when the photons have a short spectral bandwidth, such as generated by atomic ensembles or microring resonators, because it remains challenging to conceive low-loss, high-rejection filters with sub-GHz bandwidths. Using electro-optic temporal phase modulation and dispersive propagation, the qTAI implements a coherent energy redistribution scheme the coherent biphoton wavefunction is redistributed into narrow peaks. In contrast, the incoherent noise background remains virtually unaffected by these manipulations, such that the relevant biphoton signal can be discerned by the noisy background, enabling noise mitigation with ~1.5 GHz bandwidth. Here we show the improvement of the coincidence-to-accidental ratio (CAR), which is directly related to the quantum bit error rate (QBER), for various pump powers and noise injection rates. Two wavelength-multiplexed quantum channels are simultaneously denoised using a single qTAI device, which denoises the quantum signals without the need for spectral or temporal alignment beyond usual time-bin measurement approaches. Our results demonstrate that the qTAI can enable secure communications in channels that would otherwise be too noisy to allow for a quantum-secured link.