Efficient Satellite QKD Strategy Using High‐Brightness Entangled Photon‐Pair Source with Fixed‐Intensity

Abstract A high‐brightness entangled photon‐pair (HBEPP) source is essential for long‐reach entanglement‐based quantum key distribution (QKD) such as in a satellite QKD system. An ultrabright source is a good candidate to overcome significant losses and to increase the sifted key rate, but the performance is critically limited due to the multi‐photon effect that raises the error rate of the system. To accurately estimate system performance, this study first investigates an analytical model for calculating the measurement probabilities of HBEPP distribution through an asymmetric loss channel. Based on this model, this study proposes the use of a fixed‐intensity HBEPP source for satellite QKD systems, assuming a polarization‐independent channel and threshold detectors for measurement. This study confirms that fixing the mean photon number at achieves a performance of compared to the ideal one‐way communication entanglement‐based satellite QKD protocol, which is effectively optimizing the HBEPP source brightness in accordance with system losses.