Abstract
Polarization encoding has been extensively used in quantum key distribution (QKD) implementations along free-space links. However, the calculation model to characterize channel transmittance and quantum bit error rate (QBER) for free-space QKD has not been systematically studied. As a result, it is often assumed that misalignment error is equal to a fixed value, which is not theoretically rigorous. In this paper, we investigate the depolarization and rotation of the signal beams resulting from spatially-dependent polarization effects of the use of curved optics in an off-axis configuration, where decoherence can be characterized by the Huygens–Fresnel principle and the cross-spectral density matrix (CSDM). The transmittance and misalignment error in a practical free-space QKD can thus be estimated using the method. Furthermore, the numerical simulations clearly show that the polarization effect caused by turbulence can be effectively mitigated when maintaining good beam coherence properties.
Highlights
Quantum key distribution (QKD) can provide an information theoretic security to share keys between two distant parties [1,2,3]
In a free-space polarization-encoded QKD, the spatially-dependent polarization effects resulting from the use of curved optics in an off-axis configuration will lead to decoherence of the quits and rotation of the polarization angle [14,15,16], which will directly
We propose a method based on based on the cross-spectral density matrix (CSDM)
Summary
Quantum key distribution (QKD) can provide an information theoretic security to share keys between two distant parties [1,2,3]. In a free-space polarization-encoded QKD, the spatially-dependent polarization effects resulting from the use of curved optics in an off-axis configuration will lead to decoherence of the quits and rotation of the polarization angle [14,15,16], which will directly. Applications,if ifone one implement a QKD over a free-space chanbetween a satellite platform andand a ground station, thethe turbulence may nel between a satellite platform a ground station, turbulence maycause causethe thebeam beam depolarization and the rotation of polarization angle, as Figure shows. It is indicated that the phase distortion caused by atmospheric turbulence eventually leads to a beam decoherence [26]
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