自由空间大气信道连续变量量子通信中光束漂移引起的透射率起伏的稳定
Stabilization of transmittance fluctuations caused by beam wandering in continuous-variable quantum communication over free-space atmospheric channels
摘要：
湍流大气信道中的透射率起伏导致正交多余噪声，这限制了连续变量量子通信的适用性。这种波动通常是由光束在接收孔径周围徘徊引起的。我们研究了通过扩展光束来稳定涨落的可能性，并在连续变量纠缠共享和量子密钥分发方面测试了这种信道稳定性。我们进行一个真正的自由空间大气信道的透射率测量不同的光束宽度，并表明，光束扩展减少了信道透射率的波动的成本增加的整体损失。我们还从理论上研究了在不同光束宽度的湍流大气信道中共享纠缠态或建立安全的量子密钥分发的可能性。我们展示了光束扩展对连续变量量子通信的信道稳定的积极影响，以及优化方法以最大化密钥速率或共享纠缠量的必要性。由于是自主的并且不需要基于光束漂移的表征对源和检测器进行自适应控制，光束扩展的方法还可以与旨在稳定波动的自由空间大气信道的其他方法相结合。
英文摘要：
Transmittance fluctuations in turbulent atmospheric channels result in quadrature excess noise which limits applicability of continuous-variable quantum communication. Such fluctuations are commonly caused by beam wandering around the receiving aperture. We study the possibility to stabilize the fluctuations by expanding the beam, and test this channel stabilization in regard of continuous-variable entanglement sharing and quantum key distribution. We perform transmittance measurements of a real free-space atmospheric channel for different beam widths and show that the beam expansion reduces the fluctuations of the channel transmittance by the cost of an increased overall loss. We also theoretically study the possibility to share an entangled state or to establish secure quantum key distribution over the turbulent atmospheric channels with varying beam widths. We show the positive effect of channel stabilization by beam expansion on continuous-variable quantum communication as well as the necessity to optimize the method in order to maximize the secret key rate or the amount of shared entanglement. Being autonomous and not requiring adaptive control of the source and detectors based on characterization of beam wandering, the method of beam expansion can be also combined with other methods aiming at stabilizing the fluctuating free-space atmospheric channels.
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