通过下行链路信道与卫星进行增强的上行链路量子通信
Enhanced Uplink Quantum Communication with Satellites via Downlink Channels
摘要：
在发展全球量子互联网的过程中，与低地球轨道卫星的量子通信将发挥关键作用。这种通信将需要是双向的：不仅在卫星对地面（下行链路）信道中有效，而且在地面对卫星信道（上行链路）中有效。考虑到后者信道上的损耗相对于前者要大得多，应该探索可以利用优越的下行链路来增强上行链路中的量子通信的技术。在这项工作中，我们就是这样做的-探索如何连续变量纠缠的双模压缩真空（TMSV）状态的形式可以用来显着提高保真度的地面到卫星的量子态传输相对于直接上行链路传输。更具体地说，通过详细的相位屏模拟光束演化通过湍流大气中的下行链路和上行链路信道，我们演示了如何TMSV隐形传态信道创建的卫星可以用来显着提高保真度的上行链路相干状态传输相对于直接传输。然后，我们将展示如何，反过来，导致上行链路传输更高的字母表的相干态。此外，我们展示了如何在地面站的TMSV状态的接收到的组件上的非高斯操作可以导致进一步增强。由于TMSV状态可以很容易地在卫星平台上原位产生，并为大多数量子态形成可靠的隐形传态信道，我们的工作表明，未来的卫星形成新兴的量子互联网的一部分，应设计通过TMSV隐形传态的上行链路通信。
英文摘要：
In developing the global Quantum Internet, quantum communication with low-Earth-orbit satellites will play a pivotal role. Such communication will need to be two way: effective not only in the satellite-to-ground (downlink) channel but also in the ground-to-satellite channel (uplink). Given that losses on this latter channel are significantly larger relative to the former, techniques that can exploit the superior downlink to enhance quantum communication in the uplink should be explored. In this work we do just that - exploring how continuous variable entanglement in the form of two-mode squeezed vacuum (TMSV) states can be used to significantly enhance the fidelity of ground-to-satellite quantum-state transfer relative to direct uplink-transfer. More specifically, through detailed phase-screen simulations of beam evolution through turbulent atmospheres in both the downlink and uplink channels, we demonstrate how a TMSV teleportation channel created by the satellite can be used to dramatically improve the fidelity of uplink coherent-state transfer relative to direct transfer. We then show how this, in turn, leads to the uplink-transmission of a higher alphabet of coherent states. Additionally, we show how non-Gaussian operations acting on the received component of the TMSV state at the ground station can lead to even further enhancement. Since TMSV states can be readily produced in situ on a satellite platform and form a reliable teleportation channel for most quantum states, our work suggests future satellites forming part of the emerging Quantum Internet should be designed with uplink-communication via TMSV teleportation in mind.
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