Quantum mechanics allows measurements that surpass the fundamental sensitivity limits of classical methods. To benefit from the quantum advantage in a practical setting, the receiver should use communication channel resources optimally; this can be done employing large communication alphabets. Here we show the fundamental sensitivity potential of a quantum receiver for coherent communication with frequency shift keying. We introduce an adaptive quantum protocol for this receiver and show that its sensitivity outperforms other receivers for alphabet sizes above 4 and scales favorably, whereas quantum receivers explored to date suffer from degraded sensitivity with the alphabet size. In addition, we show that the quantum measurement advantage allows much better use of the frequency space in comparison to classical frequency keying protocols and orthogonal frequency division multiplexing.

中文翻译：

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用于大字母通信的量子接收器

量子力学可以进行超出经典方法基本灵敏度极限的测量。为了在实际环境中受益于量子优势，接收器应最佳地使用通信信道资源。这可以通过使用较大的通信字母来完成。在这里，我们展示了量子接收器用于频移键控相干通信的基本灵敏度潜力。我们为该接收器引入了一种自适应量子协议，并表明对于4以上的字母大小，其灵敏度优于其他接收器，并且缩放比例有利，而迄今为止探索的量子接收器的灵敏度随字母大小而降低。此外，