There is an increasing and demanding interest in the realization of secure communication schemes. Here, we conceive and realize an approach for a message-encoding scheme between two parties, Alice and Bob, by exploiting the infinite number of polarization states of unpolarized thermal light on the Poincaré sphere together with their correlation properties to camouflage and recover a message, thus realizing ghost polarization communication. At first, we investigate the second-order correlation coefficient $g^{(2)}(\tau )$ of classical unpolarized broadband amplified-spontaneous-emission light emitted by an erbium-doped fiber amplifier at 1550 nm by manipulating its instantaneous polarization state utilizing various polarization optics in the beam paths of a Hanbury-Brown and Twiss like ghost polarimetry setup using ultra-fast two-photon absorption in a photomultiplier tube. The observed polarization state modifications are in excellent agreement with our developed model based on the Stokes vector dynamics and a Glauber protocol for $g^{(2)}(\tau )$. On the basis of these results we then proceed towards the realization of a message-encoding scheme. By changing the instantaneous polarization state using a half-wave plate, Alice encodes and subsequently transmits a message. The camouflaged message can be recovered uniquely by Bob measuring the second-order correlations of the modified instantaneous polarization state with his reference beam. By using the agreed keypad of the communication scheme, he is able to retrieve the bit values of the encoded message. Finally, we address real-world implementation of this first proof-of-principle demonstration and discuss its security issues. This scheme demonstrates a method of establishing a secure communication link between two parties directly on the physical layer based on polarization correlations of classical light. It is expected that by the realization of this correlated photon modality not only avenues for ghost modalities, in general, are opened but also insight into polarization, even more than 175 years after Stokes will be achieved.

中文翻译：

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鬼极化通信

对实现安全通信方案的兴趣与日俱增。在这里，我们通过利用庞加莱球上无限数量的非偏振热光的偏振态及其相关特性来伪装和恢复消息，从而构想并实现了两方Alice和Bob之间的消息编码方案，从而实现了鬼极化通信。首先，我们研究二阶相关系数$G^{（2）}（\tau ）$掺Han光纤放大器在1550 nm处通过利用Hanbury-Brown和Twiss的光束路径中的各种偏振光学器件操纵其瞬时偏振态而进行的经典非偏振宽带放大自发光的成像，如使用超快的鬼像偏振仪光电倍增管中的两个光子吸收。观察到的偏振态变化与我们基于Stokes矢量动力学和Glauber协议开发的模型非常吻合$G^{（2）}（\tau ）$。基于这些结果，我们接着进行消息编码方案的实现。通过使用半波片更改瞬时极化状态，Alice编码并随后发送消息。通过Bob测量修改后的瞬时偏振态与其参考光束的二阶相关性，可以唯一地恢复被伪装的消息。通过使用通信方案中约定的小键盘，他可以检索已编码消息的位值。最后，我们讨论了第一个原理证明演示的实际实现，并讨论了其安全性问题。该方案演示了一种基于经典光的偏振相关性在物理层上直接在两方之间建立安全通信链路的方法。