Abstract
Non-conventional receivers for phase-coherent states based on non-Gaussian measurements such as photon counting surpass the sensitivity limits of shot-noise-limited coherent receivers, the quantum noise limit (QNL). These non-Gaussian receivers can have a significant impact in future coherent communication technologies. However, random phase changes in realistic communication channels, such as optical fibers, present serious challenges for extracting the information encoded in coherent states. While there are methods for correcting random phase noise with conventional heterodyne detection, phase-tracking for non-Gaussian receivers surpassing the QNL is still an open problem. Here we demonstrate phase tracking for non-Gaussian receivers to correct for time-varying phase noise while allowing for decoding beyond the QNL. The phase-tracking method performs real-time parameter estimation and correction of phase drifts using the data from the non-Gaussian discrimination measurement, without relying on phase reference pilot fields. This method enables non-Gaussian receivers to achieve higher sensitivities and rates of information transfer than ideal coherent receivers in realistic channels with time-varying phase noise. This demonstration makes sub-QNL receivers a more robust, feasible, and practical quantum technology for classical and quantum communications.
Highlights
Optical communication with coherent states can achieve the highest rate of information transfer through lossy and noisy channels [1,2,3]
This scenario allows us to investigate phase tracking of random phase drifts in the channel and the impact of tracking bandwidth on the performance of non-Gaussian receivers
Our experimental demonstration shows that the phase-tracking method provides non-Gaussian receivers with the required robustness to overcome random phase noise encountered in realistic communication channels, and enables the receiver to perform measurements beyond the quantum noise limit (QNL) under diverse conditions with different noise strengths and bandwidths
Summary
Optical communication with coherent states can achieve the highest rate of information transfer through lossy and noisy channels [1,2,3]. Efficient coherent modulation and detection can dramatically increase the rate of information transfer beyond the reaches of intensity encodings [5,6,7]. Coherent encodings are highly susceptible to phase noise and random phase variations in real-world devices and communication channels [5,6]. To ensure the expected advantage of coherent communications over intensity modulation and direct detection, communication protocols require efficient methods for phase estimation and phase tracking to correct for random phase changes induced by the channel [5,6,7], while being compatible with existing communication technologies. Practical scenarios in low-power and quantum communications require phase tracking based only on the transmitted
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