Surpassing the classical limit of the microwave photonic frequency fading effect by quantum microwave photonics

With energy-time entangled biphoton sources as the optical carrier and time-correlated single-photon detection for high-speed radio frequency(RF)signal recovery,the method of quantum microwave photonics(QMWP)has presented the unprecedented potential of nonlocal RF signal encoding and efficient RF signal distilling from the dispersion interference associated with ultrashort pulse carriers.In this paper,its capability in microwave signal processing and prospective superiority are further demonstrated.Both QMWP RF phase shifting and transversal filtering functionality,which are the fundamental building blocks of microwave signal processing,are realized.Besides good immunity to the dispersion-induced frequency fading effect associated with the broadband carrier in classical MWP,a native two-dimensional parallel microwave signal processor is provided.These results well demonstrate the superiority of QMWP over classical MWP and open the door to new application fields of MWP involving encrypted processing.

Single-photon microwave photonics

With the rapid development of microwave photonics technology, high-speed processing and ultra-weak signal detection capability have become the main bottlenecks in many applications. Thanks to the ultraweak signal detection capability and the extremely low timing jitter properties of single-photon detectors, the combination of single-photon detection and classical microwave photonics technology may provide a solution to break the above bottlenecks. In this paper, we first report a novel concept of singlephoton microwave photonics(SP-MWP), a SP-MWP signal processing system with phase shifting and frequency filtering functionalities is demonstrated based on a superconducting nanowire single photon detector(SNSPD) and a successive time-correlated single photon counting(TCSPC) module.Experimental results show that an ultrahigh optical sensitivity down to-100 d Bm has been achieved,and the signal processing bandwidth is only limited by the timing jitter of single-photon detectors. In the meantime, the proposed system demonstrates an ultrahigh anti-interference capability, only the signal which is phase locked by the trigger signal in TCSPC can be extracted from the detected signals combining with noise and strong interference. The proposed SP-MWP concept paves a way to a novel interdisciplinary field of microwave photonics and quantum mechanism, named by quantum microwave photonics.

Quantum microwave photonics in radio-over-fiber systems

As the main branch of microwave photonics,radio-over-fiber technology provides high bandwidth,low-loss,and long-distance propagation capability,facilitating wide applications ranging from telecommunication to wireless networks.With ultrashort pulses as the optical carrier,a large capacity is further endowed.However,the wide bandwidth of ultrashort pulses results in the severe vulnerability of high-frequency radio frequency(RF)signals to fiber dispersion.With a time-energy entangled biphoton source as the optical carrier combined with the singlephoton detection technique,a quantum microwave photonics method in radio-over-fiber systems is proposed and demonstrated experimentally.The results show that it not only realizes unprecedented nonlocal RF signal modulation with strong resistance to the dispersion but also provides an alternative mechanism to distill the RF signal out from the dispersion effectively.Furthermore,the spurious-free dynamic ranges of the nonlocally modulated and distilled RF signals have been significantly improved.With the ultra-weak detection and the high-speed processing advantages endowed by the low-timing-jitter single-photon detection,the quantum microwave photonics method opens new possibilities in modern communication and networks.