The satellite time service technology is limited by the measurement accuracy of the classical radio signal, and the time service accuracy can only reach the ns level.In this paper, a satellite time service scheme based on microwave - optical wave -entangled signals is proposed.The advantages of long -distance transmission of microwave signals and single - photon detection of optical wave signals are effectively combined using a cavity electro -opto -mechanical converter.The phase difference is calculated using a phase -conjugating processor to obtain accurate time -difference information.Through theoretical analysis and simulations, it is demonstrated that even if the quantum signal is in low entanglement, the proposed scheme can improve the satellite time service accuracy to the ps level.
The satellite time service technology is limited by the measurement accuracy of the classical radio signal, and the time service accuracy can only reach the ns level.In this paper, a satellite time service scheme based on microwave - optical wave -entangled signals is proposed.The advantages of long -distance transmission of microwave signals and single - photon detection of optical wave signals are effectively combined using a cavity electro -opto -mechanical converter.The phase difference is calculated using a phase -conjugating processor to obtain accurate time -difference information.Through theoretical analysis and simulations, it is demonstrated that even if the quantum signal is in low entanglement, the proposed scheme can improve the satellite time service accuracy to the ps level.
Due to the limitation of the measurement accuracy of classical radio signals, the time comparison accuracy can only reach ns level. In this paper, a time comparison scheme of BeiDou system based on microwave-optical entangled signal is proposed, which effectively combines the long-distance transmission advantage of microwave signal with the single photon detection advantage of optical signal by electro-opto-mechanical converter, and the phase difference is solved by a phase conjugate processor ,so as to calculate the accurate time difference information. Through theoretical analysis and simulation, it is proved that even if the quantum signal is under the condition of low entanglement degree, the proposed scheme can improve the time comparison accuracy to the ps level.
Satellite quantum communications have rapidly evolved in the past few years, culminating in the proposal, development, and deployment of satellite missions dedicated to quantum key distribution and the realization of fundamental tests of quantum mechanics in space. However, in comparison with the more mature technology based on fiber optics, several challenges are still open, such as the capability of detecting, with high temporal accuracy, single photons coming from orbiting terminals. Satellite laser ranging, commonly used to estimate satellite distance, could also be exploited to overcome this challenge. For example, high repetition rates and a low background noise can be obtained by determining the time-of-flight of faint laser pulses that are retro-reflected by geodynamics satellites and then detected on Earth at the single-photon level. Here we report an experiment with regard to achieving a temporal accuracy of approximately 230 ps in the detection of an optical signal of few photons per pulse reflected by satellites in medium Earth orbit, at a distance exceeding 7500 km, by using commercially available detectors. Lastly, the performance of the Matera Laser Ranging Observatory is evaluated in terms of the detection rate and the signal-to-noise ratio for satellite quantum communications.
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 single-photon 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.
Microwaves exhibit superior performance in free-space transmission compared to optical waves, primarily due to their ability to penetrate fog and experience lower losses in the Earth's atmosphere. Based on microwave-optical entanglement prepared by nano-cavity electro-opto-mechanic converters, we propose a scheme of a quantum positioning system using the distance-based positioning method. Principles of microwave-optical entanglement preparation and our QPS scheme are introduced in detail. The entanglement feature, system stability and positioning feature of the scheme are analyzed after simulations. Furthermore, we delve into the impact of key parameters, such as transmissivity and photon conversion efficiency, on positioning. Notably, the entanglement degrees for both microwave-optic entanglement at the transmitter and optic-optic entanglement at the receiver surpass one, affirming the efficiency of the scheme in preparing and maintaining entanglement. When transmissivity in beam-splitter models of both ground stations equals 0.5, our scheme achieves a minimal positioning error of 6.4×10-7m2 under ideal conditions. Additionally, we map out traces of a plane through continuous positioning using our scheme. These results demonstrate the theoretical efficiency and robustness of our proposed approach.
A quantum ranging scheme based on dual-path entangled microwaves and coherent detection is proposed to avoid the difficulties of low security, limited precision in traditional radio navigation ranging schemes, being sensitive to multipath effect and the poor performance of existing quantum ranging schemes in current navigation systems. Based on the characteristic that orthogonal quadrature of dual-path entangled microwaves has the largest cross-correlation when the two signals are synchronized, coherent detection is used to get the reference electromagnetic information and calculate the time delay. Based on the principle of pseudo code acquisition and tracking of satellite navigation receiver, a synchronization scheme of time delay is designed, which can acquire the accurate distance ranging. Simulated analysis is implemented in precision and anti- interference, which provide theoretical support for application of dual-path entangled microwaves and a new type of quantum navigation position technology.
Abstract Frequency conversion between microwave and optical photons is a key enabling technology to create links between superconducting quantum processors and to realize distributed quantum networks. We propose a microwave-optical transduction platform based on long-coherence time superconducting radio-frequency (SRF) cavities coupled to electro-optic optical cavities to mitigate the loss mechanisms that limit the attainment of high conversion efficiency. We optimize the microwave-optical field overlap and optical coupling losses in the design while achieving long microwave and optical photon lifetime at milli-Kelvin temperatures. This represents a significant enhancement of the transduction efficiency up to 50% under incoming pump power of 140 μW, which allows the conversion of few-photon quantum signals. Furthermore, this scheme exhibits high resolution for optically reading out the dispersive shift induced by a superconducting transmon qubit coupled to the SRF cavity. We also show that low microwave losses enhance the fidelity of heralded entanglement generation between two remote quantum systems. Finally, high precision in quantum sensing can be reached below the standard quantum limit.