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Optics and Precision Engineering

ATP technology for 100-kilometer quantum entanglement distribution experiment

亓波 Qi Bo, 陈洪斌 Chen Hongbin, 任戈 Ren Ge, 黄永梅 Huang Yongmei, 丁科 Ding Ke, 马佳光 Ma Jia-guang

Published Jan 1, 2013• 2 citations
Publisher

Abstract

Acquiring,tracking and pointing(ATP) technique in a 100 km quantum entanglement distribution experiment was introduced in detail.By taking a 700 mm telescope at Alice receiving terminal as an example,the technological specification,light path layout,and tracking accuracy of the ATP system were analyzed.In order to reduce the angle-of-arrival fluctuations of quantum information transmission beams and beacon beams caused by air turbulence,a cascade acquisition and tracking system with coarse tracking,fine tracking and a ultra-fine loop was designed and a dual fast-steering mirror tracking algorithm was proposed.On the basis of a higher frame frequency CMOS detector and a piezoelectric fast-steering mirror,the ultra-fine tracking circuit was developed.Experiments show that these methods solve the contradiction between tracking dynamic range and tracking accuracy,promote the performance of the detector and improve band width and tracking accuracy.The system was used in a ground 100 km quantum entanglement distribution experiment and the results indicate that the tracking error of the system is 4 μrad for a 70 Hz bandwidth.

DOI
10.3788/ope.20132106.1628

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Acquiring,tracking and pointing(ATP) technique in a 100 km quantum entanglement distribution experiment was introduced in detail.By taking a 700 mm telescope at Alice receiving terminal as an example,the technological specification,light path layout,and tracking accuracy of the ATP system were analyzed.In order to reduce the angle-of-arrival fluctuations of quantum information transmission beams and beacon beams caused by air turbulence,a cascade acquisition and tracking system with coarse tracking,fine tracking and a ultra-fine loop was designed and a dual fast-steering mirror tracking algorithm was proposed.On the basis of a higher frame frequency CMOS detector and a piezoelectric fast-steering mirror,the ultra-fine tracking circuit was developed.Experiments show that these methods solve the contradiction between tracking dynamic range and tracking accuracy,promote the performance of the detector and improve band width and tracking accuracy.The system was used in a ground 100 km quantum entanglement distribution experiment and the results indicate that the tracking error of the system is 4 μrad for a 70 Hz bandwidth.
Quantum entanglement is the main resource to endow the field of quantum information processing with powers that exceed those of classical communication and computation. Due to low absorption and negligible nonbirefringent character in atmosphere, optical free space therefore serves as the most promising channel for large-scale quantum communication by use of satellites and ground stations. The acquisition, tracking and pointing (ATP) system is one of the most important parts of quantum experiment system, and it controls a transmitting and receiving laser beam within a few micro radians jitter because of using an extremely narrow beam divergence of several micro radians. This paper introduces the cascade ATP systems for 100km quantum entanglement distribution experiment among Charlie, Bob and Alice station. The specification and optical diagram of each ATP system are presented. The ATP system of Alice station is described in detail，it has coarse, fine and ultra-fine loop. In the 100km quantum entanglement distribution experiment, a tracking error of 4μrad is achieved for 70Hz bandwidth. The ATP strategy in this experiment can be used in the prospective satellite-to-ground quantum distribution.
A satellite dedicated for quantum science experiments, has been developed and successfully launched from Jiuquan, China, on August 16, 2016. Two new optical ground stations (OGSs) were built to cooperate with the satellite to complete satellite-ground quantum experiments. OGS corrected its pointing direction by satellite trajectory error to coarse tracking system and uplink beacon sight, therefore fine tracking CCD and uplink beacon optical axis alignment accuracy was to ensure that beacon could cover the quantum satellite in all time when it passed the OGSs. Unfortunately, when we tested specifications of the OGSs, due to the coarse tracking optical system was commercial telescopes, the change of position of the target in the coarse CCD was up to 600μrad along with the change of elevation angle. In this paper, a method of reduce alignment error between beacon beam and fine tracking CCD is proposed. Firstly, OGS fitted the curve of target positions in coarse CCD along with the change of elevation angle. Secondly, OGS fitted the curve of hexapod secondary mirror positions along with the change of elevation angle. Thirdly, when tracking satellite, the fine tracking error unloaded on the real-time zero point position of coarse CCD which computed by the firstly calibration data. Simultaneously the positions of the hexapod secondary mirror were adjusted by the secondly calibration data. Finally the experiment result is proposed. Results show that the alignment error is less than 50μrad.
Satellite based quantum key distribution (QKD) enables the delivery of keys for quantum secure communications over long distances. Maturity of the technology as well as industrial interest are ever increasing. Same is true for satellite free-space optical communications (FSOC). In order to enable a robust channel for transmission it is indispensable to account for static and dynamically changing misalignments between the transmitter and receiver pair. This work will focus on the transmitter terminal (Alice) and the design and verification process of the active beam steering system. The novelty is a recently developed variable reluctance fine steering mirror (FSM) including eddy current sensors (ECS) to measure its tip and tilt. A cascaded architecture was chosen in order to combine the optical stabilization objective with the dynamics of the mirror platform. The inner control loop makes use of an observer model whose estimated output is fed into a state controller allowing for an increased responsiveness. While high gains increase the closed loop bandwidth the eigenfrequency of the system introduces a pole to the plant which has to be avoided by the controller output. A digital notch filter was introduced to reject the excitation of the critical frequency band which gets obsolete in a system with high frequency sampling capabilities. The outer loop is engaged when a valid optical signal is received and a transition from a closed loop pointing to a closed loop tracking mode is performed. A proportional-integral (PI) controller keeps the received beam at the 4-quadrant-diode (4QD) whose center is used as the main reference through prior calibration with the transmit beam launching on the same path. The presented cascaded control scheme allows improvements in system performance and reliability.
The quantum positioning system (QPS) takes advantage of the entanglement property of the quantum system itself, and it is possible to breakthrough the limitation of the positioning accuracy due to signal bandwidth and power limitation in classical radio-based global positioning system (GPS), and improve the positioning performance. In this paper, a comprehensive survey of the research status of QPS and its several key components are presented, including the quantum entanglement states preparation, the quantum satellite technique, the optical signal acquisition, tracking and pointing (ATP) system, and the quantum positioning and clock synchronization technique. We also discuss the current challenges and future research directions at the end of the paper.