Being a core pillar of modern physics, quantum physics, roaring through its emerging, developing, and maturing stage during the very last century, has influenced profoundly, and is continuously reshaping the landscape of human life. Achievements of quantum physics includes, if not mentioning countless others, the invention of laser, semiconductor, and atomic clock. Quantum information technology (QIT), combination of quantum physics and information technology, is an emerging IT field maintaining restless rapid progress in the last two decades. Major QIT subjects include quantum sensing, quantum communication, quantum computation, etc. Thanks to its quantum physics characteristics, QIT enables dramatic improvement in almost every perspective of information technology, including sensing, acquiring, processing, and securing. Apart from contributions to fundamental research, substantial achievements in recent years demonstrate QIT’s unlimited potential in advanced technology R&D. The western world has shown great interest in QIT: US Department of Defense (DoD) has listed QIT among six “disruptive basic research areas” in an annual report by its assistant secretary; UK government has released its “National strategy for quantum technologies”; and EU has published “Quantum manifesto” calling for a “flagship-scale initiative in quantum technology” within its “Horizon 2020 research and innovation framework programme”. Under enormous investments, the rapid developing QIT has become a vital topic for future information science advancement. QIT Team is leaded by Prof. Hong Guo (Department of Electronics, Peking University, awardee of National Science Funding for Distinguished Young Scholars of China), the QIT team has four professors (two awardees of National Science Funding for Distinguished Young Scholars of China, two Yangtze River Scholars), and four associate professors, at the same time enrolling 26 Ph.D. candidates (25 graduated), and 19 M.Sc. /M. Eng. candidates (28 graduated). Responding the highly demanding requirements of national interest, the QIT team has been engaged in various fields, including quantum magnetic detection, quantum frequency standard, quantum time and frequency transfer, quantum cryptography, quantum optical filtering, and quantum imaging, after more than a decade’s devotion. Thanks to more than ￥100 million R&D investment during the 12th Five-Year Plan period of China, the team obtained many leading achievements in both domestic and abroad, including:
1) High-Sensitivity Quantum-Magnetometry.
High-sensitivity magnetometry based on atomic ensemble is very effective technique for detecting weak magnetic anomaly signal. It has great applications potentially in geological prospecting, biomedicine and space science, et.al. Supported by the National Natural Science Foundation of China (NSFC) and National 863 Projects, the team has broken through core technologies of high signal-noise-ratio atomic cell, narrow-linewidth low-noise laser source with stabilized frequency and low-noise digital lock-in amplifier. Furthermore, independently, the team has successfully designed the prototype of quantum magnetometer whose sensitivity has been improved by more than two orders of magnitude compared with current magnetometer system and has reached the standard limit in national metrology and up to international advanced performance. The research achievement was selected and shown in 12th Five-Year National Science and Technology Innovation Achievement Exhibition and some technologies have been applied in commercial product. On June 2016, as the Chinese representative of Global Network of Optical Magnetometers for Exotic physics (GNOME), Prof. GUO gave an invited talk at UC Berkeley conference and formally joined the network on behalf of the Chinese site. In next five years, the team will have close cooperation with other several sites (such as UC Berkeley University in USA, University of Mainz in Germany, University of Freiburg in Switzerland, Jagiellonian University in Poland, KAIST in Korea) for detecting the dark matter with using high-sensitivity quantum magnetometer.
2) Quantum frequency and time dissemination.
Quantum frequency and time dissemination technology is one of the key technologies for the large-scale frequency and time network, which plays the important role in positioning and navigations. Peking University group proposed and demonstrated a novel frequency and time dissemination technology based on mode locked pulses. They have demonstrated world-level frequency and time dissemination over commercial 120 km long fiber. The measured instability of the frequency over the fiber is 6.19E-15/s and 11E-19 /day (overlapping Allan variance). This achievement has been shown in the Exhibition of 12.5 project achievements. The key innovative technologies are:
a) Innovative phase compensation method. The group proposed a new phase compensation method called the digital feed-forward technique. That is to compensate the phase error on user site by digital data communications, in contrast to the conventional way, which applied fiber stretcher or optical delay lines. The new technique is characterized of fast response and accurate phase correction.
b) Returned light separation and block method. Using DWDM technique the forward and feedback light transfer in different optical channels, so that it can separate the feedback signals from the interconnector reflections. The feedback light is generated by the nonlinear frequency shift technique so that on the user end there is no need to have a mode locked lasers.
3) Optical Frequency Standards.
Peking university group proposed and demonstrated the principle of active optical clock. Active optical clocks utilize a bad-laser cavity with cavity mode linewidth is much wider than that of the lasing gain profile. Compared with the recorded best super-cavity stabilized laser with Pound-Drever-Hall method, the center frequency of active optical clock is insensitive to the thermal Brownian motion noise, which is a formidable hurdle of available narrow linewidth laser light sources for next generation of optical clock with a linewidth of mHz. Our group have established different setups of active optical frequency standards based on lasing at 1469.9 nm in Cesium four-level configuration and lasing at 852 nm in Faraday laser configuration, and experimentally demonstrated the mechanism of lasing and suppressed cavity-pulling effect of active optical clock. The stability of best optical clocks may be improved by at least an order of magnitude using the mechanism of active optical clock. Peking University group proposed and demonstrated the compact Calcium atomic beam optical frequency standard with electron-shelving detection, and compact Rb optical frequency standard. Atomic optical clocks have reached to E-18 level uncertainty, however, with huge volume size, which limits the application of optical clock outside the lab. This group has realized a Calcium atomic beam optical frequency standard with higher stability of 3.0E-14 at 1 s and 2.9E-15 at 200 s, and the first compact optical frequency standard with full-sealed Calcium atomic beam vacuum tube. Moreover, this group has demonstrated a compact Rb optical frequency standard with a preliminary stability of 1.2E?14 at 1 s and 2.1 E?15 at 80 s. This group has been granted 18 Chinese/U.S./U.K Patents on quantum frequency standard and related techniques. The research of optical frequency standards is supported by the National Natural Science Foundation of China (NSFC), 863 Projects, and International Science & Technology Cooperation Program of China.
4) Quantum Filter Technology.
Ultra narrow bandwidth optical filter can be realized by using atomic transitions, which is stable and with narrow-band response. This filter is expected to improve the abilities to detect signal with special spectrum for space laser communication, space quantum communication, environmental component detection, atmospheric remote sensing and other applications. Our research team have begin the research since the 2006, and we have developed a series of atomic filters, which covers visible, near infrared, optical communication and other bands.
5) Quantum Communication.
Quantum communication is a way to achieve secure communication, whose security is guaranteed by the laws of quantum physics. It has become one of the hot research fields in the world, and it is at the stage of researching on real quantum communication systems and quantum networks with practical security. Our group aims at the key security problems existing in the practical quantum communication system, and proposes light source monitoring schemes to close the security loopholes in practical systems. Experiment has also been implemented by our group for the first time in the world. We also focus on the problem of generating true random number with quantum techniques, and propose several different generation schemes, including a bias-free scheme, a scheme with the longest bit length (14Gbit), one with the highest real-time generation rate (5.4Gbps) and one with the highest generation rate (1.6Tbps) reported in the world. We proposed passive light source monitoring schemes and implement the experiment in quantum communication, which has been cited for many times in articles written by an international authority, having been commented as “the only experimental implementation at present”. We propose new schemes to generate the true random number with a bias-free and long-length random sequence, which has been reported as breaking news by the international famous publication Laser Physics Letters. We propose a differential geometry optical method that can include multiple optical transmission effects. This method is commented as “a more general eikonal equation” by the international famous experts in optics. In addition, it can be used to correct the errors in optical designing accurately. The simulation software developed by this method has been applied to some major projects of laser engineering in China.
