Academician Pan Jianwei's team: what is quantum communication, quantum precision measurement, and quantum computing
Recently, focusing on the theme of quantum information technology, learning times specially invited academician pan Jianwei's team to write three popular science articles: quantum communication: an important guarantee for the future independent and controllable information security ecology, quantum precision measurement: measurement accuracy breaking through the limits of classical technology, and quantum computing: solutions to improve computing power in the post-Moore era, A relatively complete introduction and Prospect of quantum information technology are given.
Quantum communication: an important guarantee for the future autonomous and controllable information security ecology
Author: Xu Feihu, Peng Chengzhi, pan Jianwei
Information security is a major strategic area related to the national economy and the people's livelihood. Traditional information security is realized by encryption algorithms that depend on computational complexity. However, with the rapid development of computing power, traditional encryption algorithms that depend on computational complexity are facing increasing security risks.
Quantum secure communication based on quantum key distribution is the only unconditionally secure communication mode in principle. Quantum key distribution refers to the use of quantum states to load information and generate keys through a certain protocol. The basic principle of quantum mechanics ensures that the key can not be eavesdropped, to realize secure quantum secure communication. The security of quantum secure communication is based on the basic principles of physics and has nothing to do with computational complexity. Even if the powerful quantum computer comes out in the future, it will not pose a threat to its security.
Quantum secure communication is the first quantum information technology to be applied and industrialized. The security key generated by quantum key distribution can be combined with a classical symmetric encryption algorithm in addition to the unconditionally secure "one-time encryption" encryption method in principle, taking into account security and communication rate. For example, according to the existing technical level, the combination of quantum key distribution and AES (Advanced Encryption Standard) encryption algorithm can achieve the communication rate of Gbps (switching bandwidth), greatly improve the update rate of seed key and effectively improve the communication security level. In addition, it can also be combined with the next generation of "PQC (anti-quantum computing password)" to enhance the security of identity authentication.
Development route of wide-area quantum communication
The development goal of quantum communication is to build a global wide-area quantum communication network system. The development route of a wide-area quantum communication network is to realize the metropolitan quantum communication network through optical fiber, then realize the connection between two adjacent cities through the repeater, and finally realize the connection between remote areas through the transfer of satellite platform.
In terms of metropolitan quantum communication networks, the University of science and technology of China has successively built the world's first all-around metropolitan quantum communication network, the first quantum government network, and the first large-scale metropolitan quantum communication network. In this process, relevant technologies have been developed and matured. The independently developed quantum confidential communication equipment has provided information security for many important activities.
In terms of an intercity quantum communication network based on the trusted relay, the international first long-distance optical fiber quantum secure communication backbone network "Beijing Shanghai trunk line" was put into operation at the end of 2016. With a total length of more than 2000 kilometers, the trunk line connects Beijing and Shanghai and runs through Jinan, Hefei, and other places. With the cooperation of finance, government affairs, electric power, and other departments along the line, carry out technical verification and application demonstration of long-distance quantum secure communication. Based on the application demonstration of the "Beijing Shanghai trunk line", the national development and Reform Commission approved the "national wide-area quantum secure communication backbone network" project in February 2018, which will cover important areas such as Beijing, Tianjin, and Hebei, the Yangtze River Delta, Guangdong, Hong Kong, Macao, Chengdu and Chongqing, and promote
In terms of satellite ground free-space quantum communication, with the support of the Chinese Academy of Sciences, the University of science and technology of China, together with the Shanghai Institute of Technical Physics of the Chinese Academy of Sciences, the Institute of microsatellite innovation, and other units, has successfully developed the world's first quantum science experimental satellite "Mozi". Launched in August 2016, "Mozi" took the lead in realizing satellite ground quantum communication in the world, and realized intercontinental quantum communication with a distance of 7600 kilometers for the first time, which fully verified the feasibility of realizing global quantum communication based on the satellite platform. Using the successful experience accumulated by Mozi, the development cost of the quantum satellite has been reduced from hundreds of millions of yuan to tens of millions of yuan. It is expected that the miniaturized quantum satellite will be launched in early 2022, laying the foundation for building a low-cost star cluster. The weight of the ground receiving station has also been reduced from more than ten tons to about 100 kg, which can initially support mobile quantum communication.
Combined with the "Mozi" quantum satellite and the "Beijing Shanghai trunk line", China took the lead in building the prototype of a wide area quantum secure communication network integrating heaven and earth, which has become a major landmark event in international quantum information research in recent years.
Application and popularization of quantum communication technology
On October 16, 2020, the central political bureau held in quantum science and technology research and the application prospect of 24th collective learning, learning hosted by xi Jinping, general secretary and pointed out that "the overall basic research, frontier technology and engineering technology research and development, to cultivate strategic emerging industries, such as quantum communication preemption quantum international competition commanding heights of science and technology, construction of the development of new advantage"."Beijing-shanghai Trunk Line" and "Micius" quantum satellite are both engineering integration and verification projects based on the basic and applied research results in the early period of more than 10 years in China, which have played a good demonstration effect for the independent research and development of core devices, the formulation of relevant application standards and large-scale application in the future. It has steadily promoted the application of quantum secure communication in commercial and national security fields.
In terms of core quantum communication devices, China Electronics Technology Group Co., Ltd., China University of science and technology, Shanghai Institute of microsystems and information technology, Chinese Academy of Sciences, etc. have realized the preliminary localization of main devices such as communication band single-photon detector and quantum random number generator, breaking the barrier of the foreign embargo. In the next two to three years, through the chip of key devices, the size of quantum encryption equipment can be reduced to the size of mobile phones and the cost can be greatly reduced.
As for the formulation of relevant application standards, with the active participation of more than 50 scientific research institutions and enterprises in China, national standards organizations such as China Communication Standardization Association, National Information Security Standardization Technical Committee, and password Industry Standardization Technical Committee focus on the interconnection, security evaluation and application services of quantum secure communication technology, Several national and industrial standards have been prepared. Chinese scholars have broken through the obstacles of western countries such as the United States and Canada, initiated and established the first international standardization organization covering the whole field of quantum information in the International Telecommunication Union, and are currently leading the preparation of several international standards.
Development prospect of quantum communication technology
In recent years, Chinese scholars have made several internationally influential achievements in the field of single-photon radar: breaking through the quantum efficiency limit of detecting infrared single photon at room temperature and realizing long-distance infrared single-photon atmospheric radar detection; It has realized the continuous detection of atmospheric wind field day and night and set a world record for the longest distance of single-photon imaging of 200 kilometers. At the same time, the use of single-photon radar can observe objects hidden outside the line of sight, that is, "nonfield of view imaging", and realize "partition viewing", which has a wide application prospect in the fields of counter-terrorism, riot prevention, emergency rescue and so on; The long-distance non field of view imaging is realized, and the imaging distance is increased from meter level to kilometer level for the first time, which greatly promotes the practical development of the non-field of view imaging technology. The single-photon detection technology developed in the research of quantum communication can also greatly improve the detection sensitivity, detection range, and resolution of traditional lidar, namely "single-photon radar". Single-photon radar can detect long-range and high-precision soft targets (atmosphere) and hard targets (objects). It has played an important role in the fields of ground mapping, long-range early warning, global situational awareness, air pollution detection and prediction, aerospace operations, and so on.
Thanks to the technical verification and application demonstration of wide-area quantum communication in china, network technology has initially met the requirements of practicality, the localization of core devices and the miniaturization of equipment have been initially realized, and the conditions for the first trial in key departments have been met. in the fierce international competitive environment, the current is the best time for China to accelerate the application of quantum secure communication and form an asymmetric advantage in information security as soon as possible. through about 10 years of effort, China is expected to build a complete wide-area quantum communication network technology system, providing an important guarantee for the formation of an independent and controllable national information security ecology in the future. (article published in learning times, January 19, 2022, 6th edition)
Quantum precision measurement: measurement accuracy pushes the limits of classical technology
Author: lu Zhengtian Pan Jianwei
Precision measurement is the basis of scientific research. it can be said that the entire modern natural science and material civilization are developed along with the continuous improvement of measurement accuracy. taking time measurement as an example, from the ancient sundial and water clocks to the modern mechanical clocks, and then to the modern quartz clocks and atomic clocks, with the continuous improvement of the accuracy of time measurement, communication, navigation, and other technologies can continue to develop, which not only brings great convenience to social life but also provides a weapon for new scientific discoveries. therefore, higher measurement accuracy has always been the goal of human beings.
With the breakthrough of basic research on quantum mechanics and the development of experimental technology, people have continuously improved their ability to manipulate and measure quantum states, so that they can use quantum states for information processing, transmission, and sensing. quantum precision measurement is the use of quantum mechanics, especially the consistency of the basic quantum system, to make high-precision and high-sensitivity measurements of some key physical quantities. using quantum precision measurement methods, people can obtain unprecedented measurement accuracy in physical quantities such as time, frequency, acceleration, and electromagnetic fields. it is precise because of the development of quantum regulation and quantum information technology that the 26th international conference on metrology in 2018 officially adopted a resolution to implement a new international unit definition from 2019, from physical measurement standards to quantum measurement standards, which marks that precision measurement has entered the quantum era.
Precise measurement of time frequencies
The measurement and application of high-precision time frequencies support the development of related scientific research, the operation of the economy and society, and the construction of national security systems. the high-precision time-frequency service system is a national strategic resource.
The frequency and time standards given by the atomic clock are the basic physical quantities with the highest measurement accuracy at present. At the same time, the improvement of the accuracy of the atomic clock also drives the improvement of the accuracy of another basic physical quantity measurement, physical constant definition, and physical law tests, and promotes the discovery of new physics and the progress of science and technology. Atomic clocks operating in microwave bands have been widely used in navigation, communication, and other fields. Each satellite in the widely used satellite positioning systems (such as China's Beidou navigation system, the United States' global positioning system GPS, etc.) carries multiple microwave band atomic clocks to give user positioning information by accurately measuring the arrival time of the signal. Due to its key role in the navigation system, the onboard atomic clock is known as the heart of the satellite navigation system. Chinese scientists are actively developing the next generation of higher precision spaceborne microwave atomic clocks. In 2018, the space cold atomic clock using laser cooling technology was realized for the first time in the world.
Due to the breakthrough in quantum precision measurement methods, atomic clocks (referred to as light clocks) running in the optical band have higher accuracy and stability and are expected to reach the order of 10-21 (that is, the error of trillions of years does not exceed 1 second). optical clock technology has developed rapidly in the past 20 years, for example, the strontium atomic light clock developed by us national bureau of standards has reached the order of 10-18 in terms of uncertainty and 10-19 instability, which is at least two orders of magnitude higher than the microwave atomic clock; the uncertainty and stability of the calcium ion light clock developed by Chinese scientists have entered the order of 10-18. at the same time, China has laid out the development of space light clocks, and the goal is to improve the accuracy of time-frequency measurements by two orders of magnitude in space. the new generation of time measurement and transmission technology will contribute to the generation of intercontinental light clock comparison and international "second" definition, and provide new methods for the detection of basic principles of physics such as gravitational wave detection and dark matter detection in the future. at the same time, the high-precision phase control and measurement of optical signals will also greatly improve the information transmission speed of future star-to-earth integrated quantum communication networks.
Quantum navigation
The inertial navigation system is an autonomous navigation system that does not rely on external information and does not radiate energy to the outside, which has the advantages of high concealment and full-time space work and has important application value in national security and other fields.
According to the best current classical inertial navigation technology reported publicly, the positioning error after 100 days of underwater navigation will reach the order of 100 kilometers, which is not enough to support long-term fully autonomous navigation. through the quantum regulation of atoms, quantum gyroscopes, and gravimeters based on atomic spin and cold atomic interference effects can achieve ultra-high sensitivity inertial measurements, which is expected to achieve a positioning error of less than 1 kilometer after 100 days of underwater navigation, and achieve long-term fully autonomous navigation. therefore, the navigation system based on quantum gyroscope and gravimeter has important applications in the fields of high-precision autonomous navigation and cutting-edge physics during the long-term voyage. in addition, high-precision gravity measurement can also be widely used in geodesy, resource exploration, and other fields.
At present, Chinese researchers have successfully developed a prototype of the atomic spin gyro principle, and the indicators are comparable to the highest indicators publicly reported abroad; the accuracy of the movable atomic gravimeter is close to the international first-class level, and the small mobile cold atom gravimeter has reached the best level of continuous gravity observation in the field at present, laying the foundation for the realization of a high-precision autonomous navigation system.
Single-quantum sensitive detection
The high sensitivity detection of single-photon, single-electron, single-atom, single-molecule, and other quantum systems has a wide range of application values and has become a hot frontier field of international physics research in recent years.
Single spin detection technology is widely used in quantum computing, life science, material science, and other fields. Using the solid-state single spin system represented by diamond NV color center, Chinese researchers have realized the magnetic field detection technology with high spatial resolution and high sensitivity at the same time and obtained the world's first magnetic resonance spectrum of a single protein molecule at room temperature, which provides a measurement basis for the study of biological problems at the level of single-molecule and single cell. This technology can also be used to explore the magnetic properties and magnetic structure of the micro-scale.
Single-atom detection technology has been widely used in earth science, environmental monitoring, and other fields. Chinese researchers have developed a new generation of laser atom well single atom sensitive detection method, which can count the extremely trace isotope atoms contained in environmental samples one by one, including krypton-81 isotopes with the content of only one billionth of a billionth in the air. this natural tracer is used to help understand global and regional water and ice cycles, to date millions of years of ancient groundwater and glaciers, and to provide key data for climate change research and water resource management.
Molecules contain multiple quantized degrees of freedom such as electron motion, vibration, and rotation, and single-molecule scale quantum systems exhibit very rich and novel quantum effects due to their strong spatial limits, structural symmetry, and significant discrete energy level structures. using the combination of scanning electron microscopy, atomic force microscopy, and Raman spectroscopy, Chinese researchers have comprehensively revealed the structure and changes of individual molecules on the surface, and achieved comprehensive characterization of single-molecule multiple specificities in single chemical bond accuracy.
In recent years, Chinese scholars have continuously caught up with the international advanced level in quantum precision measurement, and their technology has advanced by leaps and bounds, with remarkable results. for example, the key technologies in atomic clocks, quantum gyroscopes, and other aspects have approached the international advanced level; in terms of quantum radar, trace atom tracing, weak magnetic field measurement, etc., it has reached the international advanced level and has achieved several international leading achievements. with the continuous improvement of research level and the further enhancement of core competitiveness, the field of quantum precision measurement in china will play an important role in major strategic needs such as scientific research, economic life, and national security. (article published in learning times, February 16, 2022, 6th edition)
Quantum computing: a solution for increased computing power in the post-Moore era
Author: Zhu Xiaobo, Lu Chaoyang, Pan Jianwei
Quantum computing is a new computing model based on quantum mechanics, with a strong parallel computing capability far beyond classical computing in principle, providing solutions for large-scale computing problems required for artificial intelligence, cryptanalysis, meteorological forecasting, resource exploration, drug design, etc., and can reveal complex physical mechanisms such as quantum phase transitions, high-temperature superconductivity, and quantum hall effects.
Unlike traditional computers, which use bits of 0 or 1 to store information, quantum computing uses qubits as the basic unit for encoding and storing information. based on the superposition principle of quantum mechanics, a qubit can be a coherent superposition of two states of 0 and 1 at the same time, that is, it can be used to represent two numbers, 0 and 1. by extension, n qubits can represent the superposition of 2n numbers, so that a quantum operation can theoretically achieve parallel operations on 2n superimposed numbers at the same time, which is equivalent to 2n operations by classical computers. therefore, quantum computing offers an idea that fundamentally implements parallel computing, with the potential to greatly surpass the computing power of classical computers.
Similar to classical computers, quantum computers can also follow the framework of Turing machines, performing general quantum operations by performing programmable logic operations on qubits, thereby achieving a significant increase in computing power and even an exponential acceleration. A typical example is the rapid prime factorization quantum algorithm (Shor algorithm) proposed in 1994. The computational complexity of prime factorization is the basis for the widely used security of RSA public-key cryptography systems. For example, if you use a classical computer that calculates trillions of times per second to decompose a large number of 300 bits, it will take more than 100,000 years; If a quantum computer uses the same operation rate to execute Shor's algorithm only takes 1 second. Therefore, once the quantum computer is successfully developed, it will have a huge impact on the classical information security system.
The stage of development of quantum computing
The computational power of quantum computers grows exponentially with the number of qubits, so the core task of quantum computing research is the coherent manipulation of multiple qubits. according to the scale of coherent manipulation of qubits, the international academic community recognizes that quantum computing has the following stages of development:
The first stage is to achieve "quantum computing superiority", that is, the computational power of quantum computers for specific problems exceeds that of classical supercomputers, and achieving this goal requires coherent manipulation of about 50 qubits. in 2019, google took the lead in realizing the "quantum computing superiority" of the superconducting circuit system. China has achieved "quantum computing superiority" in optical quantum systems in 2020 and superconducting circuit systems in 2021. at present, China is the only country in the world to reach this milestone in two physical systems.
The second stage is to implement a dedicated quantum simulator, that is, coherent manipulation of hundreds of qubits, applied to specific problems such as combination optimization, quantum chemistry, machine learning, etc., to guide material design, drug development, etc. it takes 5 to 10 years to reach this stage and is currently the main research task.
The third stage is to implement a programmable general-purpose quantum computer, that is, coherent manipulation of at least millions of qubits, which can play a huge role in classical password cracking, big data search, artificial intelligence, and so on. since qubits are susceptible to environmental noise and errors, for large-scale qubit systems, ensuring the correct operation of the entire system through quantum error correction is an inevitable requirement and a major challenge for some time. due to the technical difficulty, it is not clear when a universal quantum computer will be implemented, and the international academic community generally believes that it will take 15 years or more.
At present, systematic research is being carried out on various physical systems that are expected to achieve scalable quantum computing. China has completed the research layout of all-important quantum computing systems and becomes one of the three countries (regions) with a complete layout, including the European Union and the united states.
Superconducting quantum computing achieves catch-up
At present, Google, IBM, and the University of Science and Technology of China are the top three superconducting quantum computing research in the world. In October 2019, after more than 10 years of continuous heavy investment in quantum computing, Google officially announced that the experiment proved the "superiority of quantum computing". They built a quantum processor containing 53 superconducting qubits, named "Sycamore." On the specific task of random line sampling, the Plane Tree exhibits computing power far beyond that of a supercomputer. In May 2021, the University of Science and Technology of China built the prototype "Zu Chong Zhi", which was the 62-bit superconducting quantum computing prototype with the largest number of qubits in the world at that time, and realized programmable two-dimensional quantum walking. On this basis, the 66-bit "Zu Chong No. 2" was further realized. "Zuchong No.2" has the programming ability to execute arbitrary quantum algorithms and realizes the rapid solution of quantum random line sampling. According to the optimized classical algorithm that has been published so far, the processing speed of the quantum random line sampling problem of "Zuchong-2" is 10 million times faster than that of the fastest supercomputer, and the computational complexity is 1 million times higher than that of Google's "plane wood".
Quantum computing research on other systems
Physical systems such as ions and silicon-based quantum dots also have the potential for multi-bit expansion and fault tolerance and are also the hot directions of international quantum computing research. China started late in the quantum computing research of ion systems and is currently in a state of catching up as a whole, and the dominant research units in china include Tsinghua university, the university of science and technology of china, and the national university of defense technology, etc., which have accumulated a large number of key technologies in the preparation of ion traps, single-ion coherence retention time, high-precision quantum logic gates, multi-bit quantum entanglement and other basic elements of quantum computing. China is at the same level as the main international research force in the direction of quantum computing of silicon-based quantum dots. in addition, due to the superiority of topological quantum computing in fault tolerance, the use of topological systems to achieve universal quantum computing is an important international long-term research goal. at present, both at home and abroad are working hard to achieve the breakthrough of "0 to 1" of a single topological qubit.
The future of quantum computing
After achieving the stage goal of "the superiority of quantum computing", the future development of quantum computing will focus on two aspects: first, continue to improve the performance of quantum computing. To realize fault-tolerant quantum computing, the primary consideration is how to expand the scale of quantum computing systems with high precision. When realizing the expansion of qubits, the number and quality of bits are extremely important. Each link of the experiment (preparation, manipulation, and measurement of quantum states) needs to maintain high precision and low noise. With the increase of the number of qubits, the errors caused by noise, crosstalk, and other factors also increase, which is of great significance to the design of quantum system Processing and regulation have brought great challenges, which still needs a lot of concerted efforts of science and engineering. The second is to explore the application of quantum computing. It is expected that quantum computing is expected to break through thousands of bits in the next five years. Although fault-tolerant general quantum computing cannot be realized, for the time being, scientists hope to explore the application of quantum computing to machine learning, quantum chemistry, and other fields in the stage of noisy quantum computing (nisq). (the article was published in the 6th edition of learning times on March 2, 2022)
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