Quantum computing is changing from a "toy" to a "tool"
— Interview with Pan Jianwei, Academician of Chinese Academy of Sciences and Professor of University of Science and Technology of China
Our reporter Bi Wenting
For the future development of quantum communication, on the one hand, it is necessary to expand the effective coverage of quantum communication networks, including the seamless connection of quantum communication networks and classical communication networks, the realization of quantum relays that can support thousands of kilometers, and the development of the next generation that can be all-day On the other hand, it is necessary to promote the independent research and development of core devices, the formulation of related application standards, and the large-scale application demonstration in the practice of engineering integration and verification.
More than 30 years ago, in the process of scientists' research on basic problems of quantum mechanics such as quantum superposition and quantum entanglement, fine quantum control technology gradually developed, which enabled human beings to leap from passive observation of quantum laws to active precise manipulation of quantum states. From this, what we now call "quantum technology" was born.
Quantum technology is an emerging discipline that combines quantum control and information technology.
In this field, my country has achieved a series of important scientific issues and breakthroughs in key core technologies, and achieved international leadership in some directions.
How will my country's quantum science and technology deepen its development, how will an independent innovation technology system be constructed, and how will the transformation from basic research to practicality and engineering achieve leading breakthroughs?
A reporter from Science and Technology Daily conducted an exclusive interview with Pan Jianwei, an academician of the Chinese Academy of Sciences and a professor at the University of Science and Technology of China, and asked him to talk about his thoughts on the development of quantum technology.
Will not replace the existing communication method Quantum communication will greatly improve the level of information security
Science and Technology Daily reporter: After the launch of the "Mozi" quantum science experimental satellite, Chinese scientists have used it to achieve a series of research results and successfully developed quantum communication to the practical stage. Does this mean a subversion of tradition? New communication method is about to be born?
Pan Jianwei: Although quantum communication is an emerging field, it is not intended to replace existing communication methods. On the contrary, it will use a new approach to greatly improve the security of existing information systems.
The core element of the modern information security system is the key. As long as the key is secured, the security of encrypted information can be guaranteed.
In traditional confidential communication, there is no method to strictly prove its security.
However, quantum secret communication can generate keys in real time through quantum key distribution in the existing public channels and distribute them to users safely and conveniently, so that if the information is eavesdropped during the transmission of the quantum key, the eavesdropper cannot do nothing. Leave a trace.
And this is absolute and guaranteed by the basic principles of quantum mechanics.
In other words, quantum secure communication uses quantum keys in traditional communication to improve security, rather than a complete subversion of traditional communication methods.
Science and Technology Daily reporter: At present, my country has built the first prototype of a quantum communication network integrating world and earth through the experiments of "Mozi" and "Beijing-Shanghai trunk line". my country's quantum communication is also at the international leading level.
So, in order to continue to maintain its leading position, what areas should my country focus on?
Pan Jianwei: The development goal of quantum communication is to build a global wide-area quantum communication network system.
First, the metropolitan area quantum communication network is realized through optical fiber, and then the connection between two neighboring cities is realized through the repeater, and finally the connection between the remote areas is realized through the satellite platform transfer. This is the development route of the wide area quantum communication network.
According to this route, the future development of quantum communication needs to expand the effective coverage of quantum communication networks on the one hand, including the seamless connection of quantum communication networks and classical communication networks, the realization of quantum relays that can support thousands of kilometers, and development The next generation of quantum satellite networks that can work around the clock; on the other hand, it is necessary to promote the independent research and development of core devices, the formulation of relevant application standards, and large-scale application demonstrations in the practice of engineering integration and verification.
There are 3 milestones in the development stage, the birth of a universal quantum computer may take 20 years
Science and Technology Daily reporter: In addition to quantum communication, quantum computing has also received extremely high attention. There are companies at home and abroad claiming to have entered the field of quantum computing, but there are also views that quantum computing is still far away.
What do you think for this?
Pan Jianwei: Quantum computing research is a highly complex task. As far as the academic community is concerned, it is still necessary to proceed step by step to achieve each staged goal.
There are several milestones in the development of quantum computing recognized by the international academic community——
The first milestone is to achieve the superiority of quantum computing, that is, the computing power of quantum computers for specific problems surpasses supercomputers, which requires coherent manipulation of about 50 qubits.
In 2019, Google's quantum computing prototype "Platanus" contains 53 superconducting qubits, surpassing supercomputers in solving random line sampling problems, which means that it has successfully realized the superiority of quantum computing.
However, solving random line sampling does not seem to have practical significance at present. The current quantum computing prototype is more like a "toy", which can only beat the classic computer in playing a certain game. Its important significance is that it proves the quantum computer. It can surpass classic computers.
The second milestone is the realization of a dedicated quantum simulator, that is, the coherent manipulation of hundreds of qubits, which is used to solve some practical problems that supercomputers cannot handle, such as quantum chemistry, new material design, and optimization algorithms.
At this time, quantum computers really start to be useful and become a "tool".
We hope to realize such a quantum simulator within 5-10 years, which is the main research task at present.
The third milestone is the realization of a programmable general-purpose quantum computer, that is, coherent manipulation of at least millions of qubits, and at the same time, the manipulation accuracy of qubits is improved to exceed the fault tolerance threshold (>99.9%), which can be used in classical password cracking and big data Search and artificial intelligence play a huge role.
At this stage, the quantum computer may be almost the same as the computer in our current concept, and it can be used to quickly solve many problems.
However, due to the huge technical challenges, it is not clear when a general-purpose quantum computer will be implemented. Academia generally believes that it will take 20 years or more.
Science and Technology Daily reporter: Not long ago, your team built the "Nine Chapters" of 76 photon quantum computing prototypes. According to media reports, it can achieve a task that a supercomputer can complete in 100 million years in 1 minute.
In your opinion, at what stage is my country's quantum computing?
Pan Jianwei: According to the existing optimal classical algorithm, the "Nine Chapters" process the Gaussian Bose sampling problem 100 trillion times faster than the current fastest supercomputer "Fuyue", marking that my country has also successfully achieved the superiority of quantum computing. The milestone of "Nine Chapters" is about 10 billion times faster than Google's "Plananus".
In addition to the light quantum system represented by the "Nine Chapters", ultra-cold atoms and superconducting circuits are also recognized as the most likely physical systems to achieve large-scale coherent manipulation of qubits.
In terms of superconducting quantum computing, my country is also expected to achieve "quantum computing superiority" beyond Google in the near future.
In the ultra-cold atom system, my country has made a series of important achievements in the preparation and manipulation of large-scale atomic entanglement, spin-orbit coupling, ultra-cold molecular reactions, etc. quantum simulation, which is to realize the special quantum simulation of ultra-cold atom system Machine laid the foundation.
Physical systems such as ions and silicon-based quantum dots also have the potential for multi-bit expansion and fault tolerance, and they are also the current hot topics of international quantum computing research.
In terms of the basic elements of quantum computing in these systems, my country has accumulated a large number of key technologies, which are on par with major international research forces.
In addition, due to the superiority of topological quantum computing in fault tolerance, the use of topological systems to realize universal quantum computers is an important long-term research goal. At present, domestic and foreign efforts are being made to realize single topological qubits. 0 to 1" breakthrough.
The rapid development of control technology, precision measurement has entered the quantum era
Science and Technology Daily reporter: In addition to the above two major areas, quantum precision measurement is also a very important subdivision of quantum technology. In contrast, the public may be relatively unfamiliar with it.
Could you please introduce the significance of quantum technology for precision measurement?
Pan Jianwei: Quantum state is highly sensitive to the environment, but it is actually a very sensitive sensor.
At the same time, the quantization of physical quantities also provides a very accurate benchmark. For example, photons are the smallest unit of light energy. At a certain frequency, the energy of a photon is a fixed value. Then if we can "count" photons one by one, The luminous intensity in the basic physical quantity can be defined by the number of photons, and the accuracy and stability will be greatly improved.
Here "counting" photons actually refers to the ability of quantum control.
It is precisely in view of the rapid development of quantum control and quantum information technology that the 26th International Conference on Metrology in 2018 passed a major resolution to define the international system of units by quantization.
In fact, many physical quantities such as time, position, acceleration, electromagnetic field, etc., can all be measured precisely beyond the limits of classical technology using quantum technology.
Science and Technology Daily reporter: What application areas does quantum precision measurement include?
Pan Jianwei: The main applications of quantum precision measurement include high-precision optical frequency standards and time-frequency transmission, quantum gyroscopes, atomic gravimeters and other quantum navigation technologies, as well as quantum sensitive detection technologies such as quantum radar, trace atom tracing, and weak magnetic field detection. .
These technologies will play an important role in a wide range of fields such as inertial navigation, next-generation time reference, stealth target recognition, global topographic mapping, and medical inspection.
There is still a certain gap in the field of quantum precision measurement in my country compared with developed countries. However, this gap has been narrowing rapidly in recent years, and in some directions it has reached the highest level of public reports in the world.
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related news
My scholar realizes edge detection of quantum metasurface image
Science and Technology Daily (Reporter Wu Changfeng) The reporter learned from the University of Science and Technology of China that the team of Guo Guangcan, an academician of the Chinese Academy of Sciences and the University of Science and Technology of China, has made important progress in the experimental research on edge detection of quantum metasurface images.
Professor Shi Baosen and Associate Professor Zhou Zhiyuan of Guo Guangcan’s team used high-quality polarization entanglement sources and high-efficiency medium metasurfaces to realize the remote switching of the image state to be detected between normal mode and edge detection mode, and confirmed that under weak light field illumination, Entangled photon illumination has a higher signal-to-noise ratio than direct single-photon illumination.
The results of this research will be published online in Science Advances at the end of 2020.
In recent years, the combination of metasurface materials and quantum optics has become an important research direction, and edge detection is a common method in image processing.
Compared with the traditional digital edge extraction method, the analog edge extraction method has higher speed and lower energy consumption, but there has been no related research on the edge detection of metasurface devices under quantum entanglement illumination.
In the process of this research, the researchers used linearly polarized light to irradiate the metasurface device to produce the optical spin Hall effect, which caused the two circularly polarized outgoing light fields to shift slightly in space, resulting in the middle part of the outgoing light field being linear. Polarization, the edge part is circular polarization, and then the edge contour of the object to be imaged can be extracted through the analyzer.
So, how can the imaging mode be remotely switched between the normal mode and the edge detection mode?
Experts explained that one photon in a polarization entangled light source can be used for illumination. The photon contains two possible polarization states. By measuring the state of the other photon, the polarization state of the photon used for illumination will also be determined. By remotely switching the polarization state of the photon used for triggering in the entangled photon pair, different imaging modes can be switched.
Experts said that the result is an attempt to detect the edge of an image in quantum metasurface research, and has potential applications in image encryption and steganography.
In addition, in scenarios where photon illumination is scarce, such as enzyme reaction tracking and observation of living organisms, a higher signal-to-noise ratio will show certain advantages.
This work will promote more research on the combination of quantum optics and metasurface materials.