Although the quantum information industry is still in its infancy, an ambitious “quantum internet” concept has become a serious issue. This year, the United States and the European Union have launched heavyweight quantum technology strategic documents, both with Quantum Networks and Quantum Internet as their visions.
This striking concept, which enables the current human vision of all quantum technologies, is the way to achieve “quantum cloud computing”, a platform for the transmission and storage of quantum information, a channel for the exchange of quantum ciphers that eavesdrop on traces, and a worldwide atomic clock that redefines time synchronization.
In this grand sense, although China is at the forefront of the world in quantum confidential communication networks, it has only taken the first step of “quantum Internet”. In particular, the relay site in the long-distance quantum confidential communication network is still not fully protected by quantum technology, which is also one of the main power points of international planning, which requires technological breakthroughs in the fields of quantum entanglement, space-based link, quantum storage and so on.
To make it easier to understand its subversive nature, the “quantum Internet” is often compared to the Internet, developed by the U.S. military in the 1960s and later flying into ordinary people’s homes. But just as quantum computers cannot replace classic computers, quantum Internet is not a substitute for the existing Internet, either for their underlying purposes or in terms of their economic costs.
Question 1: What is quantum Internet?
In the “U.S. Quantum Network Strategic Vision”, unveiled by the White House’s Office of National Quantum Coordination in February, the quantum Internet is described more generally as a vast network of quantum computers and other quantum devices.
The document specifically borrows the U.S. military’s first Internet to describe the disruptive vision of the quantum Internet: “It will catalyze many emerging technologies that will accelerate the growth of existing Internets, improve communication security, and dramatically transform computing technologies.” “
Pan Jianwei, a leading figure in quantum communication in China and a member of the Chinese Academy of Sciences, also drew up the quantum Internet with the classic Internet in an interview with the National Science Review (NSR) in 2019: “It is well known that the Internet is a global system for transmitting, processing and storing classical information. Quantum Internet can transmit, process and store quantum information in the same way. Qubits and quantum entanglement (the interconnected state of qubits) will be the basic resources of quantum Internet. “
A description of a strategic research agenda published in March by the European flagship quantum technology program,””European Quantum Agenda”, puts the two statements together: quantum computers, simulators and sensors are interconnected through quantum networks, distributing information and quantum resources (e.g., coherent, entanglement) to secure digital infrastructure.
We can conclude that the quantum Internet in the name of quantum, there are three main points: first, the network connection of the device is a quantum device, second, the network transmission of resources is quantum characteristics, and third, the way the network transmission depends on quantum mechanism.
Of course, advanced quantum devices such as commercial quantum computers are still far from being used, and the mature quantum Internet, which connects quantum computers, is generally a concept of the future.
Question 2: What is the relationship between quantum Internet and quantum confidential communication network?
At this stage, China is in the forefront of the world in the construction of quantum confidential communication network.
Pan Jianwei believes that the first practical task of quantum Internet is to share global keys in an unconditional and secure manner, that is, quantum information is completely tamper-proof.
If randomly generated ciphers are encoded in the quantum state of photons, an unknown quantum state cannot be accurately copied according to the quantum non-clone theorem and will be destroyed once measured. So once someone steals and tries to read the quantum key on their own, they’re sure to be discovered. The correct password information can only be obtained by using the “open mode” agreed upon by both parties.
Quantum non-clone theorem, while ensuring that this quantum key distribution (QKD) technology is eavesdropped, also creates engineering problems that cannot be enhanced like electrical signals. Photons are transmitted over long distances by optical fiber, which inevitably results in loss.
In 2017, the world’s first quantum confidential communication backbone line of more than 2000 kilometers, “Beijing-Shanghai Main Line”, set up 32 sites, the use of “trusted relay” program, through manual watch, network isolation and other means to ensure information security in the relay site.
Although “trusted relay” uses classical technology to prevent link node intrusion, the relay station is still the breakpoint of “quantum magic” compared to the theoretically proven security of quantum communication, and the current “quantum cipher” takes time to realize the “pure quantum link”.
Quantum confidential communication, on the other hand, transmits randomly generated quantum keys, not content information.
Compared with the previously described definition of quantum Internet, it can not connect quantum computers and other cutting-edge quantum devices, nor can it transmit quantum resources such as entanglement, the transmission mechanism has not achieved complete “quantumization”.
Zhao Yong, president of “Beijing-Shanghai Main Line” equipment supplier Kebigulian Shield Quantum Technology Co., Ltd. (hereinafter referred to as Guodun Quantum), believes that the quantum secret communication network based on quantum key distribution (QKD) is the initial stage of “quantum Internet”, the first to realize the application of information security, and the ultimate goal is to “full quantum network” and integrate the functions of quantum computing, quantum sensing and measurement into the quantum security network, distributed computation and quantum sensing network.
“From the beginning to the end, the positioning of information security applications runs through the quantum network, and quantum key distribution will be upgraded as the network escalates. He said.
Question 3: What key technologies do quantum Internet need?
The quantum Internet vision requires a comprehensive breakthrough in quantum communication, quantum precision measurement, quantum computing and other fields, and since some countries have begun to build a primary quantum confidential communication network, the most important thing is to solve the “distance” problem mentioned above.
On the one hand, the quantum repeater should be used to replace the artificially guaranteed relay station, and quantum entanglement should be used to realize the long-distance transmission of quantum state.
Simply put, the two quantums in the entanglement state, no matter how far apart, have an association in which one quantum state changes (for example, when people measure it), and the other state changes in a flash, as if it were telepathy.
Assuming that the receiver and sender of the information each have a photon, they each send a entangled photon as an “intermediary”, so that the two “intermediate” photons in the relay site entangled, then the two hands left photons will also form a entanglement relationship.
In this process, it is also necessary to solve the complex problems of quantum storage, quantum entanglement operation and so on, which is closely related to quantum computing. It can be said that the quantum repeater research will promote the development of quantum computing.
On the other hand, high-orbit satellites can be used as space-based relay sites, covering quantum networks over long distances. In 2017, Pan’s team successfully distributed a pair of entangled photons to two sites at a distance of 1,200 kilometers using the world’s first quantum communications experimental satellite, the Mozi.
NASA plans to build a space-based quantum link between Europe and North America in the mid-to-late 2020s, possibly using the ready-made International Space Station for demonstrations for precise time-sensitive photon distribution, wired.
Question 4: How are countries planning and progressing on the quantum Internet?
It is only after we understand the relationship between quantum confidential communication networks and quantum Internet, and understanding the importance of quantum relay technology and space-based links, it is easy to understand the planning of quantum Internet in the United States and Europe.
The White House Quantum Vision proposes that over the next five years, U.S. companies and laboratories will demonstrate the basic science and key technologies of quantum networks, from quantum interconnections, quantum repeaters, quantum memory to high-throughput quantum channels and the exploration of space-based entanglement distributions across intercontinental distances. At the same time, the potential impact of these systems and the application of improvements will be identified in order to reap commercial, scientific, health and national security benefits.
The vision for the next 20 years is for quantum Internet links to use networked quantum devices to realize new features that classical technology cannot achieve, while promoting human understanding of entanglement.
The European Quantum Flagship Project, with a total investment of 1 billion euros, believes that quantum networks are designed to go beyond short-range quantum key distribution, realize the full potential of quantum communication, and eventually move towards a global quantum Internet. Quantum repeaters are necessary in order to allocate entangled resources and implement more complex applications. Significant research and development investment is required in this regard.
The European Quantum Flagship Program, in its three-year vision, calls for the development of space-based quantum passwords using the QKD protocol and trusted node networks, and demonstrates a primary link that can be used as a module for future quantum repeaters.
Medium- and long-term goals (6 to 10 years vision) include: the use of quantum repeaters to demonstrate quantum communications over 800 km, the demonstration of quantum network nodes with at least 20 qubits, and the demonstration of entanglement using the Wei Starlink road.
China has not yet proposed a quantum Internet strategy, but in December 2019 the Central Committee of the Communist Party of China and the State Council issued the “Changjiang Delta Regional Integration Development Plan” clearly: “accelerate the development of the quantum communications industry, overall layout and planning and construction of quantum confidential communication trunk network, to achieve seamless docking with the national wide area quantum confidential communication backbone network, to carry out quantum communication application pilot.” “
In terms of project progress, in February this year, Pan Jianwei’s team demonstrated a 50-kilometer quantum memory entanglement in Hefei, setting a new world record.
The U.S. Department of Energy’ Argonne and Fermi National Laboratory, also in Illinois, are expected to be the first two nodes on the U.S. quantum Internet, and this summer will use a 30-mile-long section of fiber beneath the Chicago suburb to conduct a pilot exchange of quantum information and establish a two-way link.
A number of European research institutions have set up the Quantum Internet Alliance, which plans to complete a link demonstration of 3-4 quantum relay nodes in the Netherlands in recent years, charting a blueprint for the future pan-European quantum Internet.
Question 5: What are the future applications of quantum Internet?
Pan Jianwei said in an nSR interview that the invention of the Internet has brought humans into the information age, and that the quantum Internet will provide another opportunity to truly change the world.
For example, quantum computers will become an important part of the quantum Internet. Quantum computers are expensive to build, at least in the early days, to provide public services only through the quantum Internet. In this scenario, the user is able to access the quantum computer via the quantum Internet, upload the task and download the results by passing the qubit. This is also the concept of quantum cloud computing.
Mikhail Lukin, a quantum physicist at Harvard University, also said in a 2018 newspaper report in Nature that quantum computers need to be connected to exceed the size of hundreds of qubits at this stage.
Ronald Hanson, a Dutch scientist involved in the European Quantum Internet Alliance, adds that quantum cloud computing is also given quantum secrecy.
The European Quantum Internet Alliance also looks ahead to the transformative effects of quantum Internet in general science, such as the interconnection of distant atomic clocks, greatly improving time accuracy. Astronomers can also solve the problem of time synchronization in long-distance interference baselines, allowing distant telescopes to fit powerfully.
Question 6: Will the quantum Internet replace the existing Internet?
Just as scientists built quantum computers to better solve specific problems, not universal ones, the purpose of quantum Internet is not to replace the existing Internet, but also to replace the existing One.
The European Quantum Flagship program argues that quantum networks are compatible with and expanding existing digital infrastructure.
In practical application, quantum key distribution needs to be used in combination with cryptographic algorithm, and also needs to be done by “quantum channel and classical channel”: quantum channel transmission quantum signal, classical channel interaction from the extraction of security key processing method.
As a result, quantum confidential communication networks are often deployed on top of existing fiber-optic network infrastructure, such as telecom operators such as China Telecom.
Nicolas Gisin, of the University of Geneva in Switzerland, told Nature: “The internet can never be completely quantumd today. “
Some ideas are great at first glance, but they can be easily implemented without quantum technology, according to Norbert L?tkenhaus, a physicist at the University of Waterloo in Canada.
Zhao Yong told The News: Simplify understanding, the current Internet is “a global system for transmitting, processing and storing classical information”, and quantum Internet is the same for the transmission, processing and storage of quantum information. The “quantum Internet” is not an alternative to the existing Internet, but an infrastructure that superimposes new features on the Internet.