How to Meet the Quantum Internet The six stages of development of the quantum Internet
In 1969, the U.S. military created the ARPA Network, the predecessor of the Internet; more than 50 years later, the U.S. military is focusing on another transformative technology, the quantum Internet. In this article, three U.S. military figures, Lubjana Beshaj, Samuel Crislip and Travis Russell, discuss the route to the quantum Internet.
In the 1980s, Richard Feynman famously came up with the idea of a computer that uses quantum mechanics for computation [1]. Feynman observed that the computers of his time had difficulty modeling complex molecular systems, but if computers used the laws of quantum mechanics, they could easily model molecular systems. The concept of quantum computers was well established in academia by the mid-1990s, when mathematician Peter Shor discovered a polynomial-time algorithm that could quickly decompose large numbers [2]. It was soon discovered that this algorithm would break many encryption schemes that were previously considered very secure and widely used by quickly computing decryption keys.
Recent advances in quantum technology by various countries and teams have transformed quantum computers from an idea to a working prototype. While computers capable of implementing Shor's algorithm may still be years away, stakeholders in government and industry have largely recognized the need to prepare for a quantum future. The most obvious feature of this action is that agencies such as the National Institute of Standards and Technology (NIST) are racing to develop secure quantum-resistant cryptographic schemes that will be less likely to be affected when quantum computing is fully implemented [3], yet less attention has been paid to the infrastructure needed to support the use of quantum computer networks.
Based on what experts have said, this paper will discuss how the quantum Internet might evolve. Following the model proposed by Stephanie Wehner, David Elkouss and Ronald Hanson, this paper divides this development into six stages [4]. Each stage introduces a new technology that makes the Internet "more quantum" than the previous stage. In discussing each stage of development, this paper will highlight technologies and trends of interest to the DoD. The increasing DoD interest in quantum technologies and a viable quantum Internet may lead to innovations in secure communications, quantum sensing, clock synchronization, and other as-yet-undiscovered technology areas.
It is important to emphasize that this paper details the model proposed by Wehner, Elkouss, and Hanson, and while other models may exist, an alternative version has not been proposed because the actual way in which the quantum Internet may develop is completely unknown. For each of the six phases described, a new technology is introduced thereby addressing the vulnerabilities of the previous phase. This paper does not discuss the potential cost or return on investment in these technologies, but only describes them qualitatively. Nor will this paper speculate on when these technologies will become widely available, as there are already many answers to this question in the various literatures.
The future viability of the quantum Internet may shape new strategic environments, including key operational domains in which competition, conflict, or combat takes place. These military operations are sometimes referred to interchangeably as multi-domain or full-domain operations (MDO/ADO): the United States already considers land, sea, air, space, and cyber as operational domains within MDO/ADO [5].
The quantum Internet is particularly applicable to the cyber domain because it requires many of the physical components of the current Internet, along with the expansion of many assets and the inclusion of new technologies. As the DoD and government invest in developing the quantum Internet or securing its access, they will witness growth in their cyber domain capabilities, which will translate into advantages in other operational domains due to the interwoven nature of MDO/ADO.
01Quantum Technology and the Quantum Internet
This paper considers the term Quantum Internet to refer to any network of computer systems or communication devices employing inherently quantum technology, and it does not necessarily refer to a new Internet separate from the current Internet; rather the term refers to an emerging infrastructure that will be intertwined with the existing Internet. Once the technology is developed, a quantum Internet may be needed to communicate between fully operational quantum computers. But the quantum Internet will enable much more than the integration of quantum computers, and that alone may not be possible for many years. A quantum Internet or even the addition of quantum components to the existing Internet, allowing for the future integration of quantum computers into the existing Internet, would then make possible a whole new kind of information transmission and storage, which is colloquially known as quantum information.
Whereas classical information is encrypted and stored as a sequence of bits, i.e. strings of zeros and ones, quantum information is encoded as the state of a system of quantum bits. A single quantum bit is a quantum state of a particle in a superposition of pairs of possible states, usually considered as a mixture of 0s and 1s. In fact, although other possibilities have been investigated, quantum bits are usually encoded as the polarization of a photon or the spin of an electron. By accessing multiple quantum bits, the whole system may become "entangled", so that the state of one quantum bit is closely related to the state of another (potentially remote) quantum bit. In this way, computations performed on different quantum bits at distant locations may interfere and affect each other instantaneously [6].
The laws of quantum mechanics endow quantum information with many properties that distinguish it from classical information and may give rise to new applications. For example, the unclonable theorem of quantum mechanics makes it impossible to design a device that takes one quantum bit as input and produces two copies of the same quantum bit as output. In other words, an eavesdropper who intercepts a quantum bit during transmission cannot copy the quantum bit and send the original quantum bit to the terminal without being detected. In addition, the measurement principle of quantum mechanics suggests that if an eavesdropper measures any property of a quantum bit in transmission, the state of the quantum bit changes and this change can be detected at reception, so the manipulated quantum bit can be discarded. Entanglement may be applied to many scenarios, such as new clock synchronization protocols and exploiting existing correlations between remotely entangled quantum bits [7]. In conclusion, the quantum Internet has the potential to change not only the infrastructure of the network domain, but also the nature of the information stored and transmitted in the infrastructure.
Although the exact process by which the existing Internet will evolve into a quantum Internet is unclear, experts have recently weighed in on what the process might entail [8]. In what follows, this paper describes the six stages of development that are expected to occur with the advent of the quantum Internet. At each stage a new technology will be introduced that will provide additional functionality to the quantum Internet. In addition to a summary of these stages, this paper discusses how the new technologies introduced at each stage will affect DoD interests and what steps the DoD might consider taking to implement them? What technologies already exist and how different individual and government actors might invest in them?
02Trusted Repeater Phase
Figure 1 Quantum key distribution
In the first stage of quantum Internet development, the Internet still transmits only classical information, however it can do so more securely by integrating quantum repeaters into the existing infrastructure. In this stage, a pair of quantum repeaters only needs the ability to execute a single quantum protocol, known as quantum key distribution (QKD; see Figure 1).
This protocol allows the generation of keys that are securely distributed to neighboring quantum repeaters [9]. Classical messages can be encoded at one repeater, securely transmitted to the next repeater and finally decoded. This process can be performed between each pair of consecutive repeaters, each of which generates a new key that ensures the transmission of classical messages from end A to end B by linking multiple repeaters together. Trusted repeaters require that messages are decodable at each repeater. Thus, secure transmission relies on the trustworthiness of the repeater sequence. The advantage of transmitting messages in this way is that messages can be secured between repeaters even in the presence of an eavesdropper. The message cannot be decoded without the key, and the security of the key distribution between the repeaters is guaranteed by the laws of quantum mechanics, not by the computational difficulty of the decryption process. In other words, both now and in the future, intercepted messages cannot be decoded except by guessing the key, even with the help of powerful computers or even quantum computers [10].
Investment in the trusted repeater stage is crucial for the DoD because it facilitates secure communications that overcome traditional adversarial interception techniques. The military application of this phase will allow geographically dispersed commanders and subordinates to exchange operational details without fear of interception. This state of affairs increases adversarial capabilities on the battlefield and may also lead to the failure of traditional direction finding, a method or signal interception technique that intercepts the communication path to track the originator's location. This phase will also "sound the alarm" to alert other outsiders in the communications chain who are attempting to access these secure transmissions so that appropriate action can be taken to prevent further interceptions. Ultimately, increasing security, defeating interception, and reducing or eliminating transmitter detection will provide commanders and forces with a more secure environment and a greater chance of success.
If DoD focuses on increasing the capabilities of trusted relays, it may also facilitate more secure intelligence delivery in a deployed environment that does not rely on traditional intelligence networks. Traditional intelligence delivery techniques rely on complex security networks, which can also be daunting tasks in combat operations. While there is an option for intelligence exchange via traditional means, this method typically requires encryption, dedicated transmission channels, and considerations for the use of codewords or values, all conditions that delay the receipt of intelligence. Such obstacles can be detrimental to the commander's decision cycle, disrupting the validity of the intelligence while potentially forcing decisions without the necessary information. However, a quantum Internet with trusted relays can provide the fast and secure intelligence transmission environment necessary for commanders in an operational environment.
03Preparation and Measurement Phase
In the second phase of the quantum Internet, the Internet can prepare individual quantum bits at the initial node and transmit them to the final node for measurement. This is the first stage in which the Internet can truly be considered quantum, as it is now capable of transmitting information in the form of quantum bits. It is important to note that successful quantum bit transmission is unlikely at this stage. Due to the possibility of loss of the quantum bit, the receiver must detect if the quantum bit has been received before the measurement. Therefore, all measurements are "post-selected" after the successful transmission of the quantum bit is known. The requirement of detecting successful transmission implies some restrictions on the set of enforceable protocols, since any measurement of a quantum bit necessarily disturbs its state [11]. Nevertheless, even with the ability to transmit quantum bits in this imperfect manner, important protocols, such as end-to-end QKD, can be implemented without relying on trusted relays [12].
The preparation and measurement phase requires the DoD to recognize the limitations of quantum transmission and the investments necessary to ensure a secure quantum Internet. The United States is lagging behind China in the use of quantum technology, putting China on the path to initial success in quantum Internet, quantum communications, and quantum sensing. China has completed the "Beijing-Shanghai trunk line" for quantum communications between Shanghai, Beijing, and other cities [13]. While this success does not clearly indicate a successful example of the quantum Internet, it does highlight the progress being made in China, while the United States has focused primarily on the development of quantum computing and has not fully advanced the infrastructure needed for the quantum Internet.
The second phase further establishes the principle of quantum sensing and its utility on the battlefield, as tactical surprise can set the stage for successful military operations. The concept of quantum sensing in this phase is possible when evaluating perturbations of quantum states. For example, quantum radar developed by Jonathan Baugh at the University of Waterloo, Canada, can measure quantum states in microwave beams and detect anomalies [14]. In military applications, the accuracy of quantum measurements would allow immediate and specific detection of combat assets, such as stealth fighters or submarines. The first military to develop such a radar would increase its effectiveness in early warning and target capture.
04Entanglement generation phase
Figure 2 Entanglement distribution
In the third stage of development, the Internet can generate a pair of maximally entangled quantum bits and distribute them to node A and node B. This process must succeed with near unit probability. This stage bypasses the post-selection requirements of the previous stage and allows for a wider variety of protocols to be performed between Node A and Node B. This phase can be implemented using a real quantum relay whose function is to receive a quantum bit, entangle it with another quantum bit, and pass a second quantum bit (see Figure 2). This "daisy chain" of entangled quantum bits leads to the distribution of entanglement between the initial and final nodes of the chain [15]. The successful distribution of entangled quantum bits allows nodes to securely transmit quantum bits using a process called quantum invisible transfer. In addition, new and more secure forms of QKD are now available between end nodes, and the security of these new QKD protocols will no longer require end users to trust even their own measurement devices [16], increasing their security.
During this phase, the DoD will begin to enable instantaneous communications regardless of the capacity of the data stream, a key component of promoting military advantage through a more coordinated and instantaneous information environment. Dominance in the operational environment is focused on forces, weapons, and systems that can be maneuvered, reacted, defended, and destroyed based on the commander's choice of time and space, as well as the safeguarding of communications systems. During the entanglement generation phase, the commander has access to terminal nodes that allow secure and near-instantaneous transmission, thus providing forces with instantaneous synchronization of superior forces, especially when simultaneous non-dynamic and dynamic effects are required to achieve specific objectives, as time becomes critical when conducting immediate, uninterrupted communication. These issues demonstrate the urgency of investment and research in achieving a robust quantum Internet.
05Quantum storage stage
The next stage is crucial for the realization of large quantum networks. The main difference between this stage and the previous one is that in this newer stage, multiple quantum bits can be moved from one network node to another. Quantum memory allows the network to create one state at a time, storing the quantum states received from the network. This approach makes it possible to send larger quantum bits through quantum invisible transfer states, increasing the amount of quantum information that can be transmitted. Moreover, at this stage, quantum clock synchronization and quantum anonymous transmission become feasible through multi-party entanglement systems [17]. Entanglement and quantum communication ensure that the time signature between multiple parties is authentic, improving the security of communication transmissions [18].
The military will benefit from this phase of advancement by maximizing its ability to further synchronize operations in large-scale conflicts through more accurate clock synchronization than was possible with the previous phase of communication gains. Clock synchronization translates into accuracy in time calibration and GPS fidelity, which are key components to achieving military objectives in time and space. The Defense Advanced Research Projects Agency (DARPA) noted the potential for improvements in quantum synchronization, which can increase efficiency from parts per billion to parts per trillion of a second [19]. This improvement may seem inconsequential, but any improvement in accuracy could mean success or failure on the battlefield. Major Matthew Myer, USA, emphasized this point from an infantry perspective: as ground forces rely on air platforms to defeat the enemy in close missions, the close proximity of friendly and enemy forces may result in fratricidal events during missions, and pilots must frequently change tactics and weapon systems thereby adapting to the situation [20]. Relying on life-saving measures or the availability of weapon systems allows everyone to acknowledge any improvement in accuracy and timeliness.
06Few quantum bits fault-tolerant stage
Possibly at a lower level, fault-tolerant designs allow the system to continue its intended operation without failing completely when some part of the system fails. The term "few quantum bits" here means that the number of available quantum bits is so small that the end node itself can be simulated on a classical computer [21]. However, a classical computer may not be able to simulate the entire network. Stable quantum bits are difficult to design, but the standard fault-tolerance scheme uses seven or more physical quantum bits to encode each logical quantum bit, requiring more quantum bits for error correction [22]. The huge engineering makes it very difficult to test fault-tolerant schemes that contain multiple coded quantum bits. Accessing fault-tolerant gates through quantum computer networks interconnected by quantum and classical channels allows for more accurate clock synchronization as well as distributed quantum computing because quantum computers are interconnected by quantum channels and users can use entanglement to enable increased computational power. In addition, small quantum computers connected by quantum links could be the basis for future large-scale quantum computers. As researchers working on the Google machine recently demonstrated, even in this limited case, users can perform computations at speeds that are not possible with current quantum computers [23].
A fault-tolerant design could provide the DoD with a viable quantum network that it could rely on in environments that are not covered by satellites, allowing troops to continue executing operations even in the event that an adversary attempts to disrupt the military's satellite connection. The Pentagon is aware of this situation as a realistic vulnerability and understands the benefits that quantum offers in overcoming that, but the U.S. investment in bringing this maturity is a fraction of the budget that another quantum giant, China, has committed to quantum development [24]. Therefore, in order to reach this stage and achieve fault-tolerant designs durable enough to survive the brutal conditions on the front lines, the United States must continue to advance quantum computing and networking expertise through initiatives such as the Million Dollar International Quantum U Technology Accelerator, a Navy and Air Force interagency-supported activity that reviews proposals from experts to develop future quantum-capable competitions for the U.S. Department of Defense, while fostering technology collaboration, innovation, and incubation [25].
07Quantum computing phase
The final stage allows the implementation of all protocols that will provide secure communication, secure login networks, quantum enhanced GPS, secure voting, quantum digital signatures, gravitational wave detection, and more. But having a mature quantum computer at the end of each node has both advantages and risks. One of the main risks is to break the currently existing cryptography, where the Shor algorithm solves the discrete logarithm problem by using a quantum computer to decompose a large integer [26]. With the advent of such quantum algorithms, as well as quantum computers and the quantum Internet, adversaries will break commonly used public-key cryptosystem schemes (e.g., RSA, DSA [Digital Signature Algorithm], and ECC [Elliptic Curve Cryptography]) relying on the computational difficulty of such factorization problems.
If quantum computing stages are implemented, then each of the previous stages can be leveraged, along with access to a quantum computer system that can provide the level of analysis a commander needs to succeed in any operational environment. A mature quantum Internet means that quantum systems can be accessed in a timely manner via the Internet, providing powerful computing capabilities to analyze all possible data points that a commander can use to help in the decision cycle. Quantum computers can find optimal solutions faster than any classical computer. Moreover, the potential problems that quantum computers can solve remain unfathomable, meaning that the ability of quantum computers to provide real-time assistance on the battlefield could change the nature of warfare in ways we do not understand. However, the military can only succeed in the quantum environment if it chooses to invest in the quantum Internet now.
The DoD and other stakeholders should view the development of the quantum Internet as a staged process, rather than as a single entity that will emerge once quantum computing becomes viable. By tracking and analyzing the staged development of the quantum Internet, the DoD can keep pace with technological advances in the national and private sectors and thus be well prepared for the eventual emergence of quantum computing. Conversely, ignoring this development and fighting the eventual emergence of quantum computers only by investing in anti-quantum technologies will put it at a disadvantage compared to other nations and individual participants.
Link to article.
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References：
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[25]Ibid.
[26]Shor, “Algorithms for Quantum Computation,” 124–134.
