Applications and Use Cases for the Quantum Internet

The Classical Internet has been constantly growing since it first became commercially popular in the early 1990's. It essentially consists of a large number of end-nodes (e.g., laptops, smart phones, network servers) connected by routers and clustered in Autonomous Systems. The end-nodes may run applications that provide service for the end-users such as processing and transmission of voice, video or data. The connections between the various nodes in the Internet include backbone links (e.g., fiber optics) and access links (e.g., WiFi, cellular wireless, Digital Subscriber Lines (DSLs)). Bits are transmitted across the Classical Internet in packets. Research and experiments have picked up over the last few years for developing the Quantum Internet . End-nodes will also be part of the Quantum Internet, in that case called quantum end-nodes that may be connected by quantum repeaters/routers. These quantum end-nodes will also run value-added applications which will be discussed later. The connections between the various nodes in the Quantum Internet are expected to be primarily fiber optics and free-space optical lasers. Photonic connections are particularly useful because light (photons) is very suitable for physically realizing qubits. Unlike the Classical Internet, qubits (and not classical bits or packets) are expected to be transmitted across the Quantum Internet. The Quantum Internet will operate according to quantum physical principles such as quantum superposition and entanglement . The Quantum Internet is not anticipated to replace, but rather to enhance the Classical Internet. For instance, quantum key distribution can improve the security of the Classical Internet; the powerful computation capability of quantum computing can expedite and optimize computation-intensive tasks (e.g., routing modelling) in the Classical Internet. The Quantum Internet will run in conjunction with the Classical Internet to form a new Hybrid Internet. The process of integrating the Quantum Internet with the Classical Internet is similar to, but with more profound implications, as the process of introducing any new communication and networking paradigm into the existing Internet. The intent of this document is to provide a common understanding and framework of applications and use cases for the Quantum Internet. This document represents the consensus of the Quantum Internet Research Group (QIRG). It has been reviewed extensively by Research Group (RG) members with expertise in both quantum physics and Classical Internet operation.

This document assumes that the reader is familiar with the quantum information technology related terms and concepts that are described in . In addition, the following terms and acronyms are defined herein for clarity: Bit - Binary Digit (i.e., fundamental unit of information in classical communications and classical computing). Classical Internet - The existing, deployed Internet (circa 2020) where bits are transmitted in packets between nodes to convey information. The Classical Internet supports applications which may be enhanced by the Quantum Internet. For example, the end-to-end security of a Classical Internet application may be improved by secure communication setup using a quantum application. Fast Byzantine Negotiation - A Quantum-based method for fast agreement in Byzantine negotiations . Hybrid Internet - The "new" or evolved Internet to be formed due to a merger of the Classical Internet and the Quantum Internet. Local Operations and Classical Communication (LOCC) - A method where nodes communicate in rounds, in which (1) they can send any classical information to each other; (2) they can perform local quantum operations individually; and (3) the actions performed in each round can depend on the results from previous rounds. Noisy Intermediate-Scale Quantum (NISQ) - NISQ was defined in to represent a near-term era in quantum technology. According to this definition, NISQ computers have two salient features: (1) The size of NISQ computers range from 50 to a few hundred physical qubits (i.e., intermediate-scale); and (2) Qubits in NISQ computers have inherent errors and the control over them is imperfect (i.e., noisy). Packet - Formatted unit of multiple related bits. The bits contained in a packet may be classical bits, or the measured state of qubits expressed in classical bits. Prepare-and-Measure - A set of Quantum Internet scenarios where quantum nodes only support simple quantum functionalities (i.e., prepare qubits and measure qubits). For example, BB84 is a prepare-and-measure quantum key distribution protocol. Quantum End-node - An end-node hosts user applications and interfaces with the rest of the Internet. Typically, an end-node may serve in a client, server, or peer-to-peer role as part of the application. If the end-node is part of a Quantum Network (i.e, is a quantum end-node), it must be able to generate/transmit and receive/process qubits. A quantum end-node must also be able to interface to the Classical Internet for control purposes and thus also be able to receive, process, and transmit classical bits/packets. Quantum Computer (QC) - A quantum end-node that also has quantum memory and quantum computing capabilities is regarded as a full-fledged quantum computer. Quantum Key Distribution (QKD) - A method that leverages quantum mechanics such as no-cloning theorem to let two parties (e.g., a sender and a receiver) securely establish/agree on a key. Quantum Network - A new type of network enabled by quantum information technology where qubits are transmitted between nodes to convey information. (Note: qubits must be sent individually and not in packets). The Quantum Network will use both quantum channels, and classical channels provided by the Classical Internet. Quantum Internet - A network of Quantum Networks. The Quantum Internet is expected to be merged into the Classical Internet to form a new Hybrid Internet. The Quantum Internet may either improve classical applications or may enable new quantum applications. Qubit - Quantum Bit (i.e., fundamental unit of information in quantum communication and quantum computing). It is similar to a classic bit in that the state of a qubit is either "0" or "1" after it is measured, and is denoted as its basis state vector |0> or |1>. However, the qubit is different than a classic bit in that the qubit can be in a linear combination of both states before it is measured and termed to be in superposition. The Degrees of Freedom (DOF) of a photon (e.g., polarization) or an electron (e.g., spin) can be used to encode a qubit.

The Quantum Internet is expected to be beneficial for a subset of existing and new applications. The expected applications for the Quantum Internet are still being developed as we are in the formative stages of the Quantum Internet . However, an initial (and non-exhaustive) list of the applications to be supported on the Quantum Internet can be identified and classified using two different schemes. Note, this document does not include quantum computing applications that are purely local to a given node (e.g., quantum random number generator).

Applications may be grouped by the usage that they serve. Specifically, applications may be grouped according to the following categories: Quantum cryptography applications - Refers to the use of quantum information technology for cryptographic tasks such as quantum key distribution and quantum commitment. Quantum sensors applications - Refers to the use of quantum information technology for supporting distributed sensors (e.g., clock synchronization). Quantum computing applications - Refers to the use of quantum information technology for supporting remote quantum computing facilities (e.g., distributed quantum computing). This scheme can be easily understood by both a technical and non-technical audience. The next sections describe the scheme in more detail.

Examples of quantum cryptography applications include quantum-based secure communication setup and fast Byzantine negotiation. Secure communication setup - Refers to secure cryptographic key distribution between two or more end-nodes. The most well-known method is referred to as Quantum Key Distribution (QKD) , which has been mathematically proven to be unbreakable. Fast Byzantine negotiation - Refers to a Quantum-based method for fast agreement in Byzantine negotiations , for example, to reduce the number of expected communication rounds and in turn achieve faster agreement, in contrast to classical Byzantine negotiations. This can be used for improving consensus protocols such as practical Byzantine Fault Tolerance(pBFT), as well as other distributed computing features which use Byzantine negotiations.

Examples of quantum sensor applications include network clock synchronization, high sensitivity sensing, etc. These applications mainly leverage a network of entangled quantum sensors (i.e. quantum sensor networks) for high-precision multi-parameter estimation . Network clock synchronization - Refers to a world wide set of atomic clocks connected by the Quantum Internet to achieve an ultra precise clock signal with fundamental precision limits set by quantum theory. High sensitivity sensing - Refers to applications that leverage quantum phenomena to achieve reliable nanoscale sensing of physical magnitudes. For example, uses an entangled quantum network for measuring the average phase shift among multiple distributed nodes, to achieve high-sensitivity and distributed quantum sensing.

Examples of quantum computing include distributed quantum computing and secure quantum computing with privacy preservation, which can enable new types of cloud computing. Distributed quantum computing - Refers to a collection of remote small capacity quantum computers (i.e., each supporting a relatively small number of qubits) that are connected and working together in a coordinated fashion so as to simulate a virtual large capacity quantum computer . Secure quantum computing with privacy preservation - Refers to private, or blind, quantum computation, which provides a way for a client to delegate a computation task to one or more remote quantum computers without disclosing the source data to be computed over .

The majority of routers currently used in the Classical Internet separate control plane functionality and data plane functionality for, amongst other reasons, stability, capacity and security. In order to classify applications for the Quantum Internet, a somewhat similar distinction can be made. Specifically some applications can be classified as being responsible for initiating sessions and performing other control plane functionality. Other applications carry application or user data and can be classified as data plane functionality. Some examples of what may be called control plane applications in the Classical Internet are Domain Name Server (DNS), Session Information Protocol (SIP), and Internet Control Message Protocol (ICMP). Furthermore, examples of data plane applications are E-mail, web browsing, and video streaming. Note that some applications may require both control plane and data plane functionality. For example, a Voice over IP (VoIP) application may use SIP to set up the call and then transmit the VoIP user packets over the data plane to the other party. Similarly, nodes in the Quantum Internet applications may also use the classification paradigm of control plane functionality versus data plane functionality where: Control Plane - Network functions and processes that operate on (1) control bits/packets or qubits (e.g., to setup up end-user encryption); or (2) management bits/packets or qubits (e.g., to configure nodes). For example, a quantum ping could be implemented as a control plane application to test and verify if there is a quantum connection between two quantum nodes. Another example is quantum superdense coding (which is used to transmit two classical bits by sending only one qubit). This approach does not need classical channels. Quantum superdense coding can be leveraged to implement a secret sharing application to share secrets between two parties. This secret sharing application based on quantum superdense encoding can be classified as control plane functionality. Data Plane - Network functions and processes that operate on end-user application bits/packets or qubits (e.g., voice, video, data). Sometimes also referred to as the user plane. For example, a data plane application can be video conferencing, which uses QKD-based secure communication setup (which is a control plane function) to share a classical secret key for encrypting and decrypting video frames. As shown in the table in , control and data plane applications vary for different types of networks. For a standalone Quantum Network (i.e., that is not integrated into the Internet), entangled qubits are its "data" and thus entanglement distribution can be regarded as its data plane application, while the signalling for controlling entanglement distribution be considered as control plane. However, looking at the Quantum Internet, QKD-based secure communication setup, which may be based on and leverage entanglement distribution, is in fact a control plane application, while video conference using QKD-based secure communication setup is a data plane application. In the future, two data planes may exist, respectively for Quantum Internet and Classical Internet, while one control plane can be leveraged for both Quantum Internet and Classical Internet.

The Quantum Internet will support a variety of applications and deployment configurations. This section details a few key use cases which illustrates the benefits of the Quantum Internet. In system engineering, a use case is typically made up of a set of possible sequences of interactions between nodes and users in a particular environment and related to a particular goal. This will be the definition that we use in this section.

In this scenario, two banks (i.e., Bank #1 and Bank #2) need to have secure communications for transmitting important financial transaction records (see ). For this purpose, they first need to securely exchange a classic secret cryptographic key (i.e., a sequence of classical bits), which is triggered by an end-user banker at Bank #1. This results in a source quantum node A at Bank #1 to securely establish a classical secret key with a destination quantum node B at Bank #2. This is referred to as a secure communication setup. Note that the quantum node A and B may be either a bare-bone quantum end-node or a full-fledged quantum computer. This use case shows that the Quantum Internet can be leveraged to improve the security of Classical Internet applications of which the financial application shown in is an example. One requirement for this secure communication setup process is that it should not be vulnerable to any classical or quantum computing attack. This can be realized using QKD which has been mathematically proven to be unbreakable. QKD can securely establish a secret key between two quantum nodes, without physically transmitting the key through the network and thus achieving the required security. However, care must be taken to ensure that the QKD system is safe against physical attacks which can compromise the system. An example of a physical attack is when an attacker is able to surreptitiously inject additional light into the optical devices used in QKD to learn side information about the system such as the polarization. Other specialized physical attacks against QKD have also been developed such as the phase-remapping attack, photon number splitting attack, and decoy state attack . QKD is the most mature feature of the quantum information technology, and has been commercially deployed in small-scale and short-distance deployments. More QKD use cases are described in ETSI documents . In general, QKD (e.g., ) without using entanglement works as follows: The source quantum node A transforms classical bits to qubits. Basically, for each classical bit, the source quantum node A randomly selects one out of two basis and uses the selected basis to prepare/generate a qubit for the classical bit. The source quantum node A sends qubits to the destination quantum node B via quantum channel. The destination quantum node receives qubits and measures each of them in one of the two basis at random. The destination quantum node informs the source node of its choice of basis for each qubit. The source quantum node informs the destination node which random quantum basis is correct. Both nodes discard any measurement bit under different quantum basis and remaining bits could be used as the secret key. Before generating the final secret key, there is a post-processing procedure over classical channels. For example, both nodes usually employ a part of the remaining bits to check if there were any errors and/or if there were an eavesdrop; another part of the remaining bits could be taken as the secret key. Basically, if an eavesdropper tries to intercept and read qubits sent from node A to node B, the eavesdropper will be detected due to the no-cloning theorem of quantum mechanics. As a part of the post-processing procedure, both nodes usually also perform information reconciliation for efficient error correction and/or conduct privacy amplification for generating the final information-theoretical secure keys. The post-processing procedure needs to be performed over an authenticated classical channel. In other words, the source quantum node and the destination quantum node need to authenticate the classical channel to make sure there is no eavesdroppers or man-in-the-middle attacks, according to certain authentication protocols such as . In , the authenticity of the classical channel is checked at the very end of the post-processing procedure instead of doing it for each classical message exchanged between the quantum source node and the quantum destination node. It is worth noting that: There are some entanglement-based QKD protocols such as , which work differently than above steps. The entanglement-based schemes, where entangled states are prepared externally to the source quantum node and the destination quantum node, are not normally considered "prepare-and-measure" as defined in ; other entanglement-based schemes, where entanglement is generated within the source quantum node can still be considered "prepare-and-measure"; send-and-return schemes can still be "prepare-and-measure", if the information content, from which keys will be derived, is prepared within the source quantum node the source quantum node before being sent to the destination quantum node for measurement. There are many enhanced QKD protocols based on . For example, a series of loopholes have been identified due to the imperfections of measurement devices; there are several solutions to take into account these attacks such as measurement-device-independent QKD . These enhanced QKD protocol can work differently than the steps of BB84 protocol . For large-scale QKD, QKD Networks (QKDN) are required, which can be regarded as a subset of a Quantum Internet. A QKDN may consist of a QKD application layer, a QKD network layer, and a QKD link layer . One or multiple trusted QKD relays may exist between the source quantum node A and the destination quantum node B, which are connected by a QKDN. Alternatively, a QKDN may rely on entanglement distribution and entanglement-based QKD protocols; as a result, quantum-repeaters/routers instead of trusted QKD relays are needed for large-scale QKD. Although the addresses of Source Quantum Node A and Destination Quantum Node B could be identified and exposed, the identity of users, who will use the secret cryptographic key for secure communications, will not necessarily be exposed during QKD process. In other words, there is no direct mapping from the addresses of quantum nodes to the user identity; as a result, QKD protocols do not disclose user identities. As a result, the Quantum Internet in contains quantum channels. And in order to support secure communication setup especially in large-scale deployment, it also requires entanglement generation and entanglement distribution , quantum repeaters/routers, and/or trusted QKD relays.

Secure computation with privacy preservation refers to the following scenario: A client node with source data delegates the computation of the source data to a remote computation node (i.e. a server). Furthermore, the client node does not want to disclose any source data to the remote computation node and thus preserve the source data privacy. Note that there is no assumption or guarantee that the remote computation node is a trusted entity from the source data privacy perspective. As an example illustrated in , a terminal node such as a home gateway has collected lots of data and needs to perform computation on the data. The terminal node could be a classical node without any quantum capability, a bare-bone quantum end-node or a full-fledged quantum computer. The terminal node has insufficient computing power and needs to offload data computation to some remote nodes. Although the terminal node can upload the data to the cloud to leverage cloud computing without introducing local computing overhead, to upload the data to the cloud can cause privacy concerns. In this particular case, there is no privacy concern since the source data will not be sent to the remote computation node which could be compromised. Many protocols as described in for delegated quantum computing or Blind Quantum Computation (BQC) can be leveraged to realize secure delegated computation and guarantee privacy preservation simultaneously. As a new client/server computation model, BQC generally enables: 1) The client delegates a computation function to the server; 2) The client does not send original qubits to the server, but send transformed qubits to the server; 3) The computation function is performed at the server on the transformed qubits to generate temporary result qubits, which could be quantum-circuit-based computation or measurement-based quantum computation. The server sends the temporary result qubits to the client; 4) The client receives the temporary result qubits and transform them to the final result qubits. During this process, the server can not figure out the original qubits from the transformed qubits. Also, it will not take too much efforts on the client side to transform the original qubits to the transformed qubits, or transform the temporary result qubits to the final result qubits. One of the very first BQC protocols such as follows this process, although the client needs some basic quantum features such as quantum memory, qubit preparation and measurement, and qubit transmission. Measurement-based quantum computation is out of the scope of this document and more details about it can be found in . It is worth noting that: The BQC protocol in is a circuit-based BQC model, where the client only performs simple quantum circuit for qubit transformation, while the server performs a sequence of quantum logic gates. Qubits are transmitted back and forth between the client and the server. Universal BQC in is a measurement-based BQC model, which is based on measurement-based quantum computing leveraging entangled states. The principle in UBQC is based on the fact the quantum teleportation plus a rotated Bell measurement realizes a quantum computation, which can be repeated multiple times to realize a sequence of quantum computation. In this approach, the client first prepares transformed qubits and send them to the server and the server needs first to prepare entangled states from all received qubits. Then, multiple interaction and measurement rounds happen between the client and the server. For each round, the client computes and sends new measurement instructions or measurement adaptations to the server; then, the server performs the measurement according to the received measurement instructions to generate measurement results (qubits or in classic bits); the client receives the measurement results and transform them to the final results. A hybrid universal BQC is proposed in , where the server performs both quantum circuits like and quantum measurements like to reduce the number of required entangled states in . Also, the client is much simpler than the client in . This hybrid BQC is a combination of circuit-based BQC model and measurement-based BQC model. It will be ideal if the client in BQC is a purely classical client, which only needs to interact with the server using classical channel and communications. demonstrates such an approach, where a classical client leverages two entangled servers to perform BQC, with the assumption that both servers can not communicate with each other; otherwise, the blindness or privacy of the client can not be guaranteed. The scenario as demonstrated in is essentially an example of BQC with multiple servers. How to verify that the server will perform what the client requests or expects is an important issue in many BQC protocols, referred to as verifiable BQC. discusses this issue and compares it in various BQC protocols. Measurement-based quantum computation is out of the scope of this document. provides a good introduction of measurement-based quantum computation. In , the Quantum Internet contains quantum channels and quantum repeaters/routers for long-distance qubits transmission .

There can be two types of distributed quantum computing : Leverage quantum mechanics to enhance classical distributed computing problems. For example, entangled quantum states can be exploited to improve leader election in classical distributed computing, by simply measuring the entangled quantum states at each party (e.g., a node or a device) without introducing any classical communications among distributed parties . Normally, pre-shared entanglement needs first be established among distributed parties, followed by LOCC operations at each party. And it generally does not need to transmit qubits among distributed parties. Distribute quantum computing functions to distributed quantum computers. A quantum computing task or function (e.g., quantum gates) is split and distributed to multiple physically separate quantum computers. And it may or may not need to transmit qubits (either inputs or outputs) among those distributed quantum computers. Pre-shared entangled states may be needed to transmit quantum states among distributed quantum computers without using quantum communications, similar to quantum teleportation. For example, has proved that a CNOT gate can be realized jointly by and distributed to multiple quantum computers. The rest of this section focuses on this type of distributed quantum computing. As a scenario for the second type of distributed quantum computing, Noisy Intermediate-Scale Quantum (NISQ) computers distributed in different locations are available for sharing. According to the definition in , a NISQ computer can only realize a small number of qubits and has limited quantum error correction. In order to gain higher computation power before fully-fledged quantum computers become available, NISQ computers can be connected via classic and quantum channels. This scenario is referred to as distributed quantum computing . This use case reflects the vastly increased computing power which quantum computers as a part of the Quantum Internet can bring, in contrast to classical computers in the Classical Internet, in the context of distributed quantum computing ecosystem . According to , quantum teleportation enables a new communication paradigm, referred to as teledata , which moves quantum states among qubits to distributed quantum computers. In addition, distributed quantum computation also needs the capability of remotely performing quantum computation on qubits on distributed quantum computers, which can be enabled by the technique called telegate . As an example, scientists can leverage these connected NISQ computer to solve highly complex scientific computation problems such as analysis of chemical interactions for medical drug development (see ). In this case, qubits will be transmitted among connected quantum computers via quantum channels, while classic control messages will be transmitted among them via classical channels for coordination and control purpose. Another example of distributed quantum computing is secure Multi-Party Quantum Computation (MPQC) , which can be regarded as a quantum version of classical secure Multi-Party Computing (MPC). In secure MPQC, multiple participants jointly perform quantum computation on a set of input quantum states, which are prepared and provided by different participants. One of primary aims of secure MPQC is to guarantee that each participant will not know input quantum states provided by other participants. Secure MPQC relies on verifiable quantum secret sharing . For the example shown in , qubits from one NISQ computer to another NISQ computer are very sensitive and should not be lost. For this purpose, quantum teleportation can be leveraged to teleport sensitive data qubits from one quantum computer A to another quantum computer B. Note that does not cover measurement-based distributed quantum computing, where quantum teleportation may not be required. When quantum teleportation is employed, the following steps happen between A and B. In fact, LOCC operations are conducted at the quantum computer A and B in order to achieve quantum teleportation as illustrated in . The quantum computer A locally generates some sensitive data qubits to be teleported to the quantum computer B. A shared entanglement is established between the quantum computer A and the quantum computer B (i.e., there are two entangled qubits: |q1> at A and |q2> at B). For example, the quantum computer A can generate two entangled qubits (i.e., |q1> and |q2>) and sends |q2> to the quantum computer B via quantum communications. Then, the quantum computer A performs a Bell measurement of the entangled qubit |q1> and the sensitive data qubit. The result from this Bell measurement will be encoded in two classical bits, which will be physically transmitted via a classical channel to the quantum computer B. Based on the received two classical bits, the quantum computer B modifies the state of the entangled qubit |q2> in the way to generate a new qubit identical to the sensitive data qubit at the quantum computer A. In , the Quantum Internet contains quantum channels and quantum repeaters/routers . This use case needs to support entanglement generation and entanglement distribution (or quantum connection) setup in order to support quantum teleportation.

Quantum technologies are steadily evolving and improving. Therefore, it is hard to predict the timeline and future milestones of quantum technologies as pointed out in for quantum computing. Currently, a NISQ computer can achieve fifty to hundreds of qubits with some given error rate. In fact, the error rates of two-qubit quantum gates have decreased nearly in half every 1.5 years (for trapped ion gates) to 2 years (for superconducting gates). The error rate also increases as the number of qubits increases. For example, a current 20-physical-qubit machine has a total error rate which is close to the total error rate of a 7 year old two-qubit machine . On the network level, six stages of Quantum Internet development are described in as follows: Trusted repeater networks (Stage-1) Prepare and measure networks (Stage-2) Entanglement distribution networks (Stage-3) Quantum memory networks (Stage-4) Fault-tolerant few qubit networks (Stage-5) Quantum computing networks (Stage-6) The first stage are simple trusted repeater networks, while the final stage are quantum computing networks where the full-blown Quantum Internet will be achieved. Each intermediate stage brings with it new functionality, new applications, and new characteristics. illustrates Quantum Internet use cases as described in this document mapped to the Quantum Internet stages described in . For example, secure communication setup can be supported in Stage-1, Stage-2, or Stage-3, but with different QKD solutions. More specifically: In Stage-1, basic QKD is possible and can be leveraged to support secure communication setup but trusted nodes are required to provide end-to-end security. The primary requirement is trusted nodes. In Stage-2, end-to-end security without relying on trusted nodes is possible to support secure communication setup too. The primary requirement is prepare-and-measure capability. In Stage-3, end-to-end security can be enabled based on quantum repeaters and entanglement distribution, to support the same secure communication setup application. The primary requirement is entanglement distribution to enable long-distance QKD. In Stage-4, Secure quantum computing with privacy-preservation can be enabled since it needs quantum memory for multiple rounds of quantum computation. Finally, in Stage-6, distributed quantum computing relying on more qubits can be supported.

Some general and functional requirements on the Quantum Internet from the networking perspective, based on the above applications and use cases, are identified as follows: Methods for facilitating quantum applications to interact efficiently with entanglement qubits are necessary in order for them to trigger distribution of designated entangled qubits to potentially any other quantum node residing in the Quantum Internet. To accomplish this specific operations must be performed on entangled qubits (e.g., entanglement swapping, entanglement distillation). Quantum nodes may be quantum end-nodes, quantum repeaters/routers, and/or quantum computers. Quantum repeaters/routers should support robust and efficient entanglement distribution in order to extend and establish entanglement connection between two quantum nodes. For achieving this, it is required to first generate an entangled pair on each hop of the path between these two nodes. Quantum end-nodes must send additional information on classical channels to aid in transmission of qubits across quantum repeaters/receivers. This is because qubits are transmitted individually and do not have any associated packet overhead which can help in transmission of the qubit. Any extra information to aid in routing, identification, etc., of the qubit(s) must be sent via classical channels. Methods for managing and controlling the Quantum Internet including quantum nodes and their quantum resources are necessary. The resources of a quantum node may include quantum memory, quantum channels, qubits, established quantum connections, etc. Such management methods can be used to monitor network status of the Quantum Internet, diagnose and identify potential issues (e.g. quantum connections), and configure quantum nodes with new actions and/or policies (e.g. to perform a new entanglement swapping operation). New management information model for the Quantum Internet may need to be developed.

This document provides an overview of some expected applications for the Quantum Internet, and then details selected use cases. The applications are first grouped by their usage which is a natural and easy to understand classification scheme. The applications are also classified as either control plane or data plane functionality as typical for the Classical Internet. This set of applications may, of course, naturally expand over time as the Quantum Internet matures. Finally, some general requirements for the Quantum Internet are also provided. This document can also serve as an introductory text to readers interested in learning about the practical uses of the Quantum Internet. Finally, it is hoped that this document will help guide further research and development of the Quantum Internet functionality required to implement the applications and uses cases described herein.

This document requests no IANA actions.

This document does not define an architecture nor a specific protocol for the Quantum Internet. It focuses instead on detailing use cases, requirements, and describing typical Quantum Internet applications. However, some salient observations can be made regarding security of the Quantum Internet as follows. It has been identified in that once large-scale quantum computing becomes reality that it will be able to break many of the public-key (i.e., asymmetric) cryptosystems currently in use. This is because of the increase in computing ability with quantum computers for certain classes of problems (e.g., prime factorization, optimizations). This would negatively affect many of the security mechanisms currently in use on the Classical Internet which are based on public-key (Diffie-Hellman) encryption. This has given strong impetus for starting development of new cryptographic systems that are secure against quantum computing attacks . Interestingly, development of the Quantum Internet will also mitigate the threats posed by quantum computing attacks against Diffie-Hellman based public-key cryptosystems. Specifically, the secure communication setup feature of the Quantum Internet as described in will be strongly resistant to both classical and quantum computing attacks against Diffie-Hellman based public-key cryptosystems. A key additional threat consideration for the Quantum Internet is pointed to by , which warns of the dangers of pervasive monitoring as a widespread attack on privacy. Pervasive monitoring is defined as a widespread, and usually covert, surveillance through intrusive gathering of application content or protocol metadata such as headers. This can be accomplished through active or passive wiretaps, traffic analysis, or subverting the cryptographic keys used to secure communications. The secure communication setup feature of the Quantum Internet as described in will be strongly resistant to pervasive monitoring based on directly attacking (Diffie-Hellman) encryption keys. Also, describes a method to perform remote quantum computing while preserving the privacy of the source data. Finally, the intrinsic property of qubits to decohere if they are observed, albeit covertly, will theoretically allow detection of unwanted monitoring in some future solutions.

The authors want to thank Mathias Van Den Bossche, Xavier de Foy, Patrick Gelard, Álvaro Gómez Iñesta, Wojciech Kozlowski, John Mattsson, Rodney Van Meter, Joey Salazar, and Joseph Touch, and the rest of the QIRG community as a whole for their very useful reviews and comments to the document.