Applications and Use Cases for the Quantum Internet
draft-wang-qirg-quantum-internet-use-cases-03

Abstract

The Quantum Internet has the potential to improve Internet application functionality by incorporating quantum information technology into the infrastructure of the overall Internet. In this document, we provide an overview of some applications expected to be used on the Quantum Internet, and then categorize them using the standard telecommunications classification of control plane versus data plane functionality. Other classification schemes are also possible and discussed briefly. We then provide detailed use cases for selected applications, and then derive a few key requirements for the Quantum Internet. The intent of this document is to provide a common understanding and framework of applications and use cases for the Quantum Internet.

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Table of Contents

• 1. Introduction
• 2. Conventions used in this document
• 3. Terms and Acronyms List
• 4. Quantum Internet Applications
• 4.1. Overview
• 4.2. Control vs Data Plane Classification
• 4.2.1. Control Plane Applications
• 4.2.2. Data Plane Applications
• 4.3. Other Possible Classifications
• 5. Selected Quantum Internet Use Cases
• 5.1. Secure Communication Setup
• 5.2. Distributed Quantum Computing
• 5.3. Secure Quantum Computing with Privacy Preservation
• 6. General Requirements
• 7. Conclusion
• 8. IANA Considerations
• 9. Security Considerations
• 10. Acknowledgments
• 11. Informative References
• Authors' Addresses

1. Introduction

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. The end-nodes run applications that provide some value added service for the end-users such as processing and transmission of voice, video or data. The physical connections between the various nodes in the Internet include Digital Subscriber Lines (DSLs), fiber optics, etc. Bits are transmitted across the classical Internet in packets.

Research and experimentation have picked up over the last few years for developing a Quantum Internet [Wehner]. It is anticipated that the Quantum Internet will provide intrinsic benefits such as better end-user and network security. The Quantum Internet will have end-nodes, which may be connected by quantum repeaters/routers. These quantum end-nodes will also run value-added applications which will be discussed later.

The physical connections between the various nodes in the Quantum Internet are expected to be primarily fiber optics and free-space optics. Optical connections are particularly useful because light (photons) is very suitable for physically encoding qubits. Unlike the classical Internet, qubits (and not classical bits or packets) are expected to be transmitted across the Quantum Internet due to the underlying physics. The Quantum Internet will operate according to unique physical principles such as quantum superposition, entanglement and teleportation [I-D.irtf-qirg-principles].

The Quantum Internet is not anticipated to replace the classical Internet. Instead the Quantum Internet will be integrated into 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.

2. Conventions used in this document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

3. Terms and Acronyms List

This document assumes that the reader is familiar with the quantum information technology related terms and concepts that are described in [I-D.irtf-qirg-principles]. In addition, the following terms and acronyms are defined here for clarity:

• Bit - Binary Digit (i.e., fundamental unit of information in a classical computer).
• 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.
• Hybrid Internet - The "new" or evolved Internet to be formed due to a merger of the classical Internet and the Quantum Internet.
• Noisy Intermediate-Scale Quantum (NISQ) - NISQ was defined in [Preskill] 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 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.
• 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 the Quantum Internet it must be able to generate/transmit and/or receive/process qubits. A quantum end-node, if it has quantum memory and quantum computing capabilities, can be regarded as a quantum computer. 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 Internet - 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 Internet will be merged into the classical Internet to form a new hybrid Internet. The Quantum Internet will use both quantum channels, and classical channels provided by the classical Internet. The Quantum Internet may either improve classical applications or may enable new quantum applications.
• Quantum Computer (QC) - Compared to a quantum end-node, a QC has more capabilities such as quantum memory and quantum circuits, which are required for performing quantum computing tasks.
• Qubit - Quantum Bit (i.e., fundamental unit of information in a quantum computer). 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 |0> or |1>. However, the qubit is different than a classic bit in that the qubit is in a linear combination of both states before it is measured and termed to be in superposition. A photon or an electron can be used to represent a qubit.

4. Quantum Internet Applications

4.1. Overview

The Quantum Internet is expected to be extremely beneficial for a subset of existing and new applications. We use "applications" in the widest sense of the word and include functionality typically contained in Layers 4 (Transport) to Layers 7 (Application) of the Open System Interconnect (OSI) model.

The expected applications using Quantum Internet are still being developed as we are in the formative stages of the Quantum Internet [Castelvecchi] [Wehner]. However, an initial (and non-exhaustive) list of the applications to be supported on the Quantum Internet can be identified and classified using different schemes. We concentrate on the telecom centric classification of control plane versus data plane. We also briefly discuss other possible classification schemes.

4.2. Control vs Data Plane Classification

Traditionally, in the Internet most applications are classified as either control plane functionality or data plane functionality. Similarly, we classify Quantum Internet applications using the paradigm of control plane applications versus data plane applications 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).
• 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.

Some examples of classic Internet control plane applications are Domain Name Server (DNS), Session Information Protocol (SIP), and Internet Control Message Protocol (ICMP). Furthermore, examples of classic Internet 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.

4.2.1. Control Plane Applications

Control Plane Applications using Quantum Internet:

1. 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) [Renner].
2. Fast Byzantine negotiation - Refers to a quantum network based method for fast agreement in Byzantine negotiations [Fitzi]. This can be used for the popular financial blockchain feature as well as other distributed computing features which use Byzantine negotiations.
3. Network clock synchronization - Refers to a world wide set of atomic clocks connected by the Quantum Internet to achieve an ultra precise clock signal [Komar].
4. Position verification - Refers to a method for an end-node to prove that it is at a particular location to, for example, access a specific service [Unruh].

4.2.2. Data Plane Applications

Data Plane Applications using Quantum Internet:

1. Distributed quantum computing - Refers to a collection of remote small capacity quantum computers (i.e., each supporting a few qubits) that are connected and working together in a coordinated fashion so as to simulate a virtual large capacity quantum computer [Wehner].
2. 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 [Fitzsimons].

4.3. Other Possible Classifications

Applications may also be classified by the industry sector that they serve. For example, applications may be classified as:

• Quantum computing (e.g., distributed quantum computing)
• Quantum cryptography (e.g., QKD)
• Quantum metrology (e.g., detection of gravitational radiation by measurement on two widely separated masses)
• Quantum Internet of Things (IoT)

This is a valid and useful classification scheme. However, since the classic Internet community is used to the control plane versus data plane paradigm we will primarily use that approach in this document.

5. Selected Quantum Internet Use Cases

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.

5.1. Secure Communication Setup

In this scenario, two banks (i.e., Bank #1 and Bank #2) need to have secure communications for transmitting important financial transaction records (see Figure 1). 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 send a classic secret key to 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 could 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 Figure 1 is an example.

One requirement for this secure communication setup process is that it should not be vulnerable to any classic or quantum computing attack. This can be realized using QKD [ETSI-QKD-Interfaces]. QKD can securely distribute a secret key between two quantum nodes, without physically transmitting it through the network and thus achieving the required security. 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 have been described in ETSI GS QKD 002 [ETSI-QKD-UseCases].

In general, QKD (e.g., [BB84]) without using entanglement works as follows:

1. The source quantum node A (e.g. Alice) transforms the secret key to qubits. Basically, for each classical bit in the secret key, the source quantum node A randomly selects one quantum computational basis and uses it to prepare/generate a qubit for the classical bit.
2. The source quantum node A sends qubits to the destination quantum node B (e.g. Bob) via quantum channel.
3. The destination quantum node receives qubits and measures them based on its random quantum basis.
4. The destination quantum node sends the measurement results (i.e., classic bits) to the source quantum node via any public classic channel.
5. Both the source node and the destination node inform each other’s random quantum basis.
6. Both nodes discard any measurement bit under different quantum basis and store all remaining bits as the secret key.

It is worth noting that:

1. There are some entanglement-based QKD protocols such as [Treiber], which work differently than above steps. The entanglement-based schemes, where entangled states are prepared externally to Alice and Bob, are not normally considered "prepare-and-measure" as defined in [Wehner]; other entanglement-based schemes, where entanglement is generated within Alice 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 Alice before being sent to Bob for measurement.
2. There are many enhanced QKD protocols based on [BB84]. 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 [ZhangPeiyu]. These enhanced QKD protocol can work differently than the steps of BB84 protocol [BB84].
3. 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 [QinHao]. One or multiple trusted QKD relays [ZhangQiang] 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.

As a result, the Quantum Internet in Figure 1 contains quantum channels. And in order to support secure communication setup especially in large-scale deployment, it also requires entanglement generation and entanglement distribution [I-D.van-meter-qirg-quantum-connection-setup], quantum repeaters/routers, and/or trusted QKD relays.

  
    
+---------------+
|   End User    |
|(e.g., Banking |
|  Application) |
+---------------+
      ^
      | User Interface
      | (e.g., GUI)    
      V                
+-----------------+     /--------\     +-----------------+         
|                 |--->( Quantum  )--->|                 |
|     Source      |    ( Internet )    |  Destination    |
|     Quantum     |     \--------/     |    Quantum      |
|     Node A      |                    |     Node B      |
| (e.g., Bank #1) |     /--------\     | (e.g., Bank #2) |
|                 |    ( Classical)    |                 |                            
|                 |<-->( Internet )<-->|                 |
+-----------------+     \--------/     +-----------------+
                     
				

Figure 1: Secure Communication Setup

5.2. Distributed Quantum Computing

In this scenario, Noisy Intermediate-Scale Quantum (NISQ) computers distributed in different locations are available for sharing. According to the definition in [Preskill], 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 [Caleffi] [Cacciapuoti01] [Cacciapuoti02]. 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.

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 Figure 2). In this case, qubits will be transmitted among connected quantum computers via quantum channels, while classic control messages will be transmitted among them via classic channels for coordination and control purpose . Qubits from one NISQ computer to another NISQ computer are very sensitive and cannot 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 Figure 2 does not cover measurement-based distributed quantum computing, where quantum teleportation may not be required.

Specifically, the following steps happen between A and B:

1. The quantum computer A locally generates some sensitive data qubits to be teleported to the quantum computer B.
2. 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).
3. Then, the quantum computer A performs a Bell measurement of the entangled qubit |q1> and the sensitive data qubit.
4. The result from this Bell measurement will be encoded in two classic bits, which will be physically transmitted via a classic channel to the quantum computer B.
5. Based on the received two classic 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 Figure 2, the Quantum Internet contains quantum channels and quantum repeaters/routers [I-D.irtf-qirg-principles]. This use case needs to support entanglement generation in order to enable quantum teleportation, entanglement distribution or quantum connection setup [I-D.van-meter-qirg-quantum-connection-setup] in order to support long-distance quantum teleportation.

  
    
                  +-----------------+
                  |     End-User    |
                  |(e.g., Scientist)|
                  +-----------------+
                           ^
                           |User Interface (e.g. GUI)
                           |
        +------------------+-------------------+
        |                                      |
        |                                      |
        V                                      V              
+----------------+     /--------\     +----------------+         
|                |--->( Quantum  )--->|                |
|                |    ( Internet )    |                |
|   Quantum      |     \--------/     |   Quantum      |
|   Computer A   |                    |   Computer B   |
| (e.g., Site #1)|     /--------\     | (e.g., Site #2)|
|                |    ( Classical)    |                |                            
|                |<-->( Internet )<-->|                |
+----------------+     \--------/     +----------------+                            
                     
				

Figure 2: Distributed Quantum Computing

5.3. Secure Quantum Computing with Privacy Preservation

Secure computation with privacy preservation refers to the scenario:

1. A client node with source data delegates the computation of the source data to a remote computation node.
2. Furthermore, the client node does not want to disclose any source data to the remote computation node and thus preserve the source data privacy.
3. 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 Figure 3, the client node could be a virtual voice-controlled home assistant device like Amazon's Alexa product. The remote computation node could be a quantum computer in the cloud. A resident as an end-user uses voice to control the home device. The home device captures voice-based commands from the end-user. Then, the home device interfaces to a home quantum terminal node (e.g., a home gateway), which interacts with the remote computation node to perform computation over the captured voice-based commands. The home quantum terminal could be either a bare-bone quantum end-node or a full-fledged quantum computer.

In this particular case, there is no privacy concern since the source data (i.e., captured voice-based commands) will not be sent to the remote computation node which could be compromised. Protocols [Fitzsimons] for delegated quantum computing or blind quantum computation can be leveraged to realize secure delegated computation and guarantee privacy preservation simultaneously. Using delegated quantum computing protocols, the client node does not need send the source data but qubits with some measurement instructions to the remote computation node (e.g., a quantum computer).

After receiving qubits and measurement instructions, the remote computation node performs the following actions:

1. It first performs certain quantum operations on received qubits and measure them according to received measurement instructions to generate computation results (in classic bits).
2. Then it sends the computation results back to the client node via classic channel.
3. In this process, the source data is not disclosed to the remote computation node and the privacy is preserved.

In Figure 3, the Quantum Internet contains quantum channels and quantum repeaters/routers for long-distance qubits transmission [I-D.irtf-qirg-principles].

  
    
+----------------+
|   End-User     |
|(e.g., Resident)|
+----------------+
        ^
        | User Interface
        | (e.g., voice commands)
        V
+----------------+
|   Home Device  |		
+----------------+
        ^
        | Classic 
        | Channel
        V
+----------------+     /--------\     +----------------+         
|                |--->( Quantum  )--->|                |
|   Quantum      |    ( Internet )    |   Remote       |
|   Terminal     |     \--------/     |   Computation  |
|   Node         |                    |   Node         |
|  (e.g., Home   |     /--------\     |   (e.g., QC    |
|   Gateway)     |    ( Classical)    |   in Cloud)    |                            
|                |<-->( Internet )<-->|                |
+----------------+     \--------/     +----------------+                            
                     
				

Figure 3: Secure Computation with Privacy Preservation

6. General Requirements

Based on the above applications and use cases, some general requirements on the Quantum Internet from the networking perspective are identified as follows:

1. 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.
2. Quantum repeaters/routers should support robust and efficient entanglement distribution.
3. 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 must be sent via classical channels.

7. Conclusion

This document provides an overview of some expected applications for the Quantum Internet and details selected use cases. The applications are classified as either control plane or data plane functionality as typical for Internet applications. One key take away is that a variety of control plane applications will run on the Quantum Internet. In contrast, the data plane applications running on the Quantum Internet will be focused on supporting different forms of remote quantum computing. This set of applications may, of course, naturally expand over time as the Quantum Internet matures.

This document can also serve as an introductory text to persons 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 specific Quantum Internet functionality required to implement the applications and uses cases described herein. To this end, a few key requirements for the Quantum Internet are specified.

8. IANA Considerations

This document requests no IANA actions.

9. Security Considerations

This document does not define an architecture nor a specific protocol for the Quantum Internet. It focuses on detailing use cases and describing typical Quantum Internet applications. However, some useful observations can be made regarding security as follows.

It has been clearly identified that once large-scale quantum computing becomes reality it will be able to theoretically break many of the public-key (i.e., asymmetric) cryptosystems currently in use because of the exponential increase of computing power with quantum computing. This would negatively affect many of the security mechanisms currently in use on the classic Internet. This has given strong impetus for starting development of new cryptographic systems that are secure against quantum computing attacks [NISTIR8240].

Paradoxically, development of a Quantum Internet will also mitigate the threats posed by quantum computing attacks against public-key cryptosystems. Specifically, the secure communication setup feature of the Quantum Internet as described in Section 5.1 will be strongly resistant to both classical and quantum computing attacks.

Finally, Section 5.3 provides a method to perform remote quantum computing while preserving the privacy of the source data.

10. Acknowledgments

The authors want to thank Xavier de Foy, Patrick Gelard, and Wojciech Kozlowski for their very useful reviews and comments to the document.

11. Informative References

Authors' Addresses