wdiff rfc9583v1.txt rfc9583.txt

Internet Research Task Force (IRTF) C. Wang
Request for Comments: 9583 InterDigital Communications, LLC
Category: Informational A. Rahman
ISSN: 2070-1721 Ericsson
R. Li
Kanazawa University
M. Aelmans
Juniper Networks
K. Chakraborty
The University of Edinburgh
May
June 2024

Application Scenarios for the Quantum Internet

Abstract

The Quantum Internet has the potential to improve application
functionality by incorporating quantum information technology into
the infrastructure of the overall Internet. This document provides
an overview of some applications expected to be used on the Quantum
Internet and categorizes them. Some general requirements for the
Quantum Internet are also discussed. The intent of this document is
to describe a framework for applications and to describe a few
selected application scenarios for the Quantum Internet. This
document is a product of the Quantum Internet Research Group (QIRG).

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for informational purposes.

This document is a product of the Internet Research Task Force
(IRTF). The IRTF publishes the results of Internet-related research
and development activities. These results might not be suitable for
deployment. This RFC represents the consensus of the QIRG Research
Group of the Internet Research Task Force (IRTF). Documents approved
for publication by the IRSG are not candidates for any level of
Internet Standard; see Section 2 of RFC 7841.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9583.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.

Table of Contents

1. Introduction
2. Terms and Acronyms List
3. Quantum Internet Applications
3.1. Quantum Cryptography Applications
3.2. Quantum Sensing/Metrology Sensing and Metrology Applications
3.3. Quantum Computing Applications
4. Selected Quantum Internet Application Scenarios
4.1. Secure Communication Setup
4.2. Blind Quantum Computing
4.3. Distributed Quantum Computing
5. General Requirements
5.1. Operations on Entangled Qubits
5.2. Entanglement Distribution
5.3. The Need for Classical Channels
5.4. Quantum Internet Management
6. Conclusion
7. IANA Considerations
8. Security Considerations
9. Informative References
Acknowledgments
Authors' Addresses

1. Introduction

The Classical, i.e., non-quantum, Internet has been constantly
growing since it first became commercially popular in the early
1990s. It essentially consists of a large number of end nodes (e.g.,
laptops, smart phones, and 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., fiber optics, Wi-Fi, cellular
wireless, and 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 [Wehner]. End nodes will also be a
part of the Quantum Internet; in that case, they are called "quantum
end nodes" and may be connected by quantum repeaters/routers. repeaters and/or routers.
These quantum end nodes will also run value-added applications, which
will be discussed later.

The physical layer quantum channels between the various nodes in the
Quantum Internet can be either waveguides, such as optical fibers, or
free space. Photonic channels are particularly useful because light
(photons) is very suitable for physically realizing qubits. The
Quantum Internet will operate according to quantum physical
principles such as quantum superposition and entanglement [RFC9340].

The Quantum Internet is not anticipated to replace but rather to
enhance the Classical Internet and/or provide breakthrough
applications. For instance, quantum key distribution Quantum Key Distribution can improve the
security of the Classical Internet, and quantum computing can
expedite and optimize computation-intensive tasks in the Classical
Internet. The Quantum Internet will run in conjunction with the
Classical Internet. The process of integrating the Quantum Internet
with the Classical Internet is similar to the process of introducing
any new communication and networking paradigm into the existing
Internet but with more profound implications.

The intent of this document is to provide a common understanding and
framework of applications and application scenarios for the Quantum
Internet. It is noted that ITU-T SG13-TD158/WP3 [ITUT] briefly
describes four kinds of use cases of quantum networks beyond quantum
key distribution Quantum
Key Distribution networks: quantum time synchronization use cases,
quantum computing use cases, quantum random number generator use
cases, and quantum communication use cases (e.g., quantum digital
signatures, quantum anonymous transmission, and quantum money). This
document focuses on quantum applications that have more impact on
networking, such as secure communication setup, blind quantum
computing, and distributed quantum computing; although these
applications were mentioned in [ITUT], this document gives more
details and derives some requirements from a networking perspective.

This document was produced by the Quantum Internet Research Group
(QIRG). It was discussed on the QIRG mailing list and during several
meetings of the research group. It has been reviewed extensively by
the QIRG members with expertise in both quantum physics and Classical
Internet operation. This document represents the consensus of the
QIRG members, of both experts in the subject matter (from the quantum
and networking domains) and newcomers, who are the target audience.
It is not an IETF product and is not a standard.

2. Terms and Acronyms List

This document assumes that the reader is familiar with the quantum
information technology related terms and
concepts that are relate to quantum information technology described in
[RFC9340]. In addition, the following terms and acronyms are defined
herein for clarity:

Bell Pairs: A special type of two-qubits quantum state. state that is two qubits. The
two qubits show a correlation that cannot be observed in classical
information theory. We refer to such correlation as quantum
entanglement. Bell pairs exhibit the maximal quantum
entanglement. One example of a Bell pair is
(|00>+|11>)/(Sqrt(2)). The Bell pairs are a fundamental resource
for quantum communication.

Bit: Binary digit (i.e., fundamental unit of information in
classical communications and classical computing). Bit is used in
the Classical Internet where the state of a bit is deterministic.
In contrast, qubit is used in the Quantum Internet where the state
of a qubit is uncertain before it is measured.

Classical Internet: The existing, deployed Internet (circa 2020)
where bits are transmitted in packets between nodes to convey
information. The Classical Internet supports applications that
may be enhanced by the Quantum Internet. For example, the end-to-
end security of a Classical Internet application may be improved
by a secure communication setup using a quantum application.
Classical Internet is a network of classical network nodes that do
not support quantum information technology. In contrast, Quantum
Internet consists of quantum nodes based on quantum information
technology.

Entanglement Swapping: It is a process of sharing an entanglement
between two distant parties via some intermediate nodes. For
example, suppose that there are three parties (A, B, and C) and
that each of the parties (A, B) and (B, C) share Bell pairs. B
can use the qubits it shares with A and C to perform entanglement-
swapping operations, and as a result, A and C share Bell pairs.
Entanglement swapping essentially realizes entanglement
distribution (i.e., two nodes separated in distance can share a
Bell pair).

Fast Byzantine Negotiation: A Quantum-based quantum-based method for fast
agreement in Byzantine negotiations [Ben-Or] [Taherkhani].

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
[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 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: A self-identified message with in-band addresses or other
information that can be used for forwarding the message. The
message contains an ordered set of bits of determinate number.
The bits contained in a packet are 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 [BB84] is a
prepare-and-measure quantum key distribution protocol.

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 End Node: An end node that 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. A quantum end node must also be able to interface to
the Classical Internet for control purposes and thus be able to
receive, process, and transmit classical bits/packets. bits and/or packets.

Quantum Internet: A network of Quantum Networks. quantum networks. The Quantum
Internet is expected to be merged into the Classical Internet.
The Quantum Internet may either improve classical applications or
enable new quantum applications.

Quantum Key Distribution (QKD): A method that leverages quantum
mechanics such as a no-cloning theorem to let two parties create
the same arbitrary classical key.

Quantum Network: A new type of network enabled by quantum
information technology where quantum resources, such as qubits and
entanglement, are transferred and utilized between quantum nodes.
The Quantum Network quantum network will use both quantum channels and classical
channels provided by the Classical Internet, referred to as a
"hybrid implementation".

Quantum Teleportation: A technique for transferring quantum
information via Local Operations and Classical Communication
(LOCC). If two parties share a Bell pair, then by using quantum
teleportation, a sender can transfer a quantum data bit to a
receiver without sending it physically via a quantum channel.

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 denotes its basis state vector as |0> or |1> using
Dirac's ket notation. 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. Any of several Degrees of Freedom (DOF) of a
photon (e.g., polarization, time bib, and/or frequency) or an
electron (e.g., spin) can be used to encode a qubit.

Teleport a Qubit: An operation on two or more carriers in succession
to move a qubit from a sender to a receiver using quantum
teleportation.

Transfer a Qubit: An operation to move a qubit from a sender to a
receiver without specifying the means of moving the qubit, which
could be "transmit" or "teleport".

Transmit a Qubit: An operation to encode a qubit into a mobile
carrier (i.e., typically photon) and pass it through a quantum
channel from a sender (a transmitter) to a receiver.

3. Quantum Internet Applications

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 [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 two
different schemes. Note that this document does not include quantum
computing applications that are purely local to a given node.

Applications may be grouped by the usage that they serve.
Specifically, applications may be grouped according to the following
categories:

Quantum cryptography applications: Refer to the use of quantum
information technology for cryptographic tasks (e.g., quantum key
distribution Quantum Key
Distribution [Renner]).

Quantum sensor applications: Refer to the use of quantum information
technology for supporting distributed sensors (e.g., clock
synchronization [Jozsa2000] [Komar] [Guo]).

Quantum computing applications: Refer to the use of quantum
information technology for supporting remote quantum computing
facilities (e.g., distributed quantum computing [Denchev]).

This scheme can be easily understood by both a technical and non-
technical audience. The next sections describe the scheme in more
detail.

3.1. Quantum Cryptography Applications

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)"
[Renner].

Fast Byzantine negotiation: Refers to a Quantum-based quantum-based method for
fast agreement in Byzantine negotiations [Ben-Or], for example, to
reduce the number of expected communication rounds and, in turn,
to achieve faster agreement, in contrast to classical Byzantine
negotiations. A quantum-aided Byzantine agreement on quantum
repeater networks as proposed in [Taherkhani] includes
optimization techniques to greatly reduce the quantum circuit
depth and the number of qubits in each node. Quantum-based
methods for fast agreement in Byzantine negotiations can be used
for improving consensus protocols such as practical Byzantine
Fault Tolerance (pBFT) as well as other distributed computing
features that use Byzantine negotiations.

Quantum money: Refers to the main security requirement of money is
unforgeability. A quantum money scheme aims to fulfill by
exploiting exploit the no-cloning no-
cloning property of the unknown quantum states. Though the
original idea of quantum money dates back to 1970, these early
protocols allow only the issuing bank to verify a quantum
banknote. However, the recent protocols such as public key
quantum money [Zhandry] allow anyone to verify the banknotes
locally.

3.2. Quantum Sensing/Metrology Sensing and Metrology Applications

The entanglement, superposition, interference, and squeezing of
properties can enhance the sensitivity of the quantum sensors and
eventually can outperform the classical strategies. 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, multiparameter estimation [Proctor].

Network clock synchronization: Refers to a world wide set of high-
precision clocks connected by the Quantum Internet to achieve an
ultra precise clock signal [Komar] 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, [Guo] uses an entangled quantum
network for measuring the average phase shift among multiple
distributed nodes.

Interferometric telescopes using quantum information: Refers to inte
rferometric techniques that are used to combine signals from two
or more telescopes to obtain measurements with higher resolution
than what could be obtained with either telescope individually.
It can make measurements of very small astronomical objects if the
telescopes are spread out over a wide area. However, the phase
fluctuations and photon loss introduced by the communication
channel between the telescopes put a limitation on the baseline
lengths of the optical interferometers. This limitation can
potentially be avoided using quantum teleportation. In general,
by sharing EPR-pairs Einstein-Podolsky-Rosen pairs using quantum repeaters,
the optical interferometers can communicate photons over long
distances, providing arbitrarily long baselines [Gottesman2012].

3.3. Quantum Computing Applications

In this section, we include the applications for the quantum
computing. It's anticipated that quantum computers as a cloud
service will become more available in future. Sometimes, to run such
applications in the cloud while preserving the privacy, a client and
a server need to exchange qubits (e.g., in blind quantum computation
[Fitzsimons] as described below). Therefore, such privacy preserving
quantum computing applications require a Quantum Internet to execute.

Examples of quantum computing include distributed quantum computing
and blind quantum computing, which can enable new types of cloud
computing.

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

Blind quantum computing: 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. Selected Quantum Internet Application Scenarios

The Quantum Internet will support a variety of applications and
deployment configurations. This section details a few key
application scenarios that illustrate the benefits of the Quantum
Internet. In system engineering, an application scenario 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.

4.1. Secure Communication Setup

In this scenario, two nodes (e.g., quantum node A and quantum node B)
need to have secure communications for transmitting confidential
information (see Figure 1). For this purpose, they first need to
securely share a classic secret cryptographic key (i.e., a sequence
of classical bits), which is triggered by an end user with local
secure interface to quantum node A. This results in a quantum node A
securely establishing a classical secret key with a quantum node B.
This is referred to as a "secure communication setup". Note that
quantum nodes A and B may be either a bare-bone quantum end node or a
full-fledged quantum computer. This application scenario shows that
the Quantum Internet can be leveraged to improve the security of
Classical Internet applications.

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 is unbreakable in
principle. QKD can securely establish a secret key between two
quantum nodes, using a classical authentication channel and insecure
quantum channel 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 side-
channel attacks that can compromise the system. An example of a
physical side-channel attack is 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 also use a classical authentication
channel and an insecure quantum channel such as the phase-remapping
attack, photon number splitting attack, and decoy state attack
[Zhao2018]. QKD can be used for many other cryptographic
communications, such as IPsec and Transport Layer Security (TLS),
where involved parties need to establish a shared security key,
although it usually introduces a high latency.

QKD is the most mature feature of quantum information technology and
has been commercially released in small-scale and short-distance
deployments. More QKD use cases are described in the ETSI document
[ETSI-QKD-UseCases]; in addition, interfaces between QKD users and
QKD devices are specified in the ETSI document [ETSI-QKD-Interfaces].

In general, the prepare-and-measure QKD protocols (e.g., [BB84])
without using entanglement work as follows:

1. The quantum node A encodes classical bits to qubits. Basically,
the node A generates two random classical bit strings X, X and Y.
Among them, it uses the bit string X to choose the basis and uses
Y to choose the state corresponding to the chosen basis. For
example, if X=0, then in case of the BB84 protocol, Alice
prepares the state in {|0>, |1>}-basis; otherwise, she prepares
the state in {|+>, |->}-basis. Similarly, if Y=0, then Alice
prepares the qubit as either |0> or |+> (depending on the value
of X); and if Y =1, then Alice prepares the qubit as either |1>
or |->.

2. The quantum node A sends qubits to the quantum node B via a
quantum channel.

3. The quantum node B receives qubits and measures each of them in
one of the two bases at random.

4. The quantum node B informs the quantum node A of its choice of
bases for each qubit.

5. The quantum node A informs the quantum node B which random
quantum basis is correct.

6. Both nodes discard any measurement bit under different quantum
bases, and the remaining bits could be used as the secret key.
Before generating the final secret key, there is a post-
processing procedure over authenticated classical channels. The
classical post-processing part can be subdivided into three
steps, namely parameter estimation, error correction, and privacy
amplification. In the parameter estimation phase, both Alice and
Bob use some of the bits to estimate the channel error. If it is
larger than some threshold value, they abort the protocol or
otherwise move to the error-correction phase. 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 entropic
uncertainty relation property theorem of quantum mechanics. As a
part of the post-processing procedure, both nodes usually also
perform information reconciliation [Elkouss] for efficient error
correction and/or conduct privacy amplification [Tang] for
generating the final information-theoretical secure keys.

7. The post-processing procedure needs to be performed over an
authenticated classical channel. In other words, the quantum
node A and the quantum node B need to authenticate the classical
channel to make sure there is no eavesdroppers or man-in-the-
middle on-path
attacks, according to certain authentication protocols such as
that described in [Kiktenko]. In [Kiktenko], the authenticity of
the classical channel is checked at the very end of the post-processing post-
processing procedure instead of doing it for each classical
message exchanged between the quantum node A and the quantum node
B.

It is worth noting that:

1. 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 concerning these attacks such as measurement-device-
independent
measurement-device-independent QKD [Zheng2019]. These enhanced
QKD protocols can work differently than the steps of BB84
protocol [BB84].

2. For large-scale QKD, QKD Networks (QKDNs) 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 [Qin]. One or multiple trusted QKD relays
[Zhang2018] may exist between the quantum node A and the 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 quantum repeaters and/or routers instead
of trusted QKD relays are needed for large-scale QKD.
Entanglement swapping can be leveraged to realize entanglement
distribution.

3. QKD provides an information-theoretical way to share secret keys
between two parties (i.e., a transmitter and a receiver) in the
presence of an eavesdropper. However, this is true in theory,
and there is a significant gap between theory and practice. By
exploiting the imperfection of the detectors, Eve can gain
information about the shared key [Xu]. To avoid such side-
channel attacks in [Lo], the researchers provide a QKD protocol
called "Measurement Device-Independent (MDI)" QKD that allows two
users (a transmitter "Alice" and a receiver "Bob") to communicate
with perfect security, even if the (measurement) hardware they
are using has been tampered with (e.g., by an eavesdropper) and
thus is not trusted. It is achieved by measuring correlations
between signals from Alice and Bob, rather than the actual
signals themselves.

4. QKD protocols based on Continuous Variable QKD (CV-QKD) have
recently seen plenty of interest as they only require
telecommunications equipment that is readily available and is
also in common use industry-wide. This kind of technology is a
potentially high-performance technique for secure key
distribution over limited distances. The recent demonstration of
CV-QKD shows compatibility with classical coherent detection
schemes that are widely used for high-bandwidth classical
communication systems [Grosshans]. Note that we still do not
have a quantum repeater for the continuous variable systems;
hence, these kinds of QKD technologies can be used for the short
distance communications or trusted relay-based QKD networks.

5. Secret sharing can be used to distribute a secret key among
multiple nodes by letting each node know a share or a part of the
secret key, while no single node can know the entire secret key.
The secret key can only be reconstructed via collaboration from a
sufficient number of nodes. Quantum Secret Sharing (QSS)
typically refers to the following scenario: the secret key to be
shared is based on quantum states instead of classical bits. QSS
enables splitting and sharing such quantum states among multiple
nodes.

6. There are some entanglement-based QKD protocols, such as that
described in [Treiber], [E91], and [BBM92], which work
differently than the above steps. The entanglement-based
schemes, where entangled states are prepared externally to the
quantum node A and the quantum node B, are not normally
considered "prepare and measure" as defined in [Wehner]. 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 quantum node A before being sent
to the quantum node B for measurement.

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 [QUANTUM-CONNECTION],
quantum repeaters/routers, repeaters and/or routers, and/or trusted QKD relays.

Figure 1: Secure Communication Setup

4.2. Blind Quantum Computing

Blind quantum computing refers to the following scenario:

1. A client node with source data delegates the computation of the
source data to a remote computation node (i.e., a server).

2. Furthermore, the client node does not want to disclose any source
data to the remote computation node, which preserves 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 2, a terminal node can be a small
quantum computer with limited computation capability compared to a
remote quantum computation node (e.g., a remote mainframe quantum
computer), but the terminal node needs to run a computation-intensive
task (e.g., Shor's factoring algorithm). The terminal node can
create individual qubits and send them to the remote quantum
computation node. Then, the remote quantum computation node can
entangle the qubits, calculate on them, measure them, generate
measurement results in classical bits, and return the measurement
results to the terminal node. It is noted that those measurement
results will look like purely random data to the remote quantum
computation node because the initial states of the qubits were chosen
in a cryptographically secure fashion.

As a new client/server client and server computation model, Blind Quantum
Computation (BQC) generally enables the following process:

1. The client delegates a computation function to the server.

2. The client does not send original qubits to the server but does
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 transforms
them to the final result qubits.

During this process, the server cannot figure out the original qubits
from the transformed qubits. Also, it will not take too much effort
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
that described in [Childs], 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 [Jozsa2005].

It is worth noting that:

1. The BQC protocol in [Childs] 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.

2. Universal BQC (UBQC) in [Broadbent] 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 that the quantum teleportation plus a rotated Bell
measurement realize 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
sends them to the server, and the server needs to first prepare
entangled states from all received qubits. Then, multiple
interaction and measurement rounds happen between the client and
the server. For each round, round:

i. the client computes and sends new measurement instructions
or measurement adaptations to the server;

ii. the server performs the measurement according to the
received measurement instructions to generate measurement
results (in qubits or classic bits); and

iii. then the client receives the measurement results and
transforms them to the final results.

3. A hybrid UBQC is proposed in [Zhang2009], where the server
performs both quantum circuits like that demonstrated in [Childs]
and quantum measurements like that demonstrated in [Broadbent] to
reduce the number of required entangled states in [Broadbent].
Also, the client is much simpler than the client in [Childs].
This hybrid BQC is a combination of a circuit-based BQC model and
a measurement-based BQC model.

4. It is ideal if the client in BQC is a purely classical client,
which only needs to interact with the server using classical
channels and communications. [Huang] demonstrates such an
approach where a classical client leverages two entangled servers
to perform BQC with the assumption that both servers cannot
communicate with each other; otherwise, the blindness or privacy
of the client cannot be guaranteed. The scenario as demonstrated
in [Huang] is essentially an example of BQC with multiple
servers.

5. 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". [Fitzsimons] discusses this
issue and compares it in various BQC protocols.

In Figure 2, the Quantum Internet contains quantum channels and
quantum repeaters/routers repeaters and/or routers for long-distance qubits
transmission [RFC9340].

Figure 2: Bind Quantum Computing

4.3. Distributed Quantum Computing

There can be two types of distributed quantum computing [Denchev]:

1. Leverage quantum mechanics to enhance classical distributed
computing. 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 [Pal].
Normally, pre-shared entanglement first needs to be established
among distributed parties, followed by LOCC operations at each
party. And it generally does not need to transfer qubits among
distributed parties.

2. 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. Entangled states will be needed and actually consumed
to support such distributed quantum computing tasks. It is worth
noting that:

a. Entangled states can be created beforehand and stored or
buffered;

b. The rate of entanglement creation will limit the performance
of practical Quantum Internet applications including
distributed quantum computing, although entangled states
could be buffered.

For example, [Gottesman1999] and [Eisert] have proved demonstrated that
a CNOT Controlled NOT (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 [Preskill], a NISQ computer can only realize a small
number of qubits and has limited quantum error correction. This
scenario is referred to as "distributed quantum computing" [Caleffi]
[Cacciapuoti2020] [Cacciapuoti2019]. This application scenario
reflects the vastly increased computing power that quantum computers
can bring as a part of the Quantum Internet, in contrast to classical
computers in the Classical Internet, in the context of a distributed
quantum computing ecosystem [Cuomo]. According to [Cuomo], quantum
teleportation enables a new communication paradigm, referred to as
"teledata" [VanMeter2006-01], 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" [VanMeter2006-02].

As an example, a user can leverage these connected NISQ computers to
solve highly complex scientific computation problems, such as
analysis of chemical interactions for medical drug development [Cao]
(see Figure 3). In this case, qubits will be transmitted among
connected quantum computers via quantum channels, while the user's
execution requests are transmitted to these quantum computers via
classical channels for coordination and control purpose. Another
example of distributed quantum computing is secure Multi-Party
Quantum Computation (MPQC) [Crepeau], which can be regarded as a
quantum version of classical secure Multi-Party Computation (MPC).
In a secure MPQC protocol, multiple participants jointly perform
quantum computation on a set of input quantum states, which are
prepared and provided by different participants. One of the primary
aims of the 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 [Lipinska].

For the example shown in Figure 3, we want to move qubits from one
NISQ computer to another NISQ computer. 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 3 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 [Chitambar] operations are conducted at the
quantum computers A and B in order to achieve quantum teleportation
as illustrated in Figure 3.

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). For example, the quantum computer
A can generate two entangled qubits (i.e., q1 and q2) and send q2
to the quantum computer B via quantum communications.

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
classical bits, which will be physically transmitted via a
classical channel to the quantum computer B.

5. 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 Figure 3, the Quantum Internet contains quantum channels and
quantum repeaters/routers repeaters and/or routers [RFC9340]. This application
scenario needs to support entanglement generation and entanglement
distribution (or quantum connection) setup [QUANTUM-CONNECTION] in
order to support quantum teleportation.

Figure 3: Distributed Quantum Computing

5. General Requirements

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 [Grumbling] for quantum computing.
Currently, a NISQ computer can achieve fifty to hundreds of qubits
with some given error rate.

On the network level, six stages of Quantum Internet development are
described in [Wehner] as a Quantum Internet technology roadmap as
follows:

1. Trusted repeater networks (Stage-1)

2. Prepare-and-measure networks (Stage-2)

3. Entanglement distribution networks (Stage-3)

4. Quantum memory networks (Stage-4)

5. Fault-tolerant few qubit networks (Stage-5)

6. Quantum computing networks (Stage-6)

The first stage is simple trusted repeater networks, while the final
stage is the 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.
Table 1 illustrates Quantum Internet application scenarios as
described in Sections 3 and 4 mapped to the Quantum Internet stages
described in [Wehner]. 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 the
trusted nodes.

* In Stage-2, the end users can prepare and measure the qubits. In
this stage, the users can verify classical passwords without
revealing them.

* 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, the quantum repeaters gain the capability of storing
and manipulating entangled qubits in the quantum memories. Using
these kinds of quantum networks, one can run sophisticated
applications like blind quantum computing, leader election, and
quantum secret sharing.

* In Stage-5, quantum repeaters can perform error correction; hence,
they can perform fault-tolerant quantum computations on the
received data. With the help of these repeaters, it is possible
to run distributed quantum computing and quantum sensor
applications over a smaller number of qubits.

* Finally, in Stage-6, distributed quantum computing relying on more
qubits can be supported.

Table 1: Example Application Scenarios in Different Quantum
Internet Stages

Some general and functional requirements on the Quantum Internet from
the networking perspective, based on the above application scenarios
and Quantum Internet technology roadmap [Wehner], are identified and
described in next sections.

5.1. Operations on Entangled Qubits

Methods for facilitating quantum applications to interact efficiently
with entangled 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 or entanglement distillation). Quantum nodes
may be quantum end nodes, quantum repeaters/routers, repeaters and/or routers, and/or
quantum computers.

5.2. Entanglement Distribution

Quantum repeaters/routers repeaters and/or routers should support robust and efficient
entanglement distribution in order to extend and establish a high-
fidelity 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 and then perform
entanglement-swapping operations at each of the intermediate nodes.

5.3. The Need for Classical Channels

Quantum end nodes must send additional information on classical
channels to aid in transferring and understanding qubits across
quantum repeaters/receivers. repeaters and/or receivers. Examples of such additional
information include qubit measurements in secure communication setup
(Section 4.1) and Bell measurements in distributed quantum computing
(Section 4.3). In addition, qubits are transferred individually and
do not have any associated packet header, which can help in
transferring the qubit. Any extra information to aid in routing,
identification, etc. of the qubit(s) must be sent via classical
channels.

5.4. Quantum Internet Management

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 the 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). A new management information model for the Quantum
Internet may need to be developed.

6. Conclusion

This document provides an overview of some expected application
categories for the Quantum Internet and then details selected
application scenarios. The applications are first grouped by their
usage, which is an easy-to-understand classification scheme. This
set of applications may, of course, 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 application scenarios
described herein.

7. IANA Considerations

This document has no IANA actions.

8. Security Considerations

This document does not define an architecture nor a specific protocol
for the Quantum Internet. It focuses instead on detailing
application scenarios and 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 [NISTIR8240] that, once large-scale quantum
computing becomes reality, 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
and optimizations). This would negatively affect many of the
security mechanisms currently in use on the Classical Internet that
are based on public key (Diffie-Hellman) (Diffie-Hellman (DH)) encryption. This has
given strong impetus for starting development of new cryptographic
systems that are secure against quantum computing attacks
[NISTIR8240].

Interestingly, development of the Quantum Internet will also mitigate
the threats posed by quantum computing attacks against Diffie-Hellman
based DH-based
public key cryptosystems. Specifically, the secure communication
setup feature of the Quantum Internet, as described in Section 4.1,
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
addressed in [RFC7258], 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, through traffic analysis, or by subverting the
cryptographic keys used to secure communications.

The secure communication setup feature of the Quantum Internet, as
described in Section 4.1, will be strongly resistant to pervasive
monitoring based on directly attacking (Diffie-Hellman) encryption
keys. Also, Section 4.2 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.

Modern networks are implemented with zero trust principles where
classical cryptography is used for confidentiality, integrity
protection, and authentication on many of the logical layers of the
network stack, often all the way from device to software in the cloud
[NISTSP800-207]. The cryptographic solutions in use today are based
on well-understood primitives, provably secure protocols, and state-
of-the-art implementations that are secure against a variety of side-
channel attacks.

In contrast to conventional cryptography and Post-Quantum
Cryptography (PQC), the security of QKD is inherently tied to the
physical layer, which makes the threat surfaces of QKD and
conventional cryptography quite different. QKD implementations have
already been subjected to publicized attacks [Zhao2008], and the
National Security Agency (NSA) notes that the risk profile of
conventional cryptography is better understood [NSA]. The fact that
conventional cryptography and PQC are implemented at a higher layer
than the physical one means PQC can be used to securely send
protected information through untrusted relays. This is in stark
contrast with QKD, which relies on hop-by-hop security between
intermediate trusted nodes. The PQC approach is better aligned with
the modern technology environment, in which more applications are
moving toward end-to-end security and zero-trust principles. It is
also important to note that, while PQC can be deployed as a software
update, QKD requires new hardware. In addition, the IETF has a
working group on Post-Quantum Use In Protocols (PQUIP) that is
studying PQC transition issues.

Regarding QKD implementation details, the NSA states that
communication needs and security requirements physically conflict in
QKD and that the engineering required to balance them has extremely
low tolerance for error. While conventional cryptography can be
implemented in hardware in some cases for performance or other
reasons, QKD is inherently tied to hardware. The NSA points out that
this makes QKD less flexible with regard to upgrades or security
patches. As QKD is fundamentally a point-to-point protocol, the NSA
also notes that QKD networks often require the use of trusted relays,
which increases the security risk from insider threats.

The UK's National Cyber Security Centre cautions against reliance on
QKD, especially in critical national infrastructure sectors, and
suggests that PQC, as standardized by NIST, is a better solution
[NCSC]. Meanwhile, the National Cybersecurity Agency of France has
decided that QKD could be considered as a defense-in-depth measure
complementing conventional cryptography, as long as the cost incurred
does not adversely affect the mitigation of current threats to IT
systems [ANNSI].

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Acknowledgments

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

Authors' Addresses

Chonggang Wang
InterDigital Communications, LLC
1001 E Hector St
Conshohocken, PA 19428
United States of America
Email: Chonggang.Wang@InterDigital.com

Akbar Rahman
Ericsson
349 Terry Fox Drive
Ottawa Ontario K2K 2V6
Canada
Email: Akbar.Rahman@Ericsson.Com

Ruidong Li
Kanazawa University
Kakumamachi, Kanazawa, Ishikawa
920-1192
Japan
Email: lrd@se.kanazawa-u.ac.jp

Melchior Aelmans
Juniper Networks
Boeing Avenue 240
1119 PZ Schiphol-Rijk
Netherlands
Email: maelmans@juniper.net

Kaushik Chakraborty
The University of Edinburgh
10 Crichton Street
Edinburgh, Scotland
EH8 9AB
United Kingdom
Email: kchakrab@exseed.edu.ac.uk kaushik.chakraborty9@gmail.com