RFC 9583

RFC 9583: Application Scenarios for the Quantum Internet 🦋

okay bestie, here's the vibe check. This is an IRTF doc, published June 2024, labelled Informational (not a standard, just vibes and research 🔬). It's written by C. Wang (InterDigital Communications, LLC), A. Rahman (Ericsson), R. Li (Kanazawa University), M. Aelmans (Juniper Networks), and K. Chakraborty (The University of Edinburgh). Its ISSN is 2070-1721. The title block doesn't list anything it obsoletes or updates, so it's a fresh start, no drama 💅.

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Abstract

okay so the Quantum Internet could level up apps by plugging quantum information tech into the infrastructure of the whole Internet 🌈. This doc is a little tour of some apps we expect to run on it, sorted into categories 🗂️. It also talks about some general requirements for the Quantum Internet. The goal is to lay out a framework for apps and walk through a few picked application scenarios ✨. This document is a product of the Quantum Internet Research Group (QIRG) 💜.

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Status of This Memo

not gonna lie, this part is kinda formal but it matters 🫶. This document is not an Internet Standards Track spec. It's just published for info purposes 📚.

This doc comes from the Internet Research Task Force (IRTF), which shares the results of Internet-related research and development 🔍. Those results might not be ready for deployment, so keep that in mind 🙈. This RFC reflects the consensus of the QIRG Research Group of the IRTF 👑. Anything the IRSG approves for publication is not eligible for any level of Internet Standard, see Section 2 of RFC 7841 💀.

If you want the latest on this doc's status, any errata, or how to send feedback, check https://www.rfc-editor.org/info/rfc9583 🎀.

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Copyright Notice

Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. ©️🌸

This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as they stand on the publication date. Read those carefully, because they spell out your rights and restrictions for this doc 📜.

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Table of Contents 🧚

   1.  Introduction
   2.  Terms and Acronyms List
   3.  Quantum Internet Applications
     3.1.  Quantum Cryptography Applications
     3.2.  Quantum 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

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1. Introduction 🌸

okay so the Classical Internet (aka the non-quantum one) has been growing nonstop since it got commercially popular in the early 1990s 📈. It's basically a huge pile of end nodes, like laptops, smartphones, and network servers, linked up by routers and grouped into Autonomous Systems 🖥️. Those end nodes run apps that deliver stuff like voice, video, or data to people 🎧. The links between nodes include backbone links (think fiber optics) and access links (fiber optics, Wi-Fi, cellular wireless, and Digital Subscriber Lines (DSLs)) 🛜. Bits travel across the Classical Internet inside packets 📦.

Research and experiments have been heating up over the last few years to build the Quantum Internet [Wehner] 🔥. End nodes will be part of it too, and in that case they're called "quantum end nodes" 🧪. They can be connected by quantum repeaters and/or routers, and they'll run value-added apps, which we'll get into later 💖.

The physical-layer quantum channels between nodes can be waveguides, like optical fibers, or free space 🌈. Photonic channels are especially cute because light (photons) is super good at physically representing qubits ✨. The Quantum Internet will run on quantum physics principles like quantum superposition and entanglement [RFC9340] 🦋.

The Quantum Internet isn't meant to replace the Classical Internet, it's meant to enhance it and/or unlock breakthrough apps 💅. For example, Quantum Key Distribution can make the Classical Internet more secure, and quantum computing can speed up and optimize computation-heavy tasks there 🔐. The two will run side by side 🫶. Plugging the Quantum Internet into the Classical one is similar to how any new communication and networking paradigm gets introduced to the existing Internet, just with way bigger implications 🤯.

The goal of this doc is to build a shared understanding and framework for Quantum Internet apps and application scenarios 🎀. Quick side note: ITU-T SG13-TD158/WP3 [ITUT] briefly covers four kinds of use cases for quantum networks beyond Quantum Key Distribution networks: quantum time synchronization, quantum computing, quantum random number generators, and quantum communication (like quantum digital signatures, quantum anonymous transmission, and quantum money) 💰. This doc zooms in on the apps that matter more for networking, like secure communication setup, blind quantum computing, and distributed quantum computing 🧠. Those were mentioned in [ITUT] too, but here we give more detail and pull out 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 research group meetings 🗣️. QIRG members with expertise in both quantum physics and Classical Internet operation reviewed it extensively 👩‍🔬. It reflects the consensus of QIRG members, including subject matter experts from both the quantum and networking domains and newcomers, who are the target audience 🌟. It is not an IETF product and it is not a standard, so no pressure 🙈💜.

2. Terms and Acronyms List 🎀

okay bestie, before we dive in you need the vocab 📚 this doc assumes you already know the quantum info tech stuff from [RFC9340]. but this RFC also defines a few extra terms "for clarity" so everyone's on the same page 💅

Bell Pairs: a special quantum state made of two qubits 🦋 the two qubits are correlated in a way classical information theory can't copy. we call that correlation quantum entanglement. Bell pairs show the maximal quantum entanglement, which is so iconic 😭 one example is (|00>+|11>)/(Sqrt(2)). they're a fundamental resource for quantum communication, so they're kinda the main character of this whole doc 👑

Bit: a binary digit, the basic unit of info in classical communications and classical computing 💜 bits are used on the Classical Internet, where a bit's state is deterministic. the qubit is the quantum version, used on the Quantum Internet, where a qubit's state is uncertain until you measure it 🌸

Classical Internet: the existing, deployed Internet (circa 2020) where bits get sent in packets between nodes to convey info 🌈 it supports apps that could get a glow-up from the Quantum Internet. like, the end-to-end security of a Classical Internet app could be improved by a secure setup done with a quantum app 🔐 it's a network of classical nodes that don't support quantum info tech. the Quantum Internet, on the other hand, is made of quantum nodes built on quantum info tech 🧚

Entanglement Swapping: a process for sharing entanglement between two distant parties through some middle nodes 🍓 imagine three parties, A, B, and C, where (A, B) and (B, C) each share Bell pairs. B can use the qubits it shares with A and C to do entanglement-swapping operations, and suddenly A and C share Bell pairs too 🤯 basically, entanglement swapping realizes entanglement distribution, meaning two nodes that are far apart can share a Bell pair ✨

Fast Byzantine Negotiation: a 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 each round they can (1) send any classical info to each other, (2) do local quantum operations on their own, and (3) make the actions in each round depend on results from earlier rounds. very organized, very bestie 📋

Noisy Intermediate-Scale Quantum (NISQ): NISQ was defined in [Preskill] to describe a near-term era in quantum tech 🌙 NISQ computers have two salient features. one, they have somewhere from 50 to a few hundred physical qubits (that's the intermediate-scale part). two, their qubits have inherent errors and imperfect control (that's the noisy part) 🙈

Packet: a self-identified message with in-band addresses or other info that can be used to forward it 📦 it holds an ordered set of bits of a determinate number, and the bits in a packet are classical bits 💅

Prepare and Measure: a set of Quantum Internet scenarios where quantum nodes only support simple quantum functionalities, meaning they can prepare qubits and measure qubits 🎀 for example, BB84 [BB84] is a prepare-and-measure quantum key distribution protocol. simple but iconic 🫧

Quantum Computer (QC): a quantum end node that also has quantum memory and quantum computing capabilities. that's a full-fledged quantum computer, period 👑

Quantum End Node: an end node that hosts user applications and interfaces with the rest of the Internet 💖 an end node can play a client, server, or peer-to-peer role as part of the app. a quantum end node also has to be able to interface with the Classical Internet for control purposes, so it's able to receive, process, and transmit classical bits and/or packets. it's a multitasker 💪

Quantum Internet: a network of quantum networks 🌌 it's expected to be merged into the Classical Internet, and it may either improve classical applications or enable brand-new quantum applications ✨

Quantum Key Distribution (QKD): a method that uses quantum mechanics, such as the no-cloning theorem, to let two parties create the same arbitrary classical key 🔑 it's giving secret-sharing energy 🤫

Quantum Network: a new type of network enabled by quantum info tech, where quantum resources like qubits and entanglement get transferred and used between quantum nodes 🦋 it uses both quantum channels and classical channels provided by the Classical Internet, which is called a "hybrid implementation" 🌸

Quantum Teleportation: a technique for transferring quantum info via Local Operations and Classical Communication (LOCC) 🪄 if two parties share a Bell pair, a sender can use quantum teleportation to transfer a quantum data bit to a receiver without physically sending it through a quantum channel. wild, right? 😭

Qubit: quantum bit, the basic unit of info in quantum communication and quantum computing 💜 it's similar to a classic bit in that its state is either "0" or "1" after it's measured, and its basis state vector is written as |0> or |1> using Dirac's ket notation 🌈 the difference is that a qubit can be in a linear combination of both states before it's measured. that's called superposition ✨ any of several Degrees of Freedom (DOF) of a photon (like polarization, time bib, and/or frequency) or an electron (like spin) can be used to encode a qubit 🧚

Teleport a Qubit: an operation on two or more carriers in succession that moves a qubit from a sender to a receiver using quantum teleportation 🫶

Transfer a Qubit: an operation that moves a qubit from a sender to a receiver without specifying how it moves, which could be "transmit" or "teleport" 🍓

Transmit a Qubit: an operation that encodes a qubit into a mobile carrier (typically a photon) and sends it through a quantum channel from a sender (a transmitter) to a receiver 🌙

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3. Quantum Internet Applications ✨

okay now the fun part 🎉 the Quantum Internet is expected to be beneficial for a subset of existing and new applications 💖 the apps are still being developed, since we're in the formative stages of the Quantum Internet [Castelvecchi] [Wehner]. still, there's an initial list (not exhaustive, so there's more out there 👀) of apps that will be supported, and they can be sorted using two different schemes. also, this document does not include quantum computing apps that are purely local to a given node 🙅‍♀️

apps can be grouped by the usage they serve. specifically, they can be grouped into these categories:

Quantum cryptography applications: the use of quantum info tech for cryptographic tasks, like Quantum Key Distribution [Renner] 🔐

Quantum sensor applications: the use of quantum info tech to support distributed sensors, like clock synchronization [Jozsa2000] [Komar] [Guo] ⏰

Quantum computing applications: the use of quantum info tech to support remote quantum computing facilities, like distributed quantum computing [Denchev] 🖥️

this scheme is easy to get for both technical and non-technical audiences 🫶 the next sections go deeper into it.

3.1. Quantum Cryptography Applications 🔐

examples of quantum cryptography apps include quantum-based secure communication setup and fast Byzantine negotiation 💜

Secure communication setup: secure cryptographic key distribution between two or more end nodes 🗝️ the most well-known method is called "Quantum Key Distribution (QKD)" [Renner] 💅

Fast Byzantine negotiation: a quantum-based method for fast agreement in Byzantine negotiations [Ben-Or] 🏃‍♀️ for example, it can reduce the number of expected communication rounds and therefore reach agreement faster, compared to classical Byzantine negotiations. a quantum-aided Byzantine agreement on quantum repeater networks, as proposed in [Taherkhani], includes optimization techniques that greatly reduce the quantum circuit depth and the number of qubits in each node 🧠 quantum-based methods for fast agreement can be used to improve consensus protocols like practical Byzantine Fault Tolerance (pBFT), plus other distributed computing features that use Byzantine negotiations 🌈

Quantum money: the main security requirement of money is unforgeability 💰 a quantum money scheme aims to exploit the no-cloning property of unknown quantum states 🫧 the original idea of quantum money dates back to 1970, but those early protocols only let the issuing bank verify a quantum banknote 😤 newer protocols, like public key quantum money [Zhandry], let anyone verify the banknotes locally. iconic glow-up ✨

3.2. Quantum Sensing and Metrology Applications 🔭

the entanglement, superposition, interference, and squeezing of properties can enhance the sensitivity of quantum sensors, and they can eventually outperform classical strategies 🚀 examples of quantum sensor apps include network clock synchronization, high-sensitivity sensing, and so on 🧚 these apps mainly use a network of entangled quantum sensors (aka quantum sensor networks) for high-precision, multiparameter estimation [Proctor] 💫

Network clock synchronization: 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: apps that use quantum phenomena to achieve reliable nanoscale sensing of physical magnitudes 🔬 for example, [Guo] uses an entangled quantum network to measure the average phase shift among multiple distributed nodes 🌸

Interferometric telescopes using quantum information: interferometric techniques that combine signals from two or more telescopes to get measurements with higher resolution than either telescope could get on its own 🌌 it can measure very small astronomical objects if the telescopes are spread out over a wide area 😍 but the phase fluctuations and photon loss introduced by the communication channel between the telescopes limit the baseline lengths of the optical interferometers 🥺 this limit can potentially be avoided using quantum teleportation. and in general, by sharing Einstein-Podolsky-Rosen pairs using quantum repeaters, optical interferometers can communicate photons over long distances, giving arbitrarily long baselines [Gottesman2012] 🔭🫶

3.3. Quantum Computing Applications ✨

okay so this is where the quantum computing stuff gets really spicy 🌶️💅 we're talking about applications for quantum computers! and bestie, it's anticipated that quantum computers as a cloud service will become more available in the future 🫶 like, you'll be able to rent time on one from the cloud, which is giving very main character energy 🌈

here's the thing though: sometimes you want to run an application in the cloud but you also want your privacy protected 🙈 so a client and a server might need to exchange qubits. the example given is blind quantum computation [Fitzsimons], which we'll get to below 💜 so basically, privacy-preserving quantum computing applications require a Quantum Internet to execute. no cap, the Quantum Internet is kind of non-negotiable here 😭🔥

examples of quantum computing that can enable brand new kinds of cloud computing include distributed quantum computing and blind quantum computing ✨ two icons, two vibes:

Distributed quantum computing: this one is so iconic 👑 it refers to a collection of small-capacity, remote quantum computers (so each one only supports a relatively small number of qubits) that are connected and work together in a coordinated fashion. the end goal? they simulate a virtual, large-capacity quantum computer 🧚 see [Wehner].

Blind quantum computing: this is the private, or blind, quantum computation era 🦋 it gives a client a way to delegate a computation task to one or more remote quantum computers without disclosing the source data to be computed. the client keeps its secrets, the cloud does the heavy lifting, and nobody's oversharing 🤫 see [Fitzsimons].

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4. Selected Quantum Internet Application Scenarios 🌸

okay now we're getting into the good stuff 💖 the Quantum Internet is going to support a whole variety of applications and deployment configurations, and this section walks through a few key application scenarios that show off its benefits 🎀

quick vibe check on the definition, because this matters 👀 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, all tied to a particular goal. that's the definition we're going to use in this section, so when you see "scenario" from here on, think of it like a little story with nodes, users, and a goal 🧚✨

4. Selected Quantum Internet Application Scenarios ✨

4.1. Secure Communication Setup 🔐

okay so bestie, this is the first scenario and it's giving "secure your whole vibe" 💖 Two nodes (like quantum node A and quantum node B) need to have secure communications so they can send confidential info (see Figure 1) 🎀. To do that, they first have to securely share a classic secret cryptographic key, which is just a sequence of classical bits 🧚. An end user with a local secure interface to quantum node A kicks this off, and then quantum node A securely sets up a classical secret key with quantum node B 🦋. The RFC calls this a "secure communication setup" ✨. Also, quantum nodes A and B can be a bare-bone quantum end node or a full-fledged quantum computer, either one is totally valid 💅. This scenario shows that the Quantum Internet can be used to level up the security of Classical Internet applications 👑.

So, one requirement here is that the setup should not be vulnerable to any classical or quantum computing attack 😭 This is where QKD comes in, and it's unbreakable in principle 🔥. QKD can securely establish a secret key between two quantum nodes by using a classical authentication channel and an insecure quantum channel, and it never physically sends the key through the network, which is how it gets the security it needs 💜. BUT, the QKD system has to be safe against physical side-channel attacks, because those can compromise it 💀. One example is secretly injecting extra light into the optical devices used in QKD to learn side info like the polarization 🙈. Other specialized physical attacks also use a classical authentication channel plus an insecure quantum channel, like the phase-remapping attack, the photon number splitting attack, and the decoy state attack [Zhao2018] 🌈. QKD can also be used for other crypto comms like IPsec and Transport Layer Security (TLS), where the parties need a shared security key, though it usually comes with high latency 🐢.

QKD is the most mature feature of quantum information tech 👑 and it's already been commercially released in small-scale, short-distance deployments ⭐. More QKD use cases are in the ETSI document [ETSI-QKD-UseCases], and the interfaces between QKD users and QKD devices are specified in the ETSI document [ETSI-QKD-Interfaces] 🍓.

In general, prepare-and-measure QKD protocols that don't use entanglement (e.g., [BB84]) go like this 🦋:

1. The quantum node A encodes classical bits into qubits 🎀. Basically, node A generates two random classical bit strings, X and Y. It uses X to pick the basis and Y to pick the state within that basis. For example, if X=0, then in the BB84 protocol Alice prepares the state in the {|0>, |1>}-basis; otherwise she prepares it in the {|+>, |->}-basis. Similarly, if Y=0, Alice prepares the qubit as either |0> or |+> (depending on X), and if Y=1, she prepares it as either |1> or |-> 💅.
2. The quantum node A sends qubits to the quantum node B over a quantum channel 🚀.
3. The quantum node B receives the qubits and measures each one in one of the two bases, picked at random 🎲.
4. The quantum node B tells quantum node A which basis it chose for each qubit 🗣️.
5. The quantum node A tells quantum node B which random quantum basis was correct ✅.
6. Both nodes throw out any measurement bits where the quantum bases were different, and the leftovers can be used as the secret key 🗑️. Before the final key is made, there's a post-processing step over authenticated classical channels 🧼. That has three parts: parameter estimation, error correction, and privacy amplification 🧩. In parameter estimation, Alice and Bob use some of the bits to estimate the channel error. If it's bigger than a threshold value, they abort the protocol; otherwise they move on to error correction 🚫. Basically, if an eavesdropper tries to intercept and read the qubits sent from node A to node B, they'll get caught because of the entropic uncertainty relation of quantum mechanics 🕵️‍♀️. As part of post-processing, both nodes usually also do information reconciliation [Elkouss] for efficient error correction and/or privacy amplification [Tang] to make the final information-theoretically secure keys 🔑.
7. Post-processing has to run over an authenticated classical channel 🛡️. So quantum node A and quantum node B need to authenticate the classical channel to make sure there are no eavesdroppers or on-path attacks, using authentication protocols like the one described in [Kiktenko] 🔍. In [Kiktenko], the classical channel's authenticity gets checked at the very end of post-processing, instead of checking every single classical message exchanged between node A and node B ⏰.

It's worth noting that 📝:

1. There are lots of enhanced QKD protocols based on [BB84] 🌸. For example, loopholes have been found because of imperfections in measurement devices, and there are solutions for these attacks like measurement-device-independent QKD [Zheng2019] 🧠. These enhanced protocols can work differently from the BB84 steps 🔄.
2. Large-scale QKD needs QKD Networks (QKDNs), which can be seen as a subset of a Quantum Internet 🌐. A QKDN may have a QKD application layer, a QKD network layer, and a QKD link layer [Qin] 🍰. One or more trusted QKD relays [Zhang2018] may sit between node A and node B, connected by a QKDN 🤝. Or, a QKDN may rely on entanglement distribution and entanglement-based QKD protocols, in which case quantum repeaters and/or routers are needed for large-scale QKD instead of trusted QKD relays 🧲. Entanglement swapping can be used to make entanglement distribution happen 🪄.
3. QKD gives an information-theoretical way to share secret keys between a transmitter and a receiver even when an eavesdropper is around 🙌. BUT this is true in theory, and there's a big gap between theory and practice 😬. By exploiting detector imperfections, Eve can learn info about the shared key [Xu] 👀. To avoid these side-channel attacks, [Lo] introduces a QKD protocol called "Measurement Device-Independent (MDI)" QKD, which lets two users (a transmitter "Alice" and a receiver "Bob") communicate with perfect security, even if their measurement hardware has been tampered with (e.g., by an eavesdropper) and so isn't trusted 🛠️. It works by measuring correlations between signals from Alice and Bob, rather than the signals themselves 🪞.
4. QKD protocols based on Continuous Variable QKD (CV-QKD) have been getting lots of attention lately, because they only need telecom equipment that's already available and widely used across the industry 📡. This is a potentially high-performance way to distribute keys securely over limited distances 🏃‍♀️. A recent CV-QKD demonstration showed it's compatible with classical coherent detection schemes that are widely used for high-bandwidth classical communication [Grosshans] 💫. Note that there's still no quantum repeater for continuous variable systems, so these QKD techs are best for short-distance comms or trusted relay-based QKD networks 🚧.
5. Secret sharing can distribute a secret key among multiple nodes, with each node knowing only a share or part of the key, while no single node can know the entire key 🧩. The key can only be rebuilt when enough nodes work together 🤝. Quantum Secret Sharing (QSS) usually refers to a scenario where the secret key is based on quantum states instead of classical bits 🌈. QSS lets those quantum states be split and shared among multiple nodes ✂️.
6. Some entanglement-based QKD protocols, like those in [Treiber], [E91], and [BBM92], work differently from the steps above 🦄. Entanglement-based schemes where the entangled states are prepared outside of node A and node B are usually not considered "prepare and measure" as defined in [Wehner] 🙅‍♀️. Other entanglement-based schemes, where entanglement is generated inside the source node, can still count as "prepare and measure" 💅. Send-and-return schemes can also be "prepare and measure" if the info the keys come from is prepared in node A before being sent to node B for measurement 📦.

So, the Quantum Internet in Figure 1 has quantum channels 💜. And to support secure communication setup, especially at large scale, it also needs entanglement generation and distribution [QUANTUM-CONNECTION], quantum repeaters and/or routers, and/or trusted QKD relays 🎀✨.

        +---------------+
        |   End User    |
        +---------------+
              ^
              | Local Secure Interface
              | (e.g., the same physical hardware
              |  or a local secure network)
              V
        +-----------------+     /--------\     +-----------------+
        |                 |--->( Quantum  )--->|                 |
        |                 |    ( Internet )    |                 |
        |     Quantum     |     \--------/     |    Quantum      |
        |     Node A      |                    |     Node B      |
        |                 |     /--------\     |                 |
        |                 |    ( Classical)    |                 |
        |                 |<-->( Internet )<-->|                 |
        +-----------------+     \--------/     +-----------------+

                    Figure 1: Secure Communication Setup

4.2. Blind Quantum Computing 🎀

okay so blind quantum computing is basically this 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 still 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 those results to the terminal node. ngl this is the best part: 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 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 to transform the temporary result qubits to the final result qubits. One of the very first BQC protocols, such as the one described in [Childs], follows this process 👑. The client does need some basic quantum features though, such as quantum memory, qubit preparation and measurement, and qubit transmission. Measurement-based quantum computation is out of the scope of this document, but 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 circuits 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 quantum teleportation plus a rotated Bell measurement realize a quantum computation, which can be repeated multiple times to realize a sequence of quantum computations. 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:
   • 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 the ones demonstrated in [Childs] and quantum measurements like the ones 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 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 across various BQC protocols 🔍.

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

        +----------------+     /--------\     +-------------------+
        |                |--->( Quantum  )--->|                   |
        |                |    ( Internet )    | Remote Quantum    |
        |  Terminal      |     \--------/     | Computation       |
        |  Node          |                    | Node              |
        |  (e.g., a small|     /--------\     | (e.g., a remote   |
        |  quantum       |    ( Classical)    | mainframe         |
        |  computer)     |<-->( Internet )<-->| quantum computer) |
        +----------------+     \--------/     +-------------------+

                      Figure 2: Bind Quantum Computing

4.3. Distributed Quantum Computing 🧚

Okay bestie, so there are two types of distributed quantum computing [Denchev] 💖

1. Use quantum mechanics to level up classical distributed computing ✨ For example, entangled quantum states can improve leader election in classical distributed computing. Each party (like a node or a device) just measures its entangled quantum states, and there are no classical communications among the distributed parties [Pal]. Normally, the pre-shared entanglement has to be set up among the distributed parties first, and then each party does LOCC operations. It generally doesn't need to transfer qubits between the distributed parties 🫶
2. Distribute quantum computing functions across distributed quantum computers 🔥 A quantum computing task or function (like quantum gates) gets split up and spread across multiple physically separate quantum computers. It may or may not need to transmit qubits (inputs or outputs) between those computers. Entangled states are needed and actually consumed to support these distributed tasks 💅 Worth noting:
   • 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, even though entangled states could be buffered.

For example, [Gottesman1999] and [Eisert] have demonstrated that a 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.

Now for the second type as a scenario 🌸 Noisy Intermediate-Scale Quantum (NISQ) computers 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 called "distributed quantum computing" [Caleffi] [Cacciapuoti2020] [Cacciapuoti2019]. It's giving "vastly increased computing power" 👑 The quantum computers that come with the Quantum Internet are a huge glow-up compared to classical computers in the Classical Internet, when you look at a distributed quantum computing ecosystem [Cuomo]. According to [Cuomo], quantum teleportation enables a new communication paradigm called "teledata" [VanMeter2006-01], which moves quantum states among qubits on distributed quantum computers. Distributed quantum computation also needs the ability to remotely perform quantum computation on qubits sitting on distributed quantum computers. That's enabled by a technique called "telegate" [VanMeter2006-02] 🦋

As an example, a user can use these connected NISQ computers to solve highly complex scientific computation problems, such as analyzing chemical interactions for medical drug development [Cao] (see Figure 3) 🧪 In this case, qubits get sent between connected quantum computers over quantum channels, while the user's execution requests go to these quantum computers over classical channels for coordination and control. Another example is secure Multi-Party Quantum Computation (MPQC) [Crepeau], which you can think of as the 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 goals of secure MPQC is to make sure each participant does not know the input quantum states provided by the other participants 🙈 Secure MPQC relies on verifiable quantum secret sharing [Lipinska].

For the example in Figure 3, we want to move qubits from one NISQ computer to another NISQ computer 🍓 Quantum teleportation can be used 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 used, these steps happen between A and B. Basically, LOCC [Chitambar] operations happen at quantum computers A and B so they can achieve quantum teleportation, as shown 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 set up between the quantum computer A and the quantum computer B (so there are two entangled qubits: q1 at A and q2 at B). For example, the quantum computer A can generate two entangled qubits (q1 and q2) and send q2 to the quantum computer B via quantum communications.
3. Then, the quantum computer A performs a Bell measurement on the entangled qubit q1 and the sensitive data qubit.
4. The result of this Bell measurement gets encoded in two classical bits, which are physically sent over a classical channel to the quantum computer B.
5. Based on the two classical bits it received, the quantum computer B modifies the state of the entangled qubit q2 so it becomes a new qubit identical to the sensitive data qubit at the quantum computer A 🥰

In Figure 3, the Quantum Internet includes quantum channels and quantum repeaters and/or routers [RFC9340]. This application scenario needs to support entanglement generation and entanglement distribution (or quantum connection) setup [QUANTUM-CONNECTION] so that quantum teleportation can happen 🌈

                        +-----------------+
                        |     End User    |
                        |                 |
                        +-----------------+
                                 ^
                                 | Local Secure Interface
                                 | (e.g., the same physical hardware
                                 | or a local secure network)
                                 |
              +------------------+-------------------+
              |                                      |
              |                                      |
              V                                      V
      +----------------+     /--------\     +----------------+
      |                |--->( Quantum  )--->|                |
      |                |    ( Internet )    |                |
      |   Quantum      |     \--------/     |   Quantum      |
      |   Computer A   |                    |   Computer B   |
      | (e.g., Site #1)|     /--------\     | (e.g., Site #2)|
      |                |    ( Classical)    |                |
      |                |<-->( Internet )<-->|                |
      +----------------+     \--------/     +----------------+

                  Figure 3: Distributed Quantum Computing

5. General Requirements ✨

Okay so quantum tech is literally evolving every single day 😭, which means it's hard to predict the timeline and future milestones of quantum technologies, as pointed out in [Grumbling] for quantum computing. Right now, a NISQ computer can achieve fifty to hundreds of qubits with some given error rate 🫶.

On the network level, [Wehner] lays out six stages of Quantum Internet development as a Quantum Internet technology roadmap, like this:

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 maps the Quantum Internet application scenarios from Sections 3 and 4 onto those stages from [Wehner]. For example, secure communication setup can be supported in Stage-1, Stage-2, or Stage-3, but with different QKD solutions. Here's the breakdown:

• 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. 🌟

    +================+==========================+=====================+
    | Quantum        | Example Quantum Internet | Characteristic      |
    | Internet Stage | Use Cases                |                     |
    +================+==========================+=====================+
    | Stage-1        | Secure communication     | Trusted nodes       |
    |                | setup using basic QKD    |                     |
    +----------------+--------------------------+---------------------+
    | Stage-2        | Secure communication     | Prepare-and-measure |
    |                | setup using the QKD with | capability          |
    |                | end-to-end security      |                     |
    +----------------+--------------------------+---------------------+
    | Stage-3        | Secure communication     | Entanglement        |
    |                | setup using              | distribution        |
    |                | entanglement-enabled QKD |                     |
    +----------------+--------------------------+---------------------+
    | Stage-4        | Blind quantum computing  | Quantum memory      |
    +----------------+--------------------------+---------------------+
    | Stage-5        | Higher-accuracy clock    | Fault tolerance     |
    |                | synchronization          |                     |
    +----------------+--------------------------+---------------------+
    | Stage-6        | Distributed quantum      | More qubits         |
    |                | computing                |                     |
    +----------------+--------------------------+---------------------+

        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 and/or routers, and/or quantum computers. 💖

5.2. Entanglement Distribution 🔗

Quantum 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 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 gives you 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 a super 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 for 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. Bestie, that's the vibe 💜

7. IANA Considerations 📋

This document has no IANA actions. 🌸

8. Security Considerations ✨

okay bestie, this section is where the whole vibe gets a little serious 🥺 but it's also where the Quantum Internet really shows off what it can do 💅

This document doesn't define an architecture or a specific protocol for the Quantum Internet 🎀 it's more about mapping out application scenarios, requirements, and typical Quantum Internet apps. still, there are some salient observations about security that are worth knowing, so here we go 🦋

It's been identified in [NISTIR8240] that once large-scale quantum computing becomes a reality, it'll be able to break a lot of the public key (a.k.a. asymmetric) cryptosystems we use right now 😭 that's because quantum computers get a huge boost in ability for certain kinds of problems (like prime factorization and optimizations). this would hurt lots of Classical Internet security mechanisms that rely on public key (Diffie-Hellman (DH)) encryption. that danger is a big reason people have started building new cryptographic systems that stay secure against quantum computing attacks [NISTIR8240] 🔥

the scary part is that a lot of today's security is built on these public key systems, so the switch to new cryptography matters a lot.

Interestingly, though, developing the Quantum Internet will also help with the threats quantum computing poses to DH-based public key cryptosystems 🌈 specifically, the secure communication setup feature from Section 4.1 is going to be strongly resistant to both classical and quantum computing attacks against Diffie-Hellman based public key cryptosystems 👑

A key extra threat consideration for the Quantum Internet is covered in [RFC7258], which warns about pervasive monitoring as a widespread attack on privacy 🙈 pervasive monitoring is defined as widespread, and usually covert, surveillance that gathers application content or protocol metadata (such as headers) in an intrusive way. it can happen through active or passive wiretaps, through traffic analysis, or by subverting the cryptographic keys used to secure communications 💀

The secure communication setup feature from Section 4.1 is going to be strongly resistant to pervasive monitoring that tries to directly attack (Diffie-Hellman) encryption keys 🧚 also, Section 4.2 describes a way to do remote quantum computing while keeping the source data private 🫶 and finally, the intrinsic property of qubits to decohere when they're observed, even covertly, will theoretically allow detection of unwanted monitoring in some future solutions ✨

Modern networks are built on zero trust principles, where classical cryptography handles confidentiality, integrity protection, and authentication on many of the logical layers of the network stack, often all the way from the device to software in the cloud [NISTSP800-207] 🍓 the cryptographic solutions used today rely 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 pretty different 🦋 QKD implementations have already been hit with publicized attacks [Zhao2008], and the National Security Agency (NSA) notes that the risk profile of conventional cryptography is better understood [NSA] 😭 conventional cryptography and PQC are implemented at a higher layer than the physical one, which means PQC can be used to securely send protected information through untrusted relays 🔥 that's in stark contrast with QKD, which relies on hop-by-hop security between intermediate trusted nodes 💅 the PQC approach fits the modern tech environment better, since more applications are moving toward end-to-end security and zero-trust principles 🌸 it's also worth knowing that while PQC can be deployed as a software update, QKD requires new hardware 🎀 and the IETF has a working group on Post-Quantum Use In Protocols (PQUIP) that's studying PQC transition issues 🫶

On the QKD implementation details: the NSA states that communication needs and security requirements physically conflict in QKD, and that the engineering needed to balance them has extremely low tolerance for error 🙈 while conventional cryptography can sometimes be implemented in hardware for performance or other reasons, QKD is inherently tied to hardware. the NSA points out that this makes QKD less flexible when it comes to upgrades or security patches 💀 and since QKD is fundamentally a point-to-point protocol, the NSA also notes that QKD networks often need trusted relays, which raises the security risk from insider threats 👑

The UK's National Cyber Security Centre cautions against relying 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 a defense-in-depth measure that complements conventional cryptography, as long as the cost doesn't adversely affect mitigating current threats to IT systems [ANNSI] ✨

---

9. Informative References 🧚

okay bestie, here are all the references this doc leans on, complete with the details so you can go find them yourself 📚🦋

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---

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Acknowledgments ✨

okay bestie, the authors wanna give a huge shoutout 🫶 to 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, and Brian Trammell 💜. They gave super useful reviews and comments on the document, and it literally wouldn't be this polished without them 💅. Also, the whole QIRG community gets a big group hug 🌈 for their reviews and comments too, no cap.

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Authors' Addresses 🦋

These are the people who wrote it, so here's where to find them 💖

Chonggang Wang 🎀

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

Akbar Rahman 🌸

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

Ruidong Li 🧚

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

Melchior Aelmans 🍓

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

Kaushik Chakraborty 👑

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