Quantum Internet: Challenges and opportunities Antônio J. G. Abelém1, Gayane Vardoyan2, and Don Towsley2 1-Universidade Federal do Pará - UFPA 2-University of Massachuse;s - UMass, Amherst Introduction and Overview Quantum Informa3on and Quantum Compung Quantum Communication and Quantum Outline Networks Current Scenario and Challenges Concluding Remarks 2 • The main motivation for a quantum Internet is to enable applications that are out of reach for the classical Internet. • Enhance Internet technology by quantum Introducon communication between any two points; • May operate in parallel to the classical internet • connecting quantum processors in order to achieve capabilities that are probably impossible by using only classical means. 3 RESEARCH ◥ transmitting qubits over long distances a truly REVIEW formidable endeavor. Because qubits cannot be copied or amplified, repetition or signal am- plification are ruled out as a means to overcome QUANTUM INFORMATION imperfections, and a radically new technological development—such as quantum repeaters—is needed in order to build a quantum internet Quantum internet: A vision (Figs. 2 and 3) (5). We are now at an exciting moment in time, akin to the eve of the classical internet. In late for the road ahead 1969, the first message was sent over the nas- cent four-node network that was then still re- 1* 1 1,2 Stephanie Wehner , David Elkouss , Ronald Hanson ferred to as the Advanced Research Projects Agency Network (ARPANET). Recent technolog- The internet a vast network that enables simultaneous long-range classical — ical progress (6–9)nowsuggeststhatwemaysee communication has had a revolutionary impact on our world. The vision of a quantum — the first small-scale implementations of quan- internet is to fundamentally enhance internet technology by enabling quantum tum networks within the next 5 years. communication between any two points on Earth. Such a quantum internet may operate in At first glance, realizing a quantum internet parallel to the internet that we have today and connect quantum processors in order to (Fig. 3) may seem even more difficult than build- achieve capabilities that are provably impossible by using only classical means. Here, we ing a large-scale quantum computer. After all, we propose stages of development toward a full-blown quantum internet and highlight might imagine that in full analogy to the clas- Downloaded from experimental and theoretical progress needed to attain them. sical internet, the ultimate version of a quantum internet consists of fully fledged quantum com- he purpose of a quantum internet is to include secure access to remote quantum com- puters that can exchange an essentially arbi- enable applications that are fundamen- puters (2), more accurate clock synchronization trary number of qubits. Thankfully, it turns out tally out of reach for the classical internet. (3), and scientific applications such as com- that many quantum network protocols do not A quantum internet could thereby supple- bining light from distant telescopes to improve require large quantum computers to be real- T ment the internet we have today by using observations (4). As the development of a quan- ized; a quantum device with a single qubit at http://science.sciencemag.org/ quantum communication, but some researchers tum internet progresses, other useful applica- the end point is already sufficient for many go further and believe all communication will tions will likely be discovered in the next decade. applications. What’s more, errors in quantum eventually be done over quantum channels (1). Central to all these applications is that a quan- internet protocols can often be dealt with by The best-known application of a quantum in- tum internet enables us to transmit quantum using classical rather than quantum error cor- ternet is quantum key distribution (QKD), which bits (qubits), which are fundamentally differ- rection, imposing fewer demands on the control enables two remote network nodes to establish ent from classical bits. Classical bits can take and quality of the qubits than is the case for a Applica-ons (why Quantum Networks?)an encryption key whose security relies only on only two values, 0 or 1, whereas qubits can be fully fledged quantum computer. The reason the laws of quantum mechanics. This is im- in a superposition of 0 and 1 at the same time. why quantum internet protocols can outperform possible with the classical internet. A quantum Importantly, qubits cannot be copied, and any classical communication with such relatively internet, however, has many other applications attempt to do so can be detected. It is this fea- modest resources is because their advantages (Fig. 1) that bring advantages that are unattain- ture that makes qubits naturally well suited for rely solely on inherently quantum properties on October 16, 2019 • able with a classical network. Such applications security applications but at the same time makes such as quantum entanglement, which can be The best-known application of a quantum Internet is Quantum Key exploited already with very few qubits. By con- Distribution (QKD); Why Quantum Interet? trast, a quantum computer must feature more Fig. 1. Applications of a quantum Source: Physics World qubits than can be simulated on a classical com- internet. One application of a quan- puter in order to offer a computational advantage. • Other applications include: tum internet is to allow secure Given the challenges posed by the development of cryptography,access security to remote quantum– quantum com- key aquantuminternet,itisusefultoreflectonwhat • Secure communication: puters in the cloud (2). Specifically, a capabilities are needed to achieve specific quan- distribution (QKD)simple quantum terminal capable of tum applications and what technology is required • Secure access to remote quantum computerspreparing (in and measuringthe cloud) only single to realize them. (distributed) qubitsquantum can use a quantumcomputing internet to – Shor’s Here, we propose stages of development • Distributed quantum computing access a remote quantum computer toward a full-blown quantum internet. These algorithm, …in such a way that the quantum stages are functionality driven: Central to their • Quantum computing clusters; computer can learn nothing about definition is not the difficulty of experimentally which computation it has performed. achieving them but rather the essential question • high resolutionAlmost sensing all other applications of a quantum internet can be understood from two special features of of what level of complexity is needed to actually Tasks that require coordination: quantum entanglement. First, if two qubits at different network nodes are entangled with each enable useful applications. Each stage is inter- • clock synchronization, leader election, achievingother, then such consensus entanglement enables about stronger data, than classical Source:to helpIQOQI, correlation H. Ritsch two and coordination. For esting in its own right and distinguished by a high-precisionexample, clock for any synchronization measurement on qubit 1, if we made the same measurement on qubit 2, then we specific quantum functionality that is sufficient online bridge players coordinate their actions.instantaneously obtain the same answer, even though that answer is random and was not to support a certain class of protocols. To illus- determined ahead of time. Very roughly, it is this feature that makes entanglement so well suited for trate this, for each stage we give examples of • Scientific applications tasks that require coordination. Examples include clock synchronization (3), leader election, and known application protocols in which a quantum Source: MIT Technology achieving consensus about data (53), or even usingSource: entanglement nature.com to help two online bridge players internet is already known to bring advantages. coordinate their actions (39). The second feature of quantum entanglement is that it cannot be • such as combining light from distant telescopes to improve observations. 1 shared. If two qubits are maximally entangled with each other, then it is impossible by the4 laws of QuTech, Delft University of Technology, Post Office Box 5046, 2600 GA Delft, Netherlands. 2Kavli Institute of quantum mechanics for a third qubit to be just as entangled with either of them. This makes Nanoscience, Delft University of Technology, Post Office Box entanglement inherently private, bringing great advantages to tasks that require security such as 5046, 2600 GA Delft, Netherlands. generating encryption keys (12) or secure identification (24, 25). *Corresponding author. Email: [email protected] Wehner et al., Science 362, eaam9288 (2018) 19 October 2018 1 of 9 QuantumElementary Information quantum and Quantum 101 Computing bit has only two values: 0,1 • physicallyQuantum bit: represented qubit by two state device • Classical bit has only two values: 0,1 • physically represented by two state device 5 Quantum Information and Quantum Computing Quantum bits • QuantumQuantumqubit -bits: two-state qubits bits quantum-mechanical system • The analogue of the classical bit is the quantum bit, or qubit for short. example: photon polarization • Likequbit a classical - two-state bit, a qubit quantum-mechanical has a state, system example: photon polarization HorizontallyHorizontally polarized polarized Vertically polarized 1 Vertically polarized0 |�|0⟩⟩ 1 |�|1⟩ 0 |�⟩ 0 |�⟩ 1 • But... 0 1 6 Quantum bits 13 1.2 Quantum bits The bit is the