7/31/20 Novel techniques for ground to space quantumRESEARCH channels ◥ transmitting qubits over long distances a truly REVIEW formidable endeavor. Because qubits cannot be copied or amplified, repetition or signalIQC am- @ 2019: plification are ruled out as a means to overcome31 faculty QUANTUM INFORMATION imperfections, and a radically new technological development—such as quantum repeaters157— isGrad students needed in order to build a quantum internet57 Postdoc Quantum internet: A vision (Figs. 2 and 3) (5). We are now at an exciting moment in1800+ time, publications akin to the eve of the classical internet. In late for the road ahead 1969, the first message was sent over the$600M+ nas- funding cent four-node network that was then13 still spin re- -offs 1* 1 1,2 Thomas Jennewein Stephanie Wehner , David Elkouss , Ronald Hanson ferred to as the Advanced Research Projects Institute for Quantum Computing & Department of PhysicsAgency Network (ARPANET). Recent technolog- The internet a vast network that enables simultaneous long-range classical — and Astronomy,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 quantumUniversity of Waterloo tum networks within the next 5 years. communication between any two points on Earth. Such a quantum internet may operate in [email protected] first glance, realizing a quantum internet parallel to the internet that we have today and connect quantum processors in order to 2020.07(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 Downloaded from might imagine that in full analogy to the clas- experimental and theoretical progress needed to attain them. sical internet, the ultimate version of a quantum internet consists of fully fledged quantum com- 1 he purpose of a quantum internet is to include secure access to remote quantum com- puters that can exchange an2 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- http://science.sciencemag.org/ 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 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 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 on December 11, 2018 (Fig. 1) that bring advantages that are unattain- ture that makes qubits naturally well suited for rely solely on inherently quantum properties able with a classical network. Such applications security applications but at the same time makes such as quantum entanglement, which can be Quantum Internet Quantum computing in the cloud: exploited already with very few qubits. By con-Quantum Key Distribution RESEARCH trast, a quantum computer must feature more Fig. 1. Applications of a quantum qubits than can be simulated on a classical com- internet. One application of a quan- puter in order to offer a computational advantage. ◥ tum internet is to allow secure liness and need for a unified frameworkGiven for the challenges posed by the development of REVIEW SUMMARY access to remote quantum com- quantum internet researchers. aquantuminternet,itisusefultoreflectonwhat puters in the cloud (2). Specifically, a capabilities are needed to achieve specific quan-Fixes the loophole of key distribution, where classical keys simple quantum terminal capable of ADVANCES: We define different stagestum of applications and what technology is requiredcould be copied or compromised during transport. QUANTUM INFORMATION preparing and measuring only single development toward a full-blown quantumto realize them. qubits can use a quantum internet to internet. We expect that this classificationHere, we propose stages of developmentOnly transmit single quanta of light per bit. access a remote quantum computer will be instrumental in guiding and assessingtoward a full-blown quantum internet. These experimental progress as well as stimulating Quantum internet:RESEARCHin such| A aREVIEW way vision that the quantum stages are functionality driven: Central to their computer can learn nothing about the development of new applications by provid-definition is not the difficulty of experimentally for the road aheadwhich computation it has performed. ing a common language and reference frameachieving them but rather the essential question Almost all other applications of a quantum internet can be understoodfor the different from two scientific special features and engineering of of what level of complexity is needed to actually Fig. 4. Stagesquantum of quantum entanglement. First, if two qubits at different networkdisciplines nodes are involved. entangled with each enable usefulto attackapplications. the protocol, Each stage and is inter- remains secure at any Stephanie Wehner*, Davidinternet Elkouss, development. Ronaldother, thenHanson suchA entanglement spe- enables stronger than classicalMore correlation advanced and stages coordination. are distinguished For byesting a in itspoint own rightin the and future, distinguished even if by such a a quantum com- cific implementationexample, for of any a measurement quan- on qubit 1, if we made the samelarger measurement amount of function on qubitality, 2, then thus wesupportingspecific quantumputer functionality becomes available that is sufficient later on. This is provably instantaneously obtain the same answer, even though that answer is random and was not to support a certain class of protocols. To illus- ◥ ever more sophisticated Science 362, 303tum (2018) internet may, like for a impossible when using classical communication. BACKGROUND: The internet has had adetermined rev- as secure ahead ofaccess time. to Very remote roughly, quantum it is this comput- feature thatON makes OUR entanglementWEBSITE application so well suited protocols. for trate For this, for each stage we give examples of Alice Bob classical network,tasks that be require optimized coordination. Examples include clock synchronization (3), leader election, and known applicationThe BB84 protocols QKD in which (11) protocol a quantum can be realized by olutionary impact on our world. The vision of ers in the cloud. Read the full article each stage, we describe a quantum internet is to providefor distance, fundamen-achieving functionality, consensusCentral orto about all these data applications (53), or even is the using ability entanglementat http://dx.doi. to help two onlinesome bridge of the players applicationinternet is alreadyusing only known single-qubit to bring advantages. preparations and measure- tally new internet technology by enablingcoordinateof theira quantum actions internet (39). The to second transmit feature quantum of quantumorg/10.1126/ entanglement is thatprotocols it cannot that be are already both. The term network 1 ments tolerating some amount of post-selection p Eve ? shared. If two qubits are maximally entangled with each other,science.aam9288 then it is impossible by the laws of QuTech, Delft University of Technology, Post Office Box L. O. Mailloux et. al. Journal of Cyber Security and Information quantum communicationcommonly between any refers two tobits a (qubits) situation that are fundamentally different known and that can5046, be 2600Downloaded from GA Delft, Netherlands. 2Kavli Institute of quantum mechanics for a third qubit to be just as entangled.................................................. with either of them. This makes (19). For known protocols in this stage, eT + eM ≤ Systems, 4, 2 – Basic Complexity points on Earth. Such a quantumthat goes internet beyond point-to-pointthan classical bits. Whereas classical