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INTERVIEW National Science Review
6: 374–376, 2019
doi: 10.1093/nsr/nwy102
Advance access publication 21 September 2018
Jian-Wei Pan: building the quantum internet
By Philip Ball
For many decades since its inception in the early twentieth century, quantum mechanics seemed to be an exotic and peculiarly non-intuitive
kind of physics that applied to maer at the smallest scales: the laws that govern atoms, photons and subatomic particles. All our engineering,
meanwhile, was dominated by the familiar rules of classical physics, in which objects have denite positions, trajectories and properties.
But, in the past several decades, scientists have started to harness quantum rules in practical technologies. In 1985, the physicist Richard
Feynman suggested that computers governed by quantum rules might be capable of computations beyond the means of classical ones like those
in use today. At much the same time, other researchers showed that information encoded in quantum states could be transmied between a
sender and receiver using a kind of encryption that could not be intercepted and read without that being detected. Quantum computers and
quantum cryptography have now become central components of a real-world quantum-information technology that may soon nd scientic,
industrial and social uses.
ese applications could be increasingly enabled by a global information network with quantum capability: a quantum internet. China
is at the foreont of that enterprise, and one of the scientic leaders in this eort is Jian-Wei Pan of the University of Science and Technology
of China in Hefei. Pan studied for his PhD with quantum-information pioneer Anton Zeilinger in Vienna before returning to China to
implement these nascent technologies. In 2012, he won the International Quantum Communication Award and, in 2017, he was included
in Nature’s annual list of the ‘ten people who maered in science’ over the past year. at July, he and his colleagues reported ‘quantum
teleportation’ of photons om a ground-based station to a satellite 1400 km away.
NSR recently interviewed Professor Pan about the current achievements and future prospects for quantum-information technologies.
NSR: e quantum internet is becoming a popular buzzword,
butwhatwillitmean?
Pan: As we know, the internet is a global system to transfer, pro-
cess and store classical information. e quantum internet is the
equivalent for quantum information. e rst practical task for
a quantum internet may be sharing secret keys globally with un-
conditional security [that is, they are absolutely tamper-proof].
Quantum bits (qubits) and quantum entanglement [the inter-
dependence of states of the qubits] will be the basic resources of
the quantum internet. Various quantum-information tasks can
be realized in this system, such as quantum teleportation of in-
formation between any nodes, distributed quantum computa-
tion and high-precision quantum metrology.
NSR: What are the underlying principles of quantum physics
that a quantum internet would use?
Pan: e fundamental principle that quantum-information the-
ory is built on is quantum superposition. Superposition allows a
qubit to represent not just the 0 and 1 of classical bits but also any
intermediate state. Classically, a bit is either in state 0 or 1. But
in the quantum world, a qubit can be in a superposition of 0+1,
or another dierent combination of 0 and 1, simultaneously. A
basic principle is that no single measurement is sucient to re-
veal all the information. is leads to the quantum non-cloning
theorem, which dictates that an unknown quantum state can-
not be copied precisely. When a quantum system consists of
two or more qubits, superposition becomes entanglement and
makes the state space grows exponentially large. e uncertainty
principle and the non-cloning principle are the cornerstones of
Jian-Wei Pan, professor of the University of Science and
Technology of China (Courtesy of Professor Pan).
quantum communication and quantum computation, as well as
of the quantum internet.
Quantum teleportation is a way to transfer an unknown
quantum state from one particle to another at a distant location,
without sending the original particle itself. Assume that a pair of
entangled particles, denoted a and b, are exchanged between lo-
cations A and B. en let’s say an unknown qubit c needs to be
transferred from A to B. To eect teleportation, at A we perform
a collective measurement on a and c, followed by a certain oper-
ation (depending on the result of that collective measurement)
on b. en the (unknown) information will be ‘destroyed’ in c
and ‘teleported’ to b. But B needs the information gained that
A gained in the a+c measurement in order to make any sense
of the information teleported to b. And that can only be sent
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INTERVIEW Ball 375
classically, no faster than the speed of light. In other words, al-
though the collapse of entanglement that sends the state of c
onto b happens instantaneously, quantum teleportation can’t be
used to transmit information faster than light.
NSR: What are the major technologies that are needed for a
quantum internet? Could the existing bre-optic and satellite
infrastructure support it, or is new infrastructure needed, for
example?
Pan: Generally, the quantum internet will consist of nodes that
processand storequantum information, and channels that trans-
fer quantum information. e nodes are complicated and highly
dependent on the specic task at hand. For example, quantum
key distribution (QKD) is the rst practical application of quan-
tum information. In China, the Beijing-Shanghai Backbone Net-
work is already built and put into use. A QKD terminal must
be capable of producing, manipulating and measuring single
photons.
e best particle for transferring qubits (making ‘ying
qubits’) is the photon. It has the big advantage that laser com-
munication is now quite mature and there is already a mass of
optical infrastructure can be used—so yes, existing bre-optic
channels can indeed be used. However, big modications are
still needed for the quantum internet, especially at the nodes.
As a satellite is extremely hard to modify, we believe that new
satellites are necessary [tailored to quantum communication
and processing]. ere are some cases where quantum payloads
could be added to existing scheduled satellites, for example with
GPS satellites or the European Galileo satellite.
NSR: Is this mainly about making internet telecommunications
more secure, or are there other benets that could come from
encoding information using quantum rules?
Pan: e near-term target is indeed to make telecommunica-
tion more secure. But quantum information can do more than
this. We believe that a practical quantum computer can be built
within a few decades. rough the quantum internet, cloud
quantum computation will be a basic resource in the future.
NSR: What has been achieved so far, and what would be the fu-
ture milestones in creating a system like this?
Pan: We have built the Quantum Secure Communication
Beijing-Shanghai Backbone Network. As the world’s rst long-
distance quantum-secured communication route, it was put into
service on 29 September 2017. e inter-city quantum commu-
nication line, which measures over 2000 km and comprises 32
relay stations, connects the cities of Beijing, Jinan, Hefei and
Shanghai. Data can be transferred through the network with
information-theoretical security. More backbone and inner-city
networks are being planned and will be built. We have launched
the rst quantum science satellite, Micius, on 16 August 2016.
The near-term target is to make telecommunication
more secure.
—Jian-Wei Pan
The quantum internet of the future might be completely
different from what we imagine now.
—Jian-Wei Pan
QKD has been performed between Micius and several ground
stations in China, including Beijing, Delingha, Nanshan, Graz
in Austria and Tenerife in Spain. With the help of the Beijing-
Shanghai Backbone, intercontinental QKD has thus been real-
ized via Micius. More satellites will be launched to constitute a
global network in the future.
NSR: Do we yet have a full understanding of the principles be-
hind a quantum internet, making it ‘just’ a maer of engineering?
Or do you think we might yet discover new things that quantum
physics makes possible for information technology, in the way
that we have already for cryptography and computing?
Pan: We don’t have a full understanding even of the principle
behind the very basic phenomenon of quantum superposition.
However, that doesn’t hamper the applications of quantum
mechanics with the knowledge we already have. is knowl-
edge makes building a QKD network seems like an engineering
project. However, even in this relatively mature domain, new
concepts continue to emerge. For future techniques such as
quantum computation, we still know too lile. e quantum
internet of the future might be completely dierent from what
we imagine now. I think this is the magic of science.
NSR: Does a quantum internet necessarily have any connection
to the development of quantum computers, or is it wholly sepa-
rate? Might a quantum-based telecommunication system enable
distributed quantum computing, for example?
Pan: Yes, it will. I believe that quantum computers will become a
crucial part of the quantum internet. Due to their high construc-
tion cost, quantum computers will be expensive resources, and
so will oer a public service only via the quantum internet—at
least in the early stages. In this scenario, users will access quan-
tum computers through the quantum internet, uploading tasks
and downloading results by transferring qubits. is is the con-
cept of cloud quantum computation.
NSR: What kind of investment is being made internation-
ally in developing a quantum internet? Will it require trans-
national cooperation? Where are the major centres of research
internationally?
Pan: e quantum internet involves lots of theory and technol-
ogy. For the short-term target of building a quantum internet
for global secure communication, we will have to consider the
imperfections of realistic devices. We need beer protocols to
minimize the inuence of engineering imperfections. We need
cheaper and beer devices that oer improved performance and
can work in extreme environments. We need quantum channels
that are widely distributed and easy to use, including both -
bre and satellite links. I can’t imagine that any country can meet
these challenges alone, without international cooperation. We
have a great team here in China, and there are also very good
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376 Natl Sci Rev, 2019, Vol. 6, No. 2 INTERVIEW
teams all over the world. Already there is very good international
cooperation on these problems.
NSR: China has been a leader in this area. Does the Chinese gov-
ernment see this technology as a particularly important one for
future growth of the economy, nance, business and so forth?
Pan: Yes, we have received strong support from the Chinese
government. As I mentioned above, we have built and put into
service the Beijing-Shanghai Backbone Network, and currently
real-world applications by banks, securities and insurance are
being trialled. More than 150 users are now using our Backbone
for secure information transfer. As I also mentioned, we have
launched the rst quantum science satellite, Micius.
NSR: Where do you see this technology being in, say, 20 years
time?
Pan: e cost of QKD will be dramatically reduced. Devices for
QKD will be miniaturized and become suitable for personal use.
QKD will be a common technique for encryption and be widely
used in daily life. Quantum computers or quantum simulators
will be built and run as public services for certain tasks, just as su-
percomputers are today. I don’t think that a universal [general-
purpose] quantum computer that can factorize a large number,
of say 2048 bits, will be built by that stage, we will already know
what such a universal quantum computer should look like and
what we still need to do in order to build one.
NSR: Who or what has been your source of inspiration in this
eld? Would you recommend it as an area for young researchers
to enter?
Pan: I believe both foundational aspects of quantum mechan-
ics and possible practical applications are very important issues.
e original motivation for me to be an experimentalist was to
perform fundamental tests of the laws of quantum mechanics, to
understand how and why it diers from classical physics. How-
ever, the possible practical applications of quantum mechanics
also aract me deeply, since they can make a real dierence to
our lives.
With the invention of the internet, we have entered the in-
formation age. e quantum internet provides another rare op-
portunity to truly change the world. It would enable a scientic
revolution. I will spare no eort to recommend that smart young
researchers engage with this area.
Philip Ball writes for NSR from London.
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