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Pan's Dream

By Stefanie Schramm

Chinese physicist Pan Jianwei plans to re-invent communication and computers - with quantum mechanics German bread and sausage are helping him do it.

Pan's Dream© Stefanie SchrammPan Jianwei is working on bug-proof encryption
Wielding a huge knife, Pan Jianwei hacked the universe into tiny pieces. »It felt pretty good«, says the physicist. »I was just about to discover the theory of everything.« Then he woke up.

In real life, Pan is less concerned with the big picture than with tiny fragments. Physicists call these fragments quanta: the smallest pieces a physical value can be divided into. At the University of Science and Technology of China (USTC) in Hefei, Pan is trying to accomplish great things with these tiny quanta - ultra-fast computing and absolutely secure communication. Together with his colleagues he has published 60 articles in top international journals over the past eight years, putting Hefei firmly on the world map of quantum physics.

The capital of Anhui province, three hours from Shanghai by train, is a typical second-tier Chinese city: nearly five million inhabitants, grey, faceless and a little grimy. But in terms of science, Hefei is in China's premier league. Three national research centres are located here; the only place home to more is Beijing. Pan studied in Hefei, went to Innsbruck in 1996 and later to Vienna to complete his doctorate under the supervision of renowned quantum physicist Anton Zeilinger, who has been tipped as a candidate for the Nobel Prize for years. Then Pan moved to Germany and built up his own working group at the University of Heidelberg, while also holding a professorship at USTC and commuting between Heidelberg and Hefei. Since 2008 he has been living in China again. »I love science, but I also love my country«, says Pan. »As soon as I was certain that I could conduct good science here, I returned.« The Chinese state has contributed to this certainty - with research funding of almost ten million euros.

»We just couldn't keep up with that«, says Dirk Dubbers, director of the Institute of Physics at Heidelberg University. »We would have liked to keep Pan, after all he publishes something stunning almost every month.« He came to know the quantum physicist as extremely single-minded. »He never looked left or right«, says Dubbers, and he says it with admiration. »He is very good at recognising what will bring him closer to his goals and what won't«, agrees Caslav Brukner, who completed his doctorate alongside Pan. »And he sees possibilities that others don't see.« Anything that doesn't help him achieve his goals, Pan simply omits; for example, he never learned German despite living in a German-speaking environment for twelve years, recounts Brukner, adding that he also cannot remember ever sharing an after-work drink with his colleague. Pan is now a hai gui - a Chinese term for someone who has returned, but it also sounds similar to the word for »sea turtle«. Just as these animals return to their place of birth to lay their eggs, the Chinese government hopes that highly educated experts will come back to their native country. Special state programmes are enticing specialists to return home - with increasing success.

Pan is pretty sure of what he has already achieved in Hefei. At first sight he looks like the prototype of a reclusive physicist in his grey knitted sweater with the overlong sleeves into which his hands almost disappear. He speaks calmly and matter-of-factly, but he isn't unnecessarily modest. In a PowerPoint presentation he lists the achievements of his team: it is the only laboratory for quantum information in China that has published in Nature; three quarters of all Chinese articles on experimental work in this field published in renowned journal Physical Review Letters were written here; papers from Hefei have twice been named »Physics Story of the Year« by the American Physical Society, and so on.

Pan works mainly in two fields, namely quantum communication and the development of a quantum computer. »Building a superfast computer is very attractive to me personally«, he says. But quantum communication is more important for China, he explains, because it is already closer to application. »Also, we can be among the best there, instead of just trying to catch up with the others.« This is important. The Chinese government has issued a slogan for it: zizhu chuangxin - independent innovation. Pan's innovation is the size of a wardrobe and costs 50,000 euros. »A quantum telephone«, he explains. »In a few years everyone will be able to have one at home.« The device uses quantum mechanically entangled photons to encode and decode messages. »Quantum communication would be very useful for banking transactions and secret messages.«

In the summer of 2008, Pan used the device for the first time to speak to his colleagues in two other locations in Hefei. »The world's first quantum cryptography network for the telephone«, says Pan. »Absolutely bug-proof.« Three months later, the European SECOQC consortium set up a network with six nodes. The homecomer of Hefei is conducting globally leading research. For his private communications Pan continues to use a standard Internet connection and a laptop. His children still live in Heidelberg with his wife. »I call them every evening over the Internet, when it's afternoon where they are«, he says. The little clock in the corner of his screen still shows German time. »I tell them fairy stories I make up myself«, says the physicist, suddenly not so matter-of-fact anymore. »We're all in them; my son has a magic wand and my daughter has a ring that can beam us anywhere we want.«

As a little boy, Pan loved books like Jules Verne's Twenty Thousand Leagues Under the Sea. Today he reads Harry Potter in his limited spare time. »I haven't got round to the last three volumes yet«, he admits. And he likes Star Wars. »It inspires the imagination.« A bit more of that would do Chinese science good, according to Pan: »There is still a lack of creativity among Chinese researchers.« One reason for this, he says, is the incredible pressure pupils in China are under. A single exam decides whether they get a place at a good university; they study for this for years. »Then they know a lot, but are often incapable of developing independent solutions«, says Pan. It would however be difficult to change the selection system, he concedes, because there are simply too many pupils.

What he particularly liked about Europe, says the physicist, was the »quiet life«, which he thinks is good for science. And he also liked the politics, he says, but then stops, not wanting to be drawn into a political discussion. Instead, he reports that he still eats a German breakfast. »I immediately looked where I could get bread and sausage in China.« Just as important as the knowledge the returnees bring back, believes Pan, is the scientific culture. This evidently makes itself felt rather quickly. His former colleague Brukner met Pan's students at a conference in Beijing and was surprised: »Normally Chinese students don't like to question their teacher, but Pan's people are different, very keen on discussion.« The homecomer himself says he also benefited from his time abroad because he found role models there, which are a necessity for a researcher: »The fathers of Nobel Prize winners were often also scientists.« Such outstanding role models are still rare among China's researchers. Pan is well on his way to becoming one.

His international reputation depends especially on how his favourite project, the quantum computer, develops. Pan's group is part of the small field of laboratories that are vying for the world record in a very specific discipline: forming jittery quantum particles into stable constructions, so-called cluster states. This is fundamental to tomorrow's technology. In a quantum computer, qubits do the computing work. As opposed to normal data bits, they can take on more than one value at a time - delivering several computing operations for the price of one. If these qubits are additionally entangled so that their properties are linked, various calculations can be performed simultaneously on a huge number of inputs. These two tricks would make it possible to build an extremely fast computer.

The problem: entanglements are extremely fragile, but normally have to be adjusted for every computing step. Cluster states on the other hand are prepared for each step before performing the calculation, and then left alone. In 2007, Pan was the first to create a cluster state of six qubits with six photons. Now he is working on expanding this construction; a new publication has already been submitted. Nonetheless, work on the superfast computer is currently only progressing in tiny steps, qubit by qubit. It's still a long way from practical application; a reasonably demanding calculation would require 50 to 100 entangled qubits. »At the moment, the mathematical abilities of our quantum computer are no better than those of a ten-year-old«, says Pan and grins. It will take twenty years at least, he expects, until his computer is grown up. But Pan is optimistic; he had another dream: »I saw this quantum computer, it was standing right in front of me on the desk.« But the supercomputer wasn't really tangible. »It was a mixture of solid and fluid that kept changing its shape. And it shimmered blue.«

Pan Jianwei is one of China's most high-profile physicists. His laboratory at the University of Science and Technology in Hefei is among the world's top institutes in quantum physics. Pan completed his doctorate with leading quantum physicist Anton Zeilinger in Vienna before working in Heidelberg for five years. In 2008 he returned to his home country - the Chinese government had enticed him with research funding of ten million euros. The physicist is working on bug-proof encryption. Pan Jianwei developed the world's first quantum cryptography network for the telephone, which consisted of three nodes. He also plans to build a quantum computer. In his free time he invents fairy stories for his children. A bit more imagination would do Chinese science good, he says.

From DIE ZEIT :: 11.02.1010