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Julia Kempe

Under ideal conditions, quantum computers can manipulate not just the ones and zeros of classical computers but also delicate superpositions of the two classical states. Potentially, this offers huge advantages in computing power and allows new types of problems to be addressed via computation.

Julia Kempe, a 33-year-old native of Berlin's East German side, maintains herself in a similarly powerful--but delicate--state: Kempe is neither physicist nor mathematician, but a superposition of both. When, after earning no fewer than four degrees in physics and maths, Kempe was pressed to narrow to a single specialisation, she refused to choose, opting instead for a field--quantum computation--that, as she puts it, combines "actual nature" with "beautiful maths." She went on to earn two more degrees--both Ph.D.s--along with a tenured post at the French National Centre for Scientific Research (CNRS) (at age 27) and the Irène Joliot-Curie Prize to the most outstanding young female researcher in France. The keys to her success? Lots of talent, obviously--but also an early start and a seemingly insatiable appetite for knowledge.

An early start

As a child, Kempe's favourite game was mathematics. "It seems it is a cliché, but as far as I remember, I always liked to solve" mathematical problems, Kempe says. In East Germany in those days, gifted pupils were identified in national competitions and placed in specialised schools, so she soon had many mathematical problems to play with. "We learnt general techniques that you can approach problems with," she says. She also met people with similar abilities and interests and won first prizes in regional and national mathematics, physics, and chemistry contests.

When she was 17--a year after the 1989 fall of the Berlin Wall--Kempe moved to Austria with her parents. In 1992, she began to study both maths and physics at the University of Vienna, even though it meant studying for two undergraduate degrees. She earned both degrees--and the university's top award in both disciplines--in 1995.

During the last year of her undergraduate programme, Kempe's penchant for intellectual and geographic wandering emerged. She visited the University of Technology in Sydney, Australia, as an exchange student in theoretical physics, and "when I came back, I decided to go to France," she says. First, she did a Diplôme d´Etudes Approfondies (D.E.A., equivalent to a master's degree) in algebra at the Pierre and Marie Curie University in Paris. Then she did another one in theoretical physics at the Ecole Normale Supérieure . She now had two bachelor's degrees and two master's degrees--and she was only 23.

Studying two disciplines at the Ph.D. level proved trickier--but she was up to the challenge. "All the Ph.D. topics offered were either physics or maths," she says. She couldn't bring herself "to abandon something," as she puts it, so she applied to two graduate programmes focused on different aspects of quantum computation, one at the Department of Computer Science and Networks at the Ecole Nationale Supérieure des Télécommunications in Paris and the other at the Department of Mathematics of the University of California, Berkeley. The idea was to choose one or the other, but she was accepted at both, so in the end she arranged to do the two Ph.D.s simultaneously.

One problem that has to be dealt with before a quantum computer can be built is the intrinsic fragility of quantum states. "A little bit of noise," as Kempe describes it, forces the quantum system--the "qubit"--into one of the classical states, in which case only the two classical states--0 and 1--are available for manipulation. At Berkeley, Kempe sought ways to protect quantum states. Because of the interdisciplinary nature of the work, she had two advisers there, Elwyn Berlekamp from the mathematics department and Birgitta Whaley from chemistry. "Julia is an unusually self-motivated, independent researcher," Berlekamp writes in an e-mail. "By the time she finished her Ph.D., she had already written and published many original research papers and presented her work at several significant conferences. I don't think she needed to learn much more to become an accomplished researcher."

Meanwhile, Kempe travelled to Paris "in the summer, or a month here and there," to work on her second Ph.D., investigating how quantum states could be used in applications other than quantum computers. One such application is cryptology. Although quantum computers may one day be able "to break all the code systems," including the ones used by credit card companies to protect consumers, quantum-mechanical principles may also be used to "make sure that no one interferes with your information," Kempe says. She finished both Ph.D.s in 2001, with prizes from both institutions.

Julia Kempe with a colleague.

Still not ready to settle down

Kempe then applied for a tenured research position at CNRS, planning to gain some postdoctoral experience while she waited for a position to open up, which usually takes a few years. But she got a CNRS offer immediately, at the Computer Science Department of the University of Paris in Orsay, to work on quantum information and computation. It was an excellent gig; these positions are prized because they are permanent and "very flexible," Kempe says. "There is no teaching, and nobody prescribes you what to do, which is very nice."

They are also flexible in another way: The CNRS appointment actually left her free to go abroad and gain experience. So after a couple of months, she went back to Berkeley to work as a postdoctoral fellow. While she was there, her 1-year probationary period at CNRS ended, and she was awarded tenure in France.

She returned to France in 2004, but she continues travelling widely. Travel is important "because our field is small and very spread around the world," she says. "It is very important to be updated with what other people are doing and spread your own work." In 2006, the same year as she won the Irène Joliot-Curie Prize, she also received a CNRS Bronze Medal, given each year to CNRS's most outstanding young researchers in different disciplines. To date, Kempe has 43 publications and seven more in the pipeline.

Kempe downplays her success and the variety of her activities. "It is easier than you imagine," she says. "I'm always doing the same thing. The question is where I do it"--and in what scientific context.

How has she managed to accomplish so much while still so young? Her early start in mathematics helped, she believes. She also believes that being a woman in traditionally male-dominated disciplines works in her favour. "People remember you, and I get invited more," she says. Remarkably, another key, she says, is moderation. "I have observed for myself that when I feel that I need to work a lot, I get much less efficient," she says. "I achieve 10 times more when I have a healthy balance." A favourite diversion is dancing; she takes two or three tango classes a week, she says.

Kempe looks forward to the day the quantum balancing act has been perfected and a quantum computer has been built--"What I hear from experimentalists is ... 15 to 20 years or more"--but until then she remains poised to tackle any new challenges that come her way, while revelling in her field's intellectual variety. Her intellectual breadth may be a passionate preoccupation, but it is a way of playing it safe. "I don't get buried into one specialised field," she says. "The fact that I had to learn many things and that I know more about computer science" keeps her opportunities wide and her enthusiasm high.

Even now, Kempe isn't settling down. Last month, she started another leave from CNRS to accept a senior lecturer position in the Department of Computer Science at Tel Aviv University, supported by a 3-year Alon Fellowship from the Higher Council of Academic Research in Israel. Behind the move are "a lot of professional needs," she says--and one personal motive. "I hope to catch up on the science computing thing," Kempe says, and the move allows her to reunite with her long-term partner, also a scientist.

Despite her apparent restlessness, there is one aspect of settling down that Kempe has begun to look forward to: She is eager to start a scientific family, as it were. "At this point of my career, I have worked alone and for myself," she says. "I should start taking more students and get a group soon."

The call for applications for the 2007 Irène Joliot-Curie Prize closes on 15 June. In addition to rewarding a young scientific woman, it also acknowledges the achievements of a senior female scientist, a mentor, and a woman who has made an outstanding mark in industry. The 2006 winner for the last category was Françoise Heilmann-Pascal, also profiled on Science Careers.

Elisabeth Pain is contributing editor for South and West Europe.

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DOI: 10.1126/science.caredit.a0700067