http://www.boston.com/news/globe/ideas/articles/2007/03/18/qa_with_lene_hau
Originally appeared in the Boston Globe
By Harvey Blume
As the Danish physicist Lene Vestergaard Hau, a tenured
professor at Harvard, explained to me how she slows light down -- and, when
it's going at a "comfortable bicycling speed," does something to it
that's weird even by the standards of quantum mechanics -- I couldn't resist
blurting out the suspicion I'd harbored since reading about her work:
"You're going to win a Nobel Prize if you're not careful." Hau, one
of nine MacArthur Fellows picked by the MacArthur Foundation in 2005 to
represent the history of its "genius" awards, just laughed and went
back to energetically explaining the apparatus she had built to experiment with
light.
Hau succeeded by cooling sodium atoms down almost to
absolute zero, creating what is known as a Bose-Einstein condensate. She then
discovered that such a condensate works like "optical molasses," as
she put it, on incoming light. (For more detail, see deas.harvard.edu/haulab.)
Hau was initially drawn to working with slow light because
she expected it would be "new territory, a new regime of nature."
Early this year she made a foray into that new territory with a
widely-publicized experiment that can sound like death and resurrection on the
quantum scale. After once again crashing a light beam into a sodium condensate,
she extinguished the light. The condensate drifted into another such
condensate. Then, stroking the second condensate with a laser, Hau released a
light beam identical to the original pulse, and sent it on its high-speed way.
IDEAS: You clearly take pleasure in slowing light.
HAU: I absolutely do! There's a tremendous amount of work
building the apparatus, getting the experiment to work. But sitting there late
at night in the lab, and knowing light is going at bicycle speed, and that
nobody in the history of mankind has ever been here before -- that is
mind-boggling. It's worth everything.
IDEAS: What are the practical applications?
HAU: Perhaps you remember that when Charles Townes invented
the laser, he was asked: What do you think the applications of this laser can
be? He scratched his head, thought about it, and said: "Well, if you place
a laser on the head of the typewriter, and make a typo, you can zap the
typo." That was the wildest thing he could imagine for lasers. Think about
what we do with lasers now.
We're bound to find new fundamental physics and new
applications for slow light. What exactly? It's exciting to start exploring.
IDEAS: Are there implications for computing?
HAU: Sure. To get high data transfer rates in communicating
information, you would love to use optical fibers. The problem is that light is
extremely hard to manipulate. So we make a perfect copy of the information
carried by the light. We transfer it to matter -- the condensate.
The matter copy is more long-lived. You have time to do all
sorts of things to it. And matter is extremely easy to manipulate. You can grab
onto it, massage it with laser beams, squish it, change it, and convert it back
into light.
IDEAS: So you foresee your work playing a role in computers
that perform or calculate with light rather than electricity. Are there also
theoretical implications to your work?
HAU: By asking that, you are splitting, making a distinction
between theory and experiment. To me, what makes physics physics is that
experiment is intimately connected to theory. It's one whole. Physics is about
questioning, studying, probing nature. You probe, and, if you're lucky, you get
strange clues.
If that part is not there, it's mathematics.
IDEAS: The Large Hadron Collider, the most powerful particle
accelerator ever, is about to go into operation in Switzerland. Will you be
involved?
HAU: I work at the opposite end of the energy scale. Those
guys are up here with billions of electron volts. I'm down here at a billionth
of an electron volt.
The interesting thing -- coming back to theoretical
implications -- is that in working with Bose-Einstein condensates we get a
tremendous sensitivity. When we create slow light and odd states of matter, we
rely on quantum mechanical effects that tend to be very fragile.
Our systems could be extremely sensitive detectors, giving
us a different way of probing some of the fundamental questions of physics --
gravity, for example, and extra dimensions, if they exist.
IDEAS: It has been argued that string theory has a
stranglehold on physics. As I understand it, string theory tries to unite the
macrocosm, gravity, for example, with the microcosm, with quantum mechanics.
Are there other models than string theory?
HAU: Even if there are no competing models, that doesn't
mean that string theory is right. What is bothersome is you have many people
working on it, but it doesn't seem to be testable. Until there are testable
consequences, in some sense, it is math.
IDEAS: How did you get interested in physics?
HAU: I thought I would become a mathematician when I started
college in Denmark. Studying quantum mechanics changed my mind. I thought it
was absolutely fascinating. It hooked me on physics.
IDEAS: Quantum mechanics is full of paradox, isn't it?
Aren't you ever disturbed by it?
HAU: Yeah. Then again I like to be disturbed.
IDEAS: You're a tenured professor of physics at Harvard,
where there's been a lot of debate about women and science. What is your
experience?
HAU: That's a hard one, a hard one. If you look around the
other sciences, you see great progress for women, partly because of women
entering colleges since the '60s. But physics somehow hasn't moved. Why is
that? I don't know. To me, it's odd. It feels totally natural for me to be in
physics.
IDEAS: Is it difficult for you to be in a department with
mostly men?
HAU: Men have learned to deal with women as students or
junior faculty. But there's a phase change when women are actually tenured
faculty. Many men -- I shouldn't just say men, many women, many people -- have
a hard time dealing with different backgrounds, different points of view.
I don't particularly want to have clones of me running
around. That's pretty boring. I have been very surprised. I think I figured
something out, I have the perfect argument. Then somebody who has also thought
about it brings up an argument: Oh, I hadn't even thought about that.
IDEAS: Are you talking about your discipline or more
generally?
HAU: More generally, about the openness I thought would be
in academia. But academia is actually very conservative. You would have thought
these scholars, particularly if they have tenure, would have the freedom to be
free thinkers. But in many cases you see close-mindedness.
Harvey Blume is a writer based in Cambridge.
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