Young Scientists
Mikio Kozuma
Dr. Mikio Kozuma
Dept. of Basic Science, University of Tokyo
3-8-1 Komaba Meguro-ku, Tokyo 153-8902, JapanDr. Kozuma received his Ph. D degree from Departmentof Applied Physics in Tokyo Institute of Technology in 1997
and joined Dr. W. D. Phillips’s group in National Instituteof Standards and Technology (U. S. A.) as a postdoc.
Since 1998, he is a research associate in Prof. Kuga’sgroup at University of Tokyo.

“GO HOME and SLEEEEEP!”, Lu shouts.
“This experiment is KILLING US”, Ed shouts. I
was just saying, “Something is wrong. Something is wrong....” “Yes, something is wrong,that’s why the experiment doesn’t work!” Edand Lu laughed simultaneously. It was alreadypast midnight and we were still trying to develop the technique of optically induced Bragg
diffraction of Bose-Einstein condensed
sodium atoms. The objective was to split thewavefunction of the condensate coherently.
My friends Ed and Lu got the idea to make awell-collimated continuous wave atom laser,and Bragg diffraction was a key step towardmaking it. We checked everything and, in principle, it should have worked. But nothing happened.
Two years before, when I was a Ph.D. student at the Tokyo Institute of Technology under the guidance of Professor Ohtsu, I was engaged in experimental research on laser cooling and trapping of neutral atoms. If one irradiates atoms with properly chosen laser beams,
their temperature can be reduced dramatically.
In fact, one can cool atoms to a few microkelvin(a millionth of a degree above absolute zero!)within one second. As the temperature (or thekinetic energy) of the atoms decreases, the spatial size of the atomic wave packet (thermal DeBroglie wavelength) increases. When the temperature reaches a critical value where thewavelength is long enough for these wave
packets to overlap significantly, then suddenly
the atoms should start sharing the same quantum state. This is referred to as Bose-Einsteincondensation (BEC) and it only happens withbosons. Unfortunately, laser cooling by itself
could not allow us to enter this regime. In fact,
there is no single method that can be used to26

JSAP International No.3 (January 2001)

reach such an extremely low temperature.
Therefore, one must combine several techniques such as laser cooling, magnetic confinement, and radio frequency excitation. The final mechanism on the road to BEC usually involves a technique called evaporative cooling.
People use this technique every day to cool theircoffee or soup by blowing on it. The idea is toremove the hot atoms and leave behind cooler
ones that re-thermalize to a lower temperature.
When the temperature of the trapped atoms
is sufficiently low, a phase transition occurs andalmost all atoms jump into a single quantum
state. The observation of such phase transitions had been the holy grail of the atomic
physics community and I was very interested insuch studies.
After I received my Ph.D., I went to workin Dr. W.D. Phillips’ laboratory at the National
Institute of Standards and Technology (NIST) in
the United States as a research scientist. Upon
arriving at NIST I immediately joined a team ofresearchers attempting to achieve Bose-Einsteincondensation with sodium atoms. We workedfor over a year on rebuilding the entire apparatus towards this goal. It was a very challenging task and after countless sleepless nights
spent in the lab; we finally managed to produce our first condensate in the early hours ofthe morning of January 25th, 1998. We continued to push on and advance the knowledge
in the field by first developing Bragg diffraction techniques that have been widely adopted
by many groups around the world, including
MIT.
Although our experiment initially did notwork as planned, we soon realized that its failure was most likely due to our inability to hit
the small condensate. In principle, we could

have calculated its position in the ultrahighvacuum cell and aligned the laser beam to it,
but there were always problems with vibrations
that caused the condensate to move inside thetrap. We therefore concluded that the fastestand surest way to ensure the proper illumination of the condensate was to use a larger laser beam diameter. Ed said, “Now no atom
can escape us. There’s no place for the atoms
to hide!”. We redid the experiment aroundthree o’clock in the morning and it immediately succeeded[1]. About one month later, weused this Bragg diffraction technique to develop
a well-collimated atom laser that emitted coherent matter waves just as an ordinary laser
emits coherent light waves[2].
After my postdoc in the United States, I
accepted a research assistant position in Professor Kuga’s laboratory at the University ofTokyo. Although taking that position in Japan
meant leaving Lu and Ed, our collaboration hascontinued to this day. It has yielded results suchas the first coherent, matter-wave interferometer and the first phase-coherent amplificationof matter waves[3]. The latter is analogous tolaser amplifier, which led to practical applications of laser technology.
The future of this field is bright, and there
are still many outstanding questions that remain to be answered. We are happy that wewere fortunate enough to work in this exciting
field, and we are grateful that we were able to
make contributions to it. As for my friends Luand Ed, we still continue our collaboration andhope that the future will be as fruitful as thepast.

References[1]. M. Kozuma, L. Deng, E. W. Hagley, J.
Wen, R. Lutwak, K. Helmerson, S. L.
Rolston, and W. D. Phillips, Physical Re
view letters, 82, 871 (1999).
[2]. E. W. Hagley, L. Deng, M. Kozuma, J.
Wen, K. Helmerson, S. L. Rolston, andW. D. Phillips, Science, 283, 1706 (1999).
[3]. M. Kozuma, Y. Suzuki, Y. Torii, T. Sugiura,T. Kuga, E. W. Hagley, and L. Deng,Science, 286, 2309 (1999).