laser fits on a chip
Technology Research News
Figuring out how to coax electrons to flow
through wires etched in silicon chips has produced many returns. Televisions,
computers, cheap electronic toys, and many kinds of sensors all contain
Using computer chips to line up photons into laser beams has also helped
bring about technologies as diverse as compact discs and high-speed telecommunications.
An emerging area of research that promises to enable new technologies
is figuring out how to control beams of atoms. A group of researchers
from the Max Planck Institute in Germany has taken a large step in that
direction by demonstrating that it is possible to herd a cloud of atoms
around a silicon chip.
Since Massachusetts Institute of Technology physics professor Wolfgang
Ketterle and his colleagues made the first atom laser in 1997, scientists
have been able to focus beams of atoms in much the same way lasers focus
beams of photons. Ketterle and two of his colleagues received the 2001
Nobel Prize in physics last week for discovering the form of matter used
in atom lasers.
Today's atom lasers are very bulky, however. Being able to control atoms
on a chip makes the technique much more practical.
Controlling atoms on a silicon chip is similar to the miniaturization
process that made computer chips commonplace, said Jakob Reichel, a research
assistant at the Max Planck Institute for Quantum Optics at the University
of Munich. "[It] can be compared to the step from discrete transistors
to integrated microelectronics," he said.
It paves the way for miniaturized versions of very accurate measuring
devices like atomic clocks and acceleration sensors, and will make it
easier to study the nature of atoms; it is also a step toward making practical
The key to corralling atoms on a chip was keeping the gas atoms in a frigid
Bose-Einstein condensate contained in close proximity to the much warmer
chip. "The main uncertainty was whether the fragile, ultra-cooled quantum
state would survive being so close to the surface of the chip, which is
at room temperature," said Reichel.
Normally, atoms act independently of each other, but when a gas is cooled
to less than one degree above absolute zero it can form a Bose-Einstein
condensate, where all the gas atoms have the same properties. Absolute
zero is -273 degrees Celsius. One of the strange properties of quantum
particles like atoms and photons is that they also act like waves. In
a Bose-Einstein condensate, like laser light, the crests and troughs of
the particles are in sync.
The researchers preserved the fragile Bose-Einstein condensate by using
magnetic fields to hold the cloud of coordinated atoms a fraction of a
millimeter above the chip surface. This is in contrast to electrical circuits,
where the electrons travel through the wires on a chip.
To coax the rubidium atoms to form a Bose-Einstein condensate the researchers
used the standard method of several cycles of evaporation to cool them
to less than one degree above absolute zero. The efficiency of their trap
also reduced the cooling time of the atoms, allowing them to create a
Bose-Einstein condensate in less than one second, which is three to ten
times faster than existing methods, according to Reichel. The short condensation
time made it more difficult for impurities to destroy the condensate.
The researchers then used electromagnetic fields generated by current
flowing within 50-micron wires patterned on the surface of an 18- by 22-millimeter
chip to hold the cloud of 3,000 rubidium atoms 100 microns above the surface.
A micron is one thousandth of a millimeter.
A group of researchers from Tübingen University in Germany has also demonstrated
an atom chip by trapping a Bose-Einstein condensate of 40,000 rubidium
atoms on a 25- by 0.1-millimeter chip in a similar manner. That experiment
used copper conductors that ranged from 3 to 30 microns wide.
The Max Planck researchers took the technology a second step forward by
moving the clouds of cold atoms around the surface of the chip with an
oscillating electrical current in the chip's wires to make a sort of magnetic
"For electrons, there are wires, and for light, we have fibers. A possible
equivalent for condensed atoms is our conveyor belt," said Reichel. "Now
we can... prepare the condensate at one place on the chip, then move it
to another place where it measures something or interacts in some other
way, and finally move it to a third place," to extract the information
The effort is an important development in a push to miniaturize atom optics,
which could eventually foster a "whole new technology," said
Edward Hinds, a physics professor at the University of Sussex and director
of the University's Center for Optical and Atomic Physics. "This experiment
is one step in a whole program being driven forward by half a dozen groups
in Europe, USA, and Japan... to bring atom optics onto a chip," he said.
The ability to manipulate streams of atoms could lead to practical uses
as diverse as those that developed after humans discovered how to manipulate
streams of electrons, said Hinds. "Electronics has proved good for making
a variety of instruments -- TV, radio, telephone, robots, sensors, computers
-- that were not entirely clear when the basic methods were being developed,"
The practice of manipulating atoms on a chip "is still very primitive,
so we don't really know the best [uses for them], but it is already clear
that atom chips will make very good devices for measuring gravity," for
example, said Hinds.
The research is also relevant to quantum computing, Hinds said. "It will
also become possible to look at how the phase [or wiggling of the atom
wave] of the BEC can be manipulated, and how it is affected" by the
chip environment, he said. "These are important issues in learning how
to design and build quantum computers," he said.
Quantum computers can, in theory, manipulate atoms to do certain computations
that are beyond the reach of even the fastest possible classical computer.
Quantum computing schemes use quantum particle traits like spin to store
the ones and zeros that represent information in computing. Particles
like atoms and electrons have one of two types of spin, which can be likened
to a top spinning clockwise or counterclockwise. In theory, quantum computers
could manipulate the spins of a set of atoms like those in a Bose-Einstein
condensate to perform calculations that crack secret codes or search large
In addition, atom chips promise to reveal secrets about the nature of
quantum gases, Hinds said. For instance, "a Bose-Einstein concentrate
on a chip can be squeezed into a long thin tube, or a very flat pancake,
where it's properties are predicted to be very different," he said.
It will take roughly five years for portable, integrated atom interferometers,
which are used as ultraprecise measuring instruments, to be made from
atom chips, said Reichel.
Reichel's research colleagues were Wolfgang Hänsel, Peter Hommelhoff and
Theodor W. Hänsch of the Max Planck Institute and the University of Munich.
They published the research in the October 4, 2001 issue of the journal
Nature. The research was funded by the Max Planck society, the European
Union (EU), and the University of Munich.
Timeline: 5 years, > 10 years
Funding: Government, Private, University
TRN Categories: Quantum Computing
Story Type: News
Related Elements: Technical paper, "Bose-Einstein Condensate
on a Microelectronic Chip," Nature, October 4, 2001; Technical paper,
"Bose-Einstein Condensate in a Surface Micro Trap," posted on the arXiv
physics archive at http://arXiv.org/abs/cond-mat/0109322.
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