[Editors] Super-cool MIT work could expose quantum behavior

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

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Super-cool MIT work could expose quantum behavior
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For Immediate Release
THURSDAY, APR. 5, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

PHOTOS AVAILABLE

CAMBRIDGE, Mass.--Using a laser-cooling technique that could one day 
allow scientists to observe quantum behavior in large objects, MIT 
researchers have cooled a coin-sized object to within one degree of 
absolute zero.

This study marks the coldest temperature ever reached by 
laser-cooling of an object of that size, and the technique holds 
promise that it will experimentally confirm, for the first time, that 
large objects obey the laws of quantum mechanics just as atoms do.

Although the research team has not yet achieved temperatures low 
enough to observe quantum effects, "the most important thing is that 
we have found a technique that could allow us to get (large objects) 
to ultimately show their quantum behavior for the first time," said 
MIT Assistant Professor of Physics Nergis Mavalvala, leader of the 
team.

The MIT researchers and colleagues at Caltech and the Albert Einstein 
Institute in Germany will report their findings in an upcoming issue 
of Physical Review Letters.

Quantum theory was developed in the early 20th century to account for 
unexpected atomic behavior that could not be explained by classical 
mechanics. But at larger scales, objects' heat and motion blur out 
quantum effects, and interactions are ruled by classical mechanics, 
including gravitational forces and electromagnetism.

"You always learn in high school physics that large objects don't 
behave according to quantum mechanics because they're just too hot, 
and the thermal energy obscures their quantum behavior," said Thomas 
Corbitt, an MIT graduate student in physics and lead author of the 
paper. "Nobody's demonstrated quantum mechanics at that kind of 
(macroscopic) scale."

To see quantum effects in large objects, they must be cooled to near 
absolute zero. Such low temperatures can only be reached by keeping 
objects as motionless as possible. At absolute zero (0 degrees 
Kelvin, -237 degrees Celsius or -460 degrees Fahrenheit), atoms lose 
all thermal energy and have only their quantum motion.

In their upcoming paper, the researchers report that they lowered the 
temperature of a dime-sized mirror to 0.8 degrees Kelvin. At that 
temperature, the 1 gram mirror moves so slowly that it would take 13 
billion years (the age of the universe) to circle the Earth, said 
Mavalvala, whose group is part of MIT's LIGO (Laser Interferometer 
Gravitational-wave Observatory) Laboratory.

The team continues to refine the technique and has subsequently 
achieved much lower temperatures. But in order to observe quantum 
behavior in an object of that size, the researchers need to attain a 
temperature that is still many orders of magnitude colder, Mavalvala 
said.

To reach such extreme temperatures, the researchers are combining two 
previously demonstrated techniques-optical trapping and optical 
damping. Two laser beams strike the suspended mirror, one to trap the 
mirror in place, as a spring would (by restoring the object to its 
equilibrium position when it moves), and one to slow (or damp) the 
object and take away its thermal energy.

Combined, the two lasers generate a powerful force-stronger than a 
diamond rod of the same shape and size as the laser beams-that 
reduces the motion of the object to near nothing.

Using light to hold the mirror in place avoids the problems raised by 
confining it with another object, such as a spring, Mavalvala said. 
Mechanical springs are made of atoms that have their own thermal 
energy and thus would interfere with cooling.

As the researchers get closer and closer to reaching the cold 
temperature they need to see quantum behavior, it will get more 
difficult to reach the final goal, Mavalvala predicted. Several 
technical issues still stand in the way, such as interference from 
fluctuations in the laser frequency.

"That last factor of 100 will be heroic," she said.

Once the objects get cold enough, quantum effects such as squeezed 
state generation, quantum information storage and quantum 
entanglement between the light and the mirror should be observable, 
Mavalvala said.

Other authors on the paper are Christopher Wipf, MIT graduate student 
in physics; David Ottaway, research scientist at MIT LIGO; Edith 
Innerhofer (formerly a postdoctoral fellow at MIT); Yanbei Chen, 
leader of the Max Planck (Albert Einstein Institute) group; Helge 
Muller-Ebhardt and Henning Rehbein, graduate students at the Albert 
Einstein Institute; and research scientists Daniel Sigg of LIGO 
Hanford Observatory and Stanley Whitcomb of Caltech.

The research was funded by the National Science Foundation and the 
German Federal Ministry of Education and Research.

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Written by Anne Trafton, MIT News Office