X-Message-Number: 29401
From: "Basie" <>
Subject: Laser-cooling Brings Large Object Near Absolute Zero
Date: Sun, 8 Apr 2007 15:37:39 -0400

Laser-cooling Brings Large Object Near Absolute Zero
Science Daily - 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.

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.

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.

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.

http://www.sciencedaily.com/releases/2007/04/070406171036.htm

Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=29401