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(Almost) Absolute ZeroParkland Middle School
9 January 2008William D. Phillips
Laser cooling and trapping groupNational Institute of Standards and
TechnologyGaithersburg, Maryland USA
andThe Joint Quantum Institute: NIST and the
University of Maryland
The Science of Cold
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NIST is one of the most important laboratories in the world for research on getting to the coldest possible temperatures.
NIST and Absolute Zero
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NIST is one of the most important laboratories in the world for research on getting to the coldest possible temperatures.
NIST and Absolute Zero
Why?
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Luis
Luis Orozco is Professor of Physics at the University of Maryland and a researcher with the Joint Quantum Institute, a collaboration between the university and NIST dedicated to the goals of controlling and exploiting quantum systems.
“...if we have cold atoms and they're moving very, very slowly, then I should be able to learn a lot and get information out of those atoms.”
--from a PBS interview about Absolute Zero
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What does NIST do?Among other responsibilities, the National Institute of Standards and Technology is the keeper of the the standards of measurements for the United States.
length
time
mass
Images Copyright Shutterstock
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It’s about TIME!
Why does NIST care about making things cold?
When Einstein asked himself “What is time?”, he answered: “Time is what a clock measures.”
(but what IS “time”?)
Images Copyright Shutterstock
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The best clocks are atomic clocks: the atoms are the
tickersquartz crystal tuning fork
(the ticker of a quartz watch)Artist’s
cartoon of an atom
The crystal vibrates at a specific frequency, each
one a little different.
Atoms also “vibrate” at specific frequencies; all atoms of the same type are perfectly identical.
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Who cares?
GPS satellite.
One reason we need atomic clocks is the Global Positioning System.
Atomic clocks in satellites guide
cars, planes, backpackers, and military vehicles.
For improved navigation, communication, scientific research, and national security, we are always trying to improve atomic clocks, but we hit a snag because the
atoms move so fast.
Image Copyright ShutterstockImage NASA
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Atoms in a gas are moving really fast,
and that makes it hard to measure their ticking.
Fast gas atoms make a
fast atomic beam.
about 200 meters/sec
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The Absolute or “Kelvin” temperature scale
300 K => room temperature273 K => ice melts
0 K => absolute zero
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The Absolute or “Kelvin” temperature scale
0 K => absolute zero
300 K => room temperature
195 K => dry ice
273 K => ice melts
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The Absolute or “Kelvin” temperature scale
0 K => absolute zero
300 K => room temperature
195 K => dry ice
273 K => ice melts
185 K => a cold day in Antarctica
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The Absolute or “Kelvin” temperature scale
0 K => absolute zero
300 K => room temperature
195 K => dry ice
77 K => liquid nitrogen
273 K => ice melts
185 K => a cold day in Antarctica
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QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
How do we cool something without touching it?
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QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Halley’s comet
We use radiation pressure to push on atoms and make them slow down.
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The Absolute or “Kelvin” temperature scale
0 K => Absolute Zero
300 K => room temperature
195 K => dry ice
77 K => liquid nitrogen
273 K => ice melts
185 K => a cold day in Antarctica
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The Absolute or “Kelvin” temperature scale
0 K => Absolute Zero
300 K => room temperature
195 K => dry ice
77 K => liquid nitrogen
3 K => outer space
273 K => ice melts
185 K => a cold day in Antarctica
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T = 700 nK!
This is 100 million times colder than liquid nitrogen, about 4 million times colder than the temperature of outer space.
By measuring the velocity of the atoms, we could determine the temperature of laser-cooled atoms. By 1995, we had cooled a gas of cesium atoms to:
What sort of clock can we make with atoms this cold?
The thermal velocity of these atoms is
Vthermal < 1 cm/s
This was about 200 time COLDER than everybody thought was
possible!
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Today’s laser cooled clocks are the most accurate primary time standards ever made: better than one second in
60 million years !
laser cooled clock performance
But other scientists at NIST have gotten even colder than my team was able to get with laser cooling. Eric Cornell and his team started with laser cooling and then used evaporation.
But what do we use for a container? No material vessel, hot or cold, will do. We use a magnetic bottle.
Einstein drawing by Bülent Atalay
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From next week’s NOVA program, let’s listen to Eric Cornell tell about the
coldest gas ever made, a new state of matter, which won him and his
colleagues the 2001 Nobel Prize in Physics
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10 000 K
100 K
1 K
10-2 K
10-4 K
10-6 K
10-8 K
10-10 K
10-12 K
surface of the sun: 5000 Kroom temperature: 300 K
outer space: 3 K
liquid nitrogen: 77 K
laser cooling: 0.7 K
Bose-Einstein Condensation: 1 nK
BEC in space (the future):1 pK
logarithmicthermometer
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What’s Next?
• Better clocks
• Tests of the fundamental understanding of Nature
• Quantum Computers
• More...