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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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How do clocks measure time?

Different clocks have different “tickers.”

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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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My goodness, it’s 12:15:0936420175. Time for lunch

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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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COLD:

slow atoms

HOT:

fast atoms

Hot and Cold

13Demonstrations

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The Absolute or “Kelvin” temperature scale

0 K => absolute zero

300 K => room temperature

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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

19pull out balloons

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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

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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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Na Optical Molasses

How cold are these atoms?

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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!

27Copyright Geoffrey Wheeler

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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

29trapping

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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...

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The End