paul c. haljan university of michigan oct. 2003. i. laser cooling atoms magnets lasers

Paul C. HaljanUniversity of MichiganOct. 2003

I. Laser cooling atoms

Magnets

Lasers

II. Quantum Tornadoes Near Absolute Zero

Courtesy NOAA

Cd+Cadmium quantum bits

The world circa 1920’s

Air = molecules moving around!

Atomic constituents

Light

and radio waves …..

Fifth Solvay Conference 1927“Electrons and photons”

Quantum Theory – “Quantum Wave Mechanics” - takes flight

Everyday waves: Sound waves

Source Detector

time

Pressure

Wavelength ~ 30cmat 1000Hz frequency

Waves can add (constructive interference)

or cancel (destructive interference)

=

=

Louder

Silent

Interference – you can hear it!

You can see interference too.

Laser

Light intensity

Light interference: Young’s double slit experiment

Wavelength

Electromagnetic waves

How about a double slit experiment for particles (atoms)?

Beam of particles

Particle Detector

How about a double slit experiment for particles (atoms)?

Beam of particles

Particle Detector

Distribution is built up from

single particle detections

How about a double slit experiment for particles (atoms)?

Beam of particlesSorry!

How about a double slit experiment for particles (atoms)?

Beam of particles

Intensity(both slits) =I1+I2

Double slit experiment for particles

Interference!!!!

electrons atoms

HitachiCarnal, Mlynek 1991

If only one particle at a time passes through

the interferometer …..

an interference pattern still builds up!!!!

“click”

Intensity pattern shows upAfter many particles detected

So what’s interfering?

LouisdeBroglie

= de Broglie wavelength

h = Planck’s constant (tiny)

m = mass

v = particle velocity

McEvoy & Zarate

h

mv

Schrödinger’s Equationfor quantum wave mechanics

McEvoy & Zarate

wavefunction

x,t2 probabilityof finding particleat position xat time t.

Particle interferometry with ever bigger, more complex objects!

• (Photons) 0• Electrons – 1950’s 0.0005• Neutrons 1975 1• Atoms 1991 10-100• Buckyballs and biomolecules 2003 >1000

C44H30N4 C60F48

h

mv

Mass / proton mass

de Broglie wavelength

Cold - the quantum frontier!

h

mvde Broglie wavelength

Temperature(random jiggling)

Thermal velocity

de Broglie wavelength

hot fastcold slow

Gas

BIG!

How cold is cold?

Thermal velocity

de Broglie wvlen. (microns)

Temperature

Florida

Air liquifies

Triton

0 -460

100 -269

200 -99

300 +81

Absolute zero – all motion stops

Record low (Antartica)

Michigan winter

Outer space (3K)

Absolute (Kelvin)

Fahrenheit (degrees)

Temp.

300 K 300m/s 1x10-5

300 K 30cm/s 0.01300 nK 1cm/s 1

1nK=0.000 000 001 K

Rubidium atom

virus

E-coli

Lasers zap, burn, cut

How do they COOL atoms????

Pushing atoms with light

Rb

Acceleration 100 000 g’s!!!!

It’s a bit harder than that …..An atom only absorbs specific colors.

(explained by quantum theory).

The laser for Rubidium atoms is a deep red. “Lowest A”

Atom is reallyspecific!!!A single key ona 26 million keypiano!!!!

Problem: How can we stop the fast atoms without speeding up the slow ones in a gas?

Solution: Doppler effect “The color the atom absorbs depends on its velocity!”

Atom moving towards the laser scatters photons

Stopped atom doesn’t scatter

Laser molasses

APPLET

I. Laser cooling atoms

Lasers

BEC intro II

JILA Mark III

JILA Mark III

~1 billion atoms10-100uK

Atom Interferometry (AI):

Light interferometersWave interference can be used to measure

(changes in) path length difference:

mirror mirror

Beam

splitter

Detector

LIGO pict

LIGO Gravitational wave detectorHanford WA

4km

A really BIG light interferometer!

de Broglie Wave Interference

Neutron interference

MICHIGAN 1975

= h/mv

= de Broglie wavelength

Particle wavepacket

Atoms (v~1m/s):

Compare with light

waves:

Shorter wavelength a more sensitive ruler!

Atom Interferometer Force Sensors

Gravity/Accelerations

gravity

LONGER de Broglie wavelength

As atom climbs gravitational potential, velocity decreases and wavelength increases

(Rotations also sensed)

The quantum mechanical wave-like properties of atoms are used to sense inertial forces.

SHORTER de Brogliewavelength

Gravimetry

MASSIVEBLOB

Gravitational force ~ mass

(distance)2

Example: Light-Pulse AI Gravity Gradiometer

Mirror

Atoms

Atoms

L a s

e r

B

e a

m

Gradient measurements: Distinguish gravity induced accelerations from those due to platform motion.

– Simultaneously measure g at two locations with atom interferometer accelerometers

– Difference acceleration signal contains gradient information

G. McGuirk, M. Kasevich

Laboratory validation: Mass Detection

Pb bricks

Lower accelerometer

Sample number (1 sample/sec)

Gra

dien

t (ar

b. u

nits

)

Modulated acceleration signal due to 8 lead bricks near lower accelerometer.

Green o,+: upper/lower accelerometer outputs

Blue: Gradient signal

Successful laboratory demonstration of mass anomaly detection capabilities

G. McGuirk, M. Kasevich

Applications

• SSN/SSBN Navigation - Gravity assisted navigation (currently in use on subs, but need better)

• Underground structure detection (a.k.a. bunker detection)

• Oil and mineral exploration (e.g. kimberlite pipes in Utah –diamonds come from kimberlite, or salt domes in the Gulf of Mexico: oil)

• Space-based studies of Earth’s gravity field

LM UGM

II. Quantum Tornadoes Near Absolute Zero

Courtesy NOAA

Plus ….what kind of thermometer measures the coldest places in the universe anyways?

Hot cloud

Images of clouds

How to make a thermometer for cold atoms

Let the gas expand

Cold cloud