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