Transcript Quantum wierdness at the lowest temperatures in the Universe

Bose-Einstein condensation;
Quantum weirdness at the lowest
temperature in the universe
Part I. Introduction to quantum physics
Part II. (1924-95) Making Bose-Einstein Condensation in a gas.
BEC- a new form of matter predicted by Einstein in 1924 and first
created in 1995 by our group.
Part III. An example of research with BEC.
Spread clickers throughout the room, no two clickers next to each
other. PRESS “ON/OFF” BUTTON ON CLICKER. Light appears
$$ (NSF, ONR, NIST)
clicker data gathering
CQ1. Age?
A. less than 10 years old
C. 15-18
D. 18-23
B. 10-14
E. 23- 99 yrs old
CQ2. Most advanced physics classes taken?
a. none
b. physics 11 or 12
c. a college or university physics class
d. college or university quantum physics class
e. graduate school physics class
anyone who answered e. (graduate school physics) ,
give clicker to someone not in category e.
Bose-Einstein condensation;
Quantum weirdness at the lowest
temperature in the universe
Part I. Basics of quantum physics
A. Location of particle as probability wave
B. Particles only allowed to have particular energies
C. Energies of electrons in atoms
A. Location of particle as probability wave
Shoot electron at screen-- see where it is detected.
Repeat with new electron, everything
else as exactly the same as possible.
CQ3. Where on the screen will it be
detected?
(discuss with neighbors, then vote)
a. anywhere on screen.
b. anywhere except where first one hit.
c. at same spot as where first one hit
d. in center of the screen
e. some other answer
ans. a anywhere on screen
Send electron through double slit.
CQ5. Where will it be detected on the
screen?
(super submicroscopic machine!!)
a. just like before, anywhere in broad
region.
b. anywhere in two broad regions-- one
on each side with gap in middle.
c. somewhere in one of a few bands, but
not in spaces between those bands
d. will not be screen at all, because is
too wide to get through slits.
send some electrons
CQ5. Send electron through double slit. Where will it be detected on
the screen?
a. just like before, anywhere in broad region.
b. anywhere in two broad regions-- one on each side with gap in
middle.
c. somewhere in one of a few bands, but not in spaces between
those bands
d. will not be screen at all, because is too wide to get through slits.
wave interference sim
Electrons interfere like waves!
Where waves add, lots of electrons
detected, waves cancel- none.
wave interference sim
waves cancel
waves add- bigger
wave
atoms same as electrons-- just slower time scale
smaller spacing between waves.
CQ6. Why not see normal objects with location fuzzy-- described
by probability wave, interference etc.?
a. they are moving around too fast so don’t see fuzziness.
b. are spread out, but over too small a distance to see.
c. this whole explanation is crazy and wrong.
d. because fuzziness only can be seen if objects are very hot.
ans. b They are spread out, but over very small distance.
How small depends on weight and temperature of object.
room temp
electron spread (fuzzed) out over 0.000 000 007 m
atom is spread over 0.000 000 000 02 m
hockey puck-- spread over
0.000 000 000 000 000 000 000 02 m
First important idea of quantum physics
Location of object described by probability wave.
When detect, see it at one spot, but identical object will
be detected in different place-- just probability.
B. Particles only allowed to have particular energies
Where particle can be found is described by probability wave
What does that mean when particles (electrons, atoms)
in a container?
Waves have to just fit.
Potential well sim.
2nd lowest energy
lowest energy particle
What will wave look like for next level?
higher energy waves have more wiggles
2nd Important Idea of Quantum Physics
Particles in container can only have certain energies
-- correspond to where wave just fits into container.
Cannot exist with other energies! gap between energies
Energy is “quantized”  “quantum physics”
What does the gap between energy levels depend on?
CQ7. What happens to energy gap if make container wider?
a. gets larger (allowed energies get farther apart).
b. stays the same.
c. gets smaller (allowed energies get closer together)
check with sim
ans. c. levels get closer together
CQ8. Why if we look at cars, people, M&Ms in jar, etc., they appear to
have any energy/speed they want (no gaps)?
a. quantum physics only applies to electrons
b. quantum physics applies to things that are too small to see, like
electrons or atoms, but not to normal sized objects.
c. for human size scale objects, energy levels are there, but too close
together to see gaps.
d. hockey pucks, people, etc are jumping around between different
energy levels so fast, we can’t see or measure the gaps.
ans. c.
C. Energies of electrons in atoms
Electron held in an atom is in very small container.
 Bigger energy gaps. Slightly different for each atom.
Can only absorb exact amount of energy needed to jump
to higher level (color of light)
Can only give off exact amount
of energy (light of particular color)
needed to jump to lower level.
Key ideas of quantum physics
1. Location of particle fuzzy-- defined by probability wave.
2. Particle can only have certain energies in container,
higher energy more wiggles in probability wave.
( wiggles farther apart when energy lower )
3. Electron stuck in atom-- can only have certain energy levels.
Will only jump up to higher energy if exactly right color light
(right energy) hits it.
Jumps back down and gives off exactly energy difference
(particular color light)
Part II. (1924-95) Making Bose-Einstein Condensation in a gas.
BEC- a new form of matter predicted by Einstein in 1924 and first
created in 1995 by our group.
JILA BEC Effort Eric Cornell, Carl Wieman 1990Anderson, Ensher, Jin, Hall, Matthews, Myatt, Monroe, Claussen,
Roberts, Cornish, Haljan, Donley, Thompson, Papp, Zirbel,
Lewandowski, Harber, Coddington, Engels, McGuirk, Hodby,...
temperature applet
Absolute
(Kelvin)
300
earth
250
200
150
100
50
Absolute zero! 0
All motion stops
-273 oC
CQ8. Where is the coldest place in the
universe.
a. Boulder Colorado
b. Antarctica
c. recently demoted planet Pluto
d. halfway between sun and next
closest star
e. intergalactic space (between
galaxies)
Absolute
(Kelvin)
300
earth
Room Temp
Water freezes
250
200
Dry Ice
150
100
Air freezes
50
Absolute zero! 0
All motion stops
-273 oC
Deep space, 3 K
BEC at .000 000 1o
above Absolute zero
Boulder Colorado
CSIU
Cold atoms
Hot atoms
A. E. 1924
(more than 10 millionths
of degree above abs. zero)
colder = lower energy
= ?? spacing
between prob.
wave wiggles?
a. smaller
b. larger
energy levels too close
together to detect
BEC
1 cm bowl
100 billionths of a
degree
"superatom" --single quantum wave
evacuated
glass cell
coils of wire
diode lasers
(cheap)
B coils
2.5 cm
JILA BEC #2
(#1 at Smithsonian)
2 in.
Grad students Neil Claussen, Sarah Thompson, postdoc Liz Donley
working on BEC experiment.
Getting atoms cold- step 1
Rb
Pushing atoms with light
Why does sunlight heat you up, but
laser light cools these atoms down?
gas atoms can absorb and reradiate light
a. that is whatever the color of light that shines on them
b. that is bluer (higher energy) light than the first energy gap
c. that is at only at particular precise frequencies or colors.
ans. c.
if light just the right color…
electrons absorb light jump to higher energy level
jump back down, give off light
laser cooling applet
optical molasses applet
magnetic trapping applet
evaporative cooling applet
www.colorado.edu/physics/2000/
BEC section
Shadow “snapshot” of BEC
CCD array
(TV camera)
Shadow images of clouds
1
2
CQ. Which cloud is hotter?
A. 1 is hotter than 2.
B. 2 is hotter than 1.
C. Impossible to tell just from shadow picture
Shadow images of clouds
Hot cloud
Cold cloud
BEC!
JILA-June 1995
50 billionths
~ 200 billionths
400 billionths
of degree
0.2 mm
False color images of cloud
Cold atoms
Hot atoms
(microKelvins)
A. E. 1924
Bosons
lowest level smallest
width- set by uncertainty principle
Quantum physics on “human” size scale
Control and Observe
Putting one condensate on
top of another
about width of human hair
Fringes formed with two overlapping
condensates- probability waves
interfering!
(NIST Gaithersburg atom cooling group
courtesy S. Rolston)
-
Where BEC now (post June ‘95)?
New regime of physicsdirectly observe and manipulate quantum wave function
~ 250+ working experiments, many atoms (87Rb, Na, Li, H, 85Rb, He*,K, Cs)
>1000 scientists
countless theoristsmany thousands of papers
•Measured and predicted all sorts of
novel properties.
•New ways to study, make and
manipulate.
•Potential applications.
Stockholm Sweden, Dec. 10, 2001
Part III. Some research with BEC
New material. Explore behavior, find occasional surprises,
understand  new understanding of nature.
Controlling self-interactions with 85Rubidium BEC
Roberts, Claussen, Donley, Thompson, CEW
repulsive
(87RB,
Na), a > 0
attractive (Li, 85Rb), a < 0
(unstable if N large, Nmax1/a)
in 85 Rb have experimental knob to adjust from large
repulsive to nothing to large attractive!
Magnetic field
3 billionths of a degree!
Plunging into the unknown– interaction attractive
Lots of theory, varied wildly.
Little data
?
1. Make BEC
magnetic field
where repulsive
2. Switch to attractive.
What happens?
(how do quantum wavefunctions die?)
Start: 10,000 atom BEC
Collapse
time
then…
x3
Explosion !!
10,000 atoms
like supernova:
•collapse
•explosion… (x 10-73 )
•cold remnant
0.2ms
0.7ms
“Bosenova”
0.1 mm
1.8ms
2.3ms
What is the physics of
explosion???
Why remnant remains?
progress…
4.3ms
1500 atom explosion
T ~ 200 nK
4.8ms
X3
source of energy of Bosenova--chemical
A New Type of Chemistry-changing magnetic field just right turns atoms in
BEC into unusual Rb2 "molecules".
•10,000 times larger than normal molecules
•new formation processes
learned something new about nature--being studied
and used for all sorts of research.
Quantum physics interactive simulations
(and many many more for learning lots of other physics)
at PHET.Colorado.edu
Laser cooling, magnetic trapping and evaporative cooling
simulations (and more)
www.colorado.edu/physics/2000/
end
see BEC section
(what is it good for?)
I. Measure and understand properties.
New area of quantum world to explore–
turning BEC atoms into strange new sort of molecules
II. Uses (??)....
5-20 years (“laser-like atoms”)
a. Ultrasensitive detectors (time, gravity, rotation).
making a quantum computer(?).
b. Making tiny stuff--putting atoms exactly where want them
simulations shown (and more)
www.colorado.edu/physics/2000/
see BEC section
interactive simulations for quantum and lots of other physics
PHET.Colorado.edu