Transcript What is Bose Einstein Condensation?

“When freezing cold is not cold
enough - new forms of matter close
to absolute zero temperature”
Wolfgang Ketterle
Massachusetts Institute of Technology
MIT-Harvard Center for Ultracold Atoms
9/2/09
Meridian Lecture
Space Telescope Science Institute
Baltimore
Quantum Gases
The coldest matter
in the universe
What is temperature?
A measure of energy
One form of energy is motion
(kinetic energy).
Cold particles
move slowly
Hot particles
are fast
What is the lowest
temperatures possible?
Zero degree Kelvin
(-273 degrees Celsius,
-460 degrees Fahrenheit)
is the zero point
for energy
The highest temperature
is infinite
(In principle it is possible for particles to have
arbitrarily high kinetic energies –
until they become so heavy (due to E=mc2)
that they from a black hole – at the
Planck temperature of 1032 K)
What is the difference
in temperature between
summer and winter?
20 %
How cold is
interstellar space?
3K
How cold is it
in our laboratories?
Nanokelvin:
A billion times
colder than interstellar
space
Why can you make
new discoveries
at cold temperatures?
What happens to atoms
at low temperatures?
They slow down
600 mph (300 m/sec)
1 cm/sec
They march in lockstep
Matter made of waves!
Population per energy state
What is Bose Einstein Condensation?
Bose-Einstein distribution
T=Tc
Energy
Population per energy state
What is Bose Einstein Condensation?
T<Tc
Condensate!
Bose-Einstein distribution
Energy
Population per energy state
What is Bose Einstein Condensation?
T<Tc
Condensate!
Bose-Einstein distribution
Energy
Ordinary light
Photons/atoms moving randomly
Laser light
Photons/atoms are one big wave
* 1925
Gases (Atoms and Molecules)
1
n( ) 
e
(    ) k BT
1
1
e
 k BT
1
Black-Body Radiation
“Photons”
Max Planck
The cooling methods
• Laser cooling
• Evaporative cooling
Hot atoms
Hot atoms
Laser beams
Hot atoms
Fluorescence
Laser beams
Fluorescence
Laser beams
If the emitted radiation is blue shifted
(e.g. by the Doppler effect) ….
Cold atoms: 10 – 100 K
Fluorescence
Laser beams
Chu, Cohen-Tannoudji, Phillips, Pritchard, Ashkin, Lethokov, Hänsch,
Schawlow, Wineland …
Laser cooling
2.5 cm
Evaporative
cooling
Phillips et al. (1985)
Pritchard et al. (1987)
One challenge …
experimental complexity
Sodium laser cooling experiment (1992)
Sodium BEC I experiment (2001)
Dan Kleppner
Tom Greytak
Dave Pritchard
I.I. Rabi
PhD
Norman Ramsey
PhD
Dan Kleppner
PhD
PhD
PhD
Dave Pritchard
Postdoc
Bill Phillips
PhD
Eric Cornell
Undergraduate
Postdoc
Wolfgang Ketterle
Randy
Hulet
Carl Wieman
Key factors for success:
• Funding
• Technical infrastructure
• Excellent collaborators
• Tradition and mentors
How do we show that
the Bose-Einstein
condensate has very
low energy?
The condensate
• a puff of gas
• 100,000 thinner than air
• size comparable to the
thickness of a hair
• magnetically suspended in
an ultrahigh vacuum chamber
How to measure temperature?
Gas
Effusive atomic beam
Kinetic energy mv2/2 = kBT/2
How to measure temperature?
Gas
Effusive atomic beam
Kinetic energy mv2/2 = kBT/2
CCD
CCD
Ballistic expansion: direct information about
velocity distribution
CCD
Ballistic expansion: direct information about
velocity distribution
Absorption image: shadow of atoms
The shadow of a cloud of bosons
as the temperature is decreased
(Ballistic expansion for a fixed time-of-flight)
Temperature is linearly related to the rf frequency
which controls the evaporation
Distribution of the times when data images were taken
during one year between 2/98-1/99
Key factors for success:
• Some funding
• Technical infrastructure
• Excellent collaborators
• Tradition and mentors
Key factors for success:
• Some funding
• Technical infrastructure
• Excellent collaborators
• Tradition and mentors
• Physical endurance
How can you prove that atoms march in lockstep?
Atoms are one single wave
Atoms are coherent
One paint ball on a white wall
Two
Paint does not show wave properties
One laser beam on a white wall
Light shows wave properties
One laser beam on a white wall
Two
Fringe pattern:
Bright-dark-bright-dark
Light shows wave properties
Two condensates ...
50 m
Interference of two Bose-Einstein condensates
Andrews, Townsend, Miesner, Durfee, Kurn, Ketterle, Science 275, 589 (1997)
How do we show that the
gas is superfluid?
Rigid body:
Vortices in nature
Spinning a Bose-Einstein condensate
The rotating bucket experiment with a superfluid gas
100,000 thinner than air
Rotating
green laser beams
Two-component vortex
Boulder, 1999
Single-component vortices
Paris, 1999
Boulder, 2000
MIT 2001
Oxford 2001
J. Abo-Shaeer, C. Raman, J.M. Vogels,
W.Ketterle, Science, 4/20/2001
Current Research
BEC on a microchip
Loading sodium BECs into atom chips
with optical tweezers
44 cm
BEC
arrival
BEC
production
T.L.Gustavson, A.P.Chikkatur, A.E.Leanhardt,
A.Görlitz, S.Gupta, D.E.Pritchard, W. Ketterle,
Phys. Rev. Lett. 88, 020401 (2002).
Atom chip with waveguides
Splitting of condensates
1mm
One trapped 15ms
condensate Expansion
Two condensates
Splitting of condensates
1mm
Trapped
15ms
expansion
Two condensates
Splitting of condensates
Two condensates
Y. Shin, C. Sanner, G.-B. Jo, T. A. Pasquini, M. Saba, W. Ketterle, D. E. Pritchard, M.
Vengalattore, and M. Prentiss: Phys. Rev. A 72, 021604(R) (2005).
Splitting of condensates
Two condensates
Atom interferometry:
The goal:
Matter wave sensors
Use ultracold atoms to sense
Rotation
 Navigation
Gravitation  Geological exploration
Current Research
Cold molecules
Cold fermions
Can electrons form a Bose-Einstein condensate
and become superfluid (superconducting)?
Two kinds of particles
• Bosons: Particles with an even number of protons, neutrons
and electrons
• Fermions: odd number of constituents
Only bosons can Bose-Einstein condense!
Can electrons form a Bose-Einstein condensate
and become superfluid (superconducting)?
Two kinds of particles
• Bosons: Particles with an even number of protons, neutrons
and electrons
• Fermions: odd number of constituents
Only bosons can Bose-Einstein condense!
How can electrons (fermions) condense?
They have to form pairs!
Can we learn something about
superconductivity
of electrons from cold atoms?
Yes, by studying pairing and superfluidity
of atoms with an odd number of protons,
electrons and neutrons
BEC of Fermion
Pairs (“Molecules”)
These days: Up to 10 million
condensed molecules
Boulder
Innsbruck
MIT
Paris
Rice, Duke
Nov ‘03
Nov ‘03, Jan ’04
Nov ’03
March ’04
M.W. Zwierlein, C. A. Stan, C. H. Schunck,
S.M. F. Raupach, S. Gupta, Z. Hadzibabic,
W.K., Phys. Rev. Lett. 91, 250401 (2003)
Gallery of superfluid gases
Atomic Bose-Einstein
condensate (sodium)
Molecular Bose-Einstein
condensate (lithium 6Li2)
Pairs of fermionic
atoms (lithium-6)
Ultracold atoms
A “toolbox” for designer matter
Normal matter
• Tightly packed atoms
• Complicated Interactions
• Impurities and defects
Ultracold atoms
A “toolbox” for designer matter
Matter of ultracold atoms
• 100 million times lower density
• Interactions understood and controlled
• no impurities
• exact calculations possible
Need 100 million
times colder
temperatures