Title “When freezing cold is not cold enough - new forms of matter close to absolute zero...
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“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
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Transcript of Title “When freezing cold is not cold enough - new forms of matter close to absolute zero...
“When freezing cold is not cold enough - new forms of matter close
to absolute zero temperature”Wolfgang Ketterle
Massachusetts Institute of TechnologyMIT-Harvard Center for Ultracold Atoms
9/2/09Meridian Lecture
Space Telescope Science InstituteBaltimore
Quantum Gases
The coldest matterin the universe
What is temperature?
A measure of energy
One form of energy is motion(kinetic energy).
Cold particles move slowly
Hot particlesare 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 differencein temperature between
summer and winter?
20 %
How cold is interstellar space?
3 K
How cold is itin our laboratories?
Nanokelvin:A billion times
colder than interstellarspace
Why can you makenew discoveries
at cold temperatures?
What happens to atomsat low temperatures?
They slow down600 mph (300 m/sec) 1 cm/sec
They march in lockstep
Matter made of waves!
Energy
Pop
ulat
ion
per
ener
gy s
tate
What is Bose Einstein Condensation?
T=Tc
Bose-Einstein distribution
Energy
Pop
ulat
ion
per
ener
gy s
tate
What is Bose Einstein Condensation?
Bose-Einstein distribution
T<Tc
Condensate!
Energy
Pop
ulat
ion
per
ener
gy s
tate
What is Bose Einstein Condensation?
Bose-Einstein distribution
T<Tc
Condensate!
Laser lightOrdinary light
Photons/atoms moving randomly Photons/atoms are one big wave
* 1925
)(n1
1)( TkBe
1
1
TkBe
Max Planck
Black-Body Radiation“Photons”
Gases (Atoms and Molecules)
The cooling methods
• Laser cooling• Evaporative cooling
Hot atoms
Hot atoms
Laser beams
Hot atoms
Laser beams
Fluorescence
Laser beams
Fluorescence
If the emitted radiation is blue shifted (e.g. by the Doppler effect) ….
Cold atoms: 10 – 100 K
Laser beams
Fluorescence
Chu, Cohen-Tannoudji, Phillips, Pritchard, Ashkin, Lethokov, Hänsch, Schawlow, Wineland …
2.5 cm
Laser cooling
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
Dan Kleppner
Dave Pritchard
Eric Cornell Carl WiemanWolfgang Ketterle
Bill PhillipsPhD
PhD
Postdoc
Under-graduate
PhD
RandyHulet
PhD
Norman Ramsey
PhD
I.I. Rabi
PhD
Postdoc
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?
Kinetic energy mv2/2 = kBT/2
Gas Effusive atomic beam
How to measure temperature?
Kinetic energy mv2/2 = kBT/2
Gas Effusive atomic beam
CCD
CCD
Ballistic expansion: direct information about velocity distribution
CCD
Absorption image: shadow of atoms
Ballistic expansion: direct information about velocity distribution
The shadow of a cloud of bosonsas 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 takenduring 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 waveAtoms are coherent
One paint ball on a white wallTwo
Paint does not show wave properties
One laser beam on a white wall
Light shows wave properties
One laser beam on a white wallTwo
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
Rotatinggreen laser beams
The rotating bucket experiment with a superfluid gas 100,000 thinner than air
Two-component vortex Boulder, 1999Single-component vortices Paris, 1999 Boulder, 2000 MIT 2001 Oxford 2001
J. Abo-Shaeer, C. Raman, J.M. Vogels,W.Ketterle, Science, 4/20/2001
BEC on a microchip
Current Research
Loading sodium BECs into atom chipswith optical tweezers
BECproductionBEC
arrival
44 cm
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
15ms Expansion
Two condensates
1mm
One trappedcondensate
Trapped 15ms expansion
1mm
Two condensates
Splitting of condensates
Two condensates
Splitting of 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).
Two condensates
Splitting of condensates
The goal:Atom interferometry:Matter wave sensors
Use ultracold atoms to sense
Rotation NavigationGravitation Geological exploration
Cold moleculesCold fermions
Current Research
Can electrons form a Bose-Einstein condensateand 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 condensateand 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 aboutsuperconductivity
of electrons from cold atoms?
Yes, by studying pairing and superfluidity of atoms with an odd number of protons,
electrons and neutrons
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)
BEC of Fermion Pairs (“Molecules”)
Boulder Nov ‘03Innsbruck Nov ‘03, Jan ’04MIT Nov ’03Paris March ’04Rice, Duke
These days: Up to 10 million condensed molecules
Atomic Bose-Einsteincondensate (sodium)
Molecular Bose-Einsteincondensate (lithium 6Li2)
Pairs of fermionicatoms (lithium-6)
Gallery of superfluid gases
Ultracold atomsA “toolbox” for designer matter
Normal matter• Tightly packed atoms• Complicated Interactions• Impurities and defects
Matter of ultracold atoms• 100 million times lower density• Interactions understood and controlled• no impurities• exact calculations possible
Ultracold atomsA “toolbox” for designer matter
Need 100 million times colder temperatures
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