- 86 Views
- Uploaded on
- Presentation posted in: General

Title

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

“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 Institute

Baltimore

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 betweensummer and winter?

20 %

How cold is interstellar space?

3 K

How cold is itin our laboratories?

Nanokelvin:A billion timescolder than interstellar

space

Why can you makenew discoveriesat cold temperatures?

They slow down

600 mph (300 m/sec)

1 cm/sec

What happens to atomsat low temperatures?

They march in lockstep

Matter made of waves!

What is Bose Einstein Condensation?

Population per energy state

Bose-Einstein distribution

T=Tc

Energy

T<Tc

Condensate!

What is Bose Einstein Condensation?

Population per energy state

Bose-Einstein distribution

Energy

What is Bose Einstein Condensation?

T<Tc

Condensate!

Population per energy state

Bose-Einstein distribution

Energy

Photons/atoms are one big wave

Photons/atoms moving randomly

Ordinary light

Laser light

* 1925

Gases (Atoms and Molecules)

Black-Body Radiation

“Photons”

Max Planck

The cooling methods

- Laser cooling
- Evaporative cooling

Hot atoms

Laser beams

Hot atoms

Fluorescence

Laser beams

Hot atoms

Laser beams

Fluorescence

If the emitted radiation is blue shifted

(e.g. by the Doppler effect) ….

Laser beams

Cold atoms: 10 – 100 K

Fluorescence

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)

Dave Pritchard

Dan Kleppner

Tom Greytak

I.I. Rabi

PhD

Norman Ramsey

PhD

Dan Kleppner

PhD

PhD

PhD

Under-

graduate

Dave Pritchard

Postdoc

RandyHulet

Bill Phillips

Postdoc

PhD

Eric Cornell

Wolfgang Ketterle

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

Effusive atomic beam

Gas

How to measure temperature?

Kinetic energy mv2/2 = kBT/2

Effusive atomic beam

Gas

How to measure temperature?

Kinetic energy mv2/2 = kBT/2

CCD

CCD

Ballistic expansion:direct information about velocity distribution

Absorption image: shadow of atoms

CCD

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

Two

One paint ball on a white wall

Paint does not show wave properties

One laser beam on a white wall

Light shows wave properties

Two

One laser beam on a white wall

Fringe pattern:

Bright-dark-bright-dark

Light shows wave properties

Two condensates ...

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 vortexBoulder, 1999Single-component vorticesParis, 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 chipswith optical tweezers

44 cm

Atom chip with waveguides

BECproduction

BECarrival

T.L.Gustavson, A.P.Chikkatur, A.E.Leanhardt, A.Görlitz, S.Gupta, D.E.Pritchard, W. Ketterle, Phys. Rev. Lett. 88, 020401 (2002).

Splitting of condensates

1mm

One trappedcondensate

15ms

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:

Matter wave sensors

The goal:

Use ultracold atoms to sense

Rotation Navigation

Gravitation Geological exploration

Current Research

Cold molecules

Cold fermions

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 aboutsuperconductivityof 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 Nov ‘03Innsbruck Nov ‘03, Jan ’04

MIT Nov ’03Paris March ’04

Rice, Duke

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-Einsteincondensate (sodium)

Molecular Bose-Einsteincondensate (lithium 6Li2)

Pairs of fermionicatoms (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