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Title. “New forms of quantum matter near absolute zero temperature” Wolfgang Ketterle Massachusetts Institute of Technology MIT-Harvard Center for Ultracold Atoms 5/23/06 NASA workshop Airlie Center. Title. The ongoing revolution in atomic physics …. Title.

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title
Title

“New forms of quantum matter near absolute zero temperature”

Wolfgang Ketterle

Massachusetts Institute of TechnologyMIT-Harvard Center for Ultracold Atoms

5/23/06

NASA workshop

Airlie Center

title1
Title

The ongoing revolution in atomic physics …

title2
Title

Enabling technology:Nanokelvin temperatures

the concepts
The concepts

The cooling methods

  • Laser cooling
  • Evaporative cooling
height of atmosphere
Height of atmosphere

e-(106)

300 mK

h=1 cm

Potential (gravitational) energy mgh = kBT/2

(g: gravitational acceleration)

How to measure temperature

Height of the atmosphere

1 nK

h= 30 nm

300 K

h=10 km

In thermal equilibrium: Potential energy ~ kinetic energy

slide8

Lowest temperature ever achieved: 450 picokelvin

1.05 nK

1 cm

780 pK

Trapping a sodium BECwith a single coil

450 pK

A.E. Leanhardt, T.A. Pasquini, M. Saba, A. Schirotzek, Y. Shin, D. Kielpinski, D.E. Pritchard, and W. Ketterle, Science 301, 1513 (2003).

Temperature measurement by imaging the size of the trapped cloud

precision measurements
Precision measurements

Precision measurements with

Bose-Einstein condensates ...

We have to get rid of perturbing fields …

  • Gravity
  • Magnetic fields
slide10

What distinguishes nanokelvin?

  • Physics
    • BEC Phase transition Quantum reflection
    • Interactions
    • Ease of Manipulation
bec at jila and mit
BEC at JILA and MIT

BEC @ JILA, June ‘95(Rubidium)

BEC @ MIT, Sept. ‘95 (Sodium)

quantum reflection of ultracold atoms
Quantum Reflection of Ultracold Atoms

T.A. Pasquini, Y. Shin, C. Sanner, M. Saba, A. Schirotzek,

D.E. Pritchard, W.K.

  • Phys. Rev. Lett. 93, 223201 (2004)
  • Preprint (2006)
slide13

Sodium BEC

Silicon surface

quantum reflection from nanopillars
Quantum Reflection from Nanopillars

Solid Si surface

Reduced density Si surface

Reflection Probability

Velocity (mm/s)

1 mm/s is 1.5 nK x kB kinetic energy

slide15

What distinguishes nanokelvin?

  • Physics
    • BEC Phase transition Quantum reflection
    • Interactions
    • Ease of Manipulation
moving condensates
Moving condensates

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).

slide18

Splitting of condensates

1mm

One trappedcondensate

15ms

Expansion

Two condensates

slide19

Splitting of condensates

1mm

Trapped

15ms

expansion

Two condensates

slide20

Splitting of condensates

Two condensates

Very recent progress:

200 ms coherence time for an atom chip interferometer

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).

slide21

Splitting of condensates

Two condensates

Atom interferometry:

Matter wave sensors

The goal:

Use ultracold atoms to sense

Rotation  Navigation

Gravitation  Geological exploration

slide22

What distinguishes nanokelvin?

  • Physics
    • BEC Phase transition Quantum reflection
    • Interactions
    • Ease of Manipulation
slide23

Two of the biggest questions in condensed matter physics:

The nature of high-temperature superconductors

Quantum magnetism, spin liquids

Strongly correlated, strongly interacting systems

title3
Title

How to get strong interactions?

Pair A-B

Particle A

Particle B

title4
Title

Resonant interactions

have infinite strength

Pair A-B

Particle A

Particle B

  • Unitarity limited interactions:
  • Pairing in ultracold fermions
  • Relevant to quark-gluon plasmas
slide26

E

Free atoms

Molecule

Magnetic field

Feshbach resonance

slide27

Disclaimer: Drawing is schematic and does not distinguish nuclear and electron spin.

E

Free atoms

Molecule

Magnetic field

Feshbach resonance

slide28

Two atoms ….

E

Free atoms

Molecule

Magnetic field

Feshbach resonance

slide29

… form an unstable molecule

E

Free atoms

Molecule

Magnetic field

Feshbach resonance

slide30

… form a stable molecule

E

Free atoms

Molecule

Magnetic field

Feshbach resonance

slide31

Atoms attract each other

E

Free atoms

Molecule

Magnetic field

Feshbach resonance

slide32

Atoms repel each other

Atoms attract each other

E

Free atoms

Molecule

Magnetic field

Feshbach resonance

slide33

Atoms repel each other

Atoms attract each other

Force between atoms

Scattering length

Magnetic field

Feshbach resonance

title5
Title

Observation of High-Temperature Superfluidity in Ultracold Fermi Gases

slide35

At absolute zero temperature …

Bose-Einstein condensation

 atoms as waves

 superfluidity

Fermi sea:

 Atoms are not coherent

 No superfluidity

Bosons

Particles with an even number of

protons, neutrons and electrons

Fermions

Particles with an odd number of

protons, neutrons and electrons

slide36

Pairs of fermions

Particles with an even number of

protons, neutrons and electrons

Two kinds of fermions

Fermi sea:

 Atoms are not coherent

 No superfluidity

slide37

At absolute zero temperature …

Pairs of fermions

Particles with an even number of

protons, neutrons and electrons

Bose-Einstein condensation

 atoms as waves

 superfluidity

Two kinds of fermions

Particles with an odd number of

protons, neutrons and electrons

Fermi sea:

 Atoms are not coherent

 No superfluidity

slide38

Weak attractive interactions

Cooper pairs

larger than interatomic distance

momentum correlations

 BCS superfluidity

Two kinds of fermions

Particles with an odd number of

protons, neutrons and electrons

Fermi sea:

 Atoms are not coherent

 No superfluidity

slide39

Electron pairs

Atom pairs

Bose Einstein condensate of molecules

BCS Superconductor

slide40

Atoms attract each othera<0

Atoms repel each othera>0

Energy

Atoms

Molecules

Magnetic field

Molecules are unstable

Atoms form stable molecules

BCS-limit:

Condensation of

long-range Cooper pairs

BEC of Molecules:

Condensation of

tightly bound fermion pairs

slide41

Atom pairs

Bose Einstein condensate of molecules

BCS superfluid

slide42

BCS superfluid

Molecular BEC

slide43

Magnetic field

BCS superfluid

Molecular BEC

slide44

Crossover superfluid

BCS superfluid

Molecular BEC

slide45

Fermi energy

Fermi temperature

(density)2/3

high Tc superfluid

0.3

High-temperature superfluidity at 100 nK?

Transition temperature

Binding energy of pairs

10-5 … 10-4normal superconductors

10-3superfluid 3He

10-2high Tc superconductors

Scaled to the density of electrons in a solid:Superconductivity far above room temperature!

slide46

Preparation of an interacting Fermi system in Lithium-6

Optical trapping @ 1064 nm

naxial = 10-20 Hznradial= 50–200 Hz

Etrap = 0.5 - 5 mK

States |1> and |2> correspond to

|> and |>

title6
Title

How to show that these gases are superfluid?

quantized circulation
Quantized circulation

Quantization: Integer number of matter waves on a circle

slide51

Spinning a strongly interacting Fermi gas

Container is an optical trapat high bias field!

Makes life hard …..

Have to fight against:

  • Imperfections of the beam
  • Anisotropy
  • Anharmonicity
  • Stray magnetic field gradients
  • Gravity
  • etc…
slide52

Vortices in the BEC-BCS Crossover

Vortex lattices in the BEC-BCS crossover

This establishes phase coherence and superfluidity

in gases of molecules and of fermionic atoms

  • Astrophysical significance:
  • Superfluidity of neutron in neutron stars
  • Pulsar glitches

M.W. Zwierlein, J.R. Abo-Shaeer, A. Schirotzek, C.H. Schunck, W. Ketterle,

Nature 435, 1047-1051 (2005)

slide53

Gallery of superfluid gases

Atomic Bose-Einsteincondensate (sodium)

Molecular Bose-Einsteincondensate (lithium 6Li2)

Pairs of fermionicatoms (lithium-6)

slide54

Fermionic Superfluidity withImbalanced Spin Populations

  • Astrophysical significance:
  • Superfluidity of quarks in neutron stars
slide56

BCS Pairing of Fermions

Pairing costs kinetic energy, but there is gain in potentialenergy (attractive interaction between fermions)

m2

m1

Pairing energy D

Energy

slide57

BCS Pairing of Fermions

Unequal Fermi energies (non-interacting)

(example: Apply magnetic field to a normal conductor)

m1

m2

Energy

slide58

BCS Pairing of Fermions

Interacting case, fixed particle number:

Phase separation! (Bedaque, Caldas, Rupak 2003)

Breakdown of the BCS state

when Dm1 –m2

Clogston 1962

Superfluid gapis now smaller

m1

m2

Energy

N

S

N

slide59

Breached

Pair State

FFLO/

LOFF-State

PhaseSeparation

Distorted Fermi

Surface

Recent theory (>=2005): Carlson, Reddy, Cohen, Sedriakan,Mur-Petit, Polls, Müther, Castorina, Grasso, Oertel, Urban, Zappalà,Pao, Wu, Yip, Sheehy, Radzihovsky, Son, Stephanov, Yang,Sachdev, Pieri, Strinati, Yi, Duan, He, Jin, Zhuang, Caldas, Chevy

slide60

Fermionic Superfluidity with Imbalanced Spin Populations

BEC-Side

1/kFa = 0.2

|1>

|2>

0%

6%

12%

22%

30%

56%

90%

94%

Population Imbalance: d = (N2-N1)/(N2+N1)

BCS-Side

1/kFa = -0.15

|1>

|2>

0%

-2%

-16%

-32%

-48%

-58%

-74%

-100%

slide61

Momentum distribution after magnetic field sweep to the BEC side

|2>

|1>

Increase population imbalance

slide62

The Window of Superfluidity

1/kFa

BEC

0.11

0

Decreasing Interaction

Condensate Fraction

– 0.27

– 0.44

BCS

Population Imbalance

Superfluidity is robust in the strongly interacting regime!

M.W. Zwierlein, A. Schirotzek, C.H. Schunck, W. Ketterle,

Science 311, 492 (2006), published online on Science Express 21 December 2005

slide63

Phase Diagram for Unequal Mixtures

Normal

EKin = 310 nK

350 nK

Critical Population Imbalance

400 nK

Superfluid

430 nK

D

BEC

BCS

Breakdown: Critical mismatch in Fermi energies DEF Gap D

slide64

What is the nature of

the superfluid state?

m1

m2

Energy

N

S

N

slide65

Phase Contrast Imaging

  • Imaging beam red-detuned for |1>,
  • blue-detuned for |2>
  • Optical signal of phase-contrast imaging directly measures density difference Dn=n2-n1

|3>

n2

|2>

80 MHz

|1>

n1

|1>

|2>

Equalmixture

Li linewidth: G= 6 MHz

In-trap images

direct imaging of the density difference
Direct imaging of the density difference

-50%

-37%

-30%

-24%

0%

20%

30%

40%

50%

Population imbalance

The shell structure is a hint of the phase separation.

reconstruction of 3d density profile
Reconstruction of 3D density profile

d=0.6

Only assumption: cylindrical symmetry

Phase Separation !!

slide68

a

DB

Atomic physics “knobs” to control many-body physics

Density 1011 to 1015 cm-3

Temperature 500 pK to 1 mK

Interactions: scattering length a -  to +

Choice of hyperfine state(s): |, |; spinors

Optical traps and lattices: 1D, 2D systems

Optical lattices with different symmetries

Spin dependent lattices

Rotation

Disorder

Use the tools and precision of atomic physicsto realize new phenomena (Hamiltonians)

of many-body physicsCondensed-matter physics at ultra-low densities(100,000 times thinner than air)

slide69

BEC I

Ultracold fermions

Martin Zwierlein

Christian Schunck

Andre Schirotzek

Peter Zarth

Ye-ryoung Lee

Yong-Il Shin

BEC II

Na2 moleculesNa-Li mixtureOptical Lattices

Kaiwen Xu

Jit Kee Chin

Daniel Miller

Yingmei LiuWidagdo Setiawan

Christian Sanner

BEC III

Atom chips, surface atomoptics

Tom Pasquini

Gyu-Boong Jo

Michele Saba

Caleb Christensen

Sebastian WillD.E. Pritchard

BEC IV

Atom opticsand optical lattices

Micah Boyd

Erik Streed

Gretchen Campbell

Jongchul Mun

Patrick Medley

D.E. Pritchard

$$

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NASA

DARPA

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