Quantum dipolar gas

Precision test

Chemical reactions

Exotic phases

Lecture III: Ultracold molecules

– a new frontier

Jun Ye

JILA, NIST & CU, Boulder, CO

H2CO

OH H2O

HCO

QED

e- e-

e- e-

ICAP Summer School, Paris, July 21, 2012

Extend capability to control quantum systems

What’s new (compared to ultracold atoms)?

New internal degrees of freedom:

vibration, rotation

Chemistry

Long-range interactions

Quantum gas of polar molecules

E Exotic

quantum

matter

log 1

0(d

ensi

ty [

cm-3

])

log10(temperature [K])

-9 -6 -3 0

3

6

9

12

Novel phases & quantum many-body Dipolar quantum gas Quantum information Ultracold Chemistry

Molecule optics & circuitry Cold controlled chemistry

Novel collisions Fundamental tests Precision measurement

Science with cold molecules Carr, DeMille, Krems, Ye, New. J. Phys. 2009.

Phase space density

Dipolar quantum systems

Atoms Polar molecules

3/1 Rn

R

R

Magnetic dipoles

Electric dipoles

d ~ Debye d ~ Bohr magneton

EI~10-3 - 10-1 nK @ n=1012-1014/cm3

EI~10 - 1000 nK @ n=1012-1014/cm3

Controllable

Quantum degeneracy

~ kBT

New quantum phases and dynamics

E

E

• Correlated Fermi pairs

• Bi-layer Bose condensation?

• Super solids?

• … …

Zoller, Demler, Santos, … …

Atom vs. molecule

T = 100 nK

N = 106 atoms

n = 1013 cm-3

Bose-Einstein Condensation

1995

Molecules (pre-2008):

T = 100 mK, n = 106 cm-3

Molecules are complex!

6000 K

0.1 K 38 μK 100 K

10 orders of magnitude

1010 108 105 102 1

200 nK

Ultracold molecules: The challenge

vibration

binding

energy

rotation hyperfine translation

1 μK

trap depth

How do you cool molecules?

Chemistry Cooling (make molecules)

Cooling Chemistry (make molecules)

Cooling stable molecules

Pairing ultracold atoms

log 1

0(d

ensi

ty [

cm-3

])

log10(temperature [K])

-9 -6 -3 0

3

6

9

12

Stark, magnetic,

optical deceleration

Buffer-gas cooling

Photo-association

Coherent state transfer

Quantum degeneracy

Enhanced PA? Laser cooling? Sympathetic cooling? Evaporative cooling?

Technology for cold molecules

Quantum degeneracy

~ kBT F-space density

Two systems in the quantum regime: KRb (0.5 Debye), Ni et al., Science 322, 231 (2008) Cs2, Danzl et al., Faraday Disc. 142, 284 (2009).

Deceleration of ground-state molecules

Slower Electrodes

Pulsed valve

Skimmer

Hexapole

140 pairs of electrodes

Magnetic trap

Magnetic trap

Dipolar collisions between OH & ND3 Phys. Chem. Chem. Phys. 13, (2011) Cover

Evaporative cooling of OH

Inelastic dipolar collisions

Evaporative cooling

Data: May 2012

Phys. Rev. Lett. 101, 203203 (2008).

Sawyer et al., Phys. Rev. Lett. 98, 253002 (2007).

Evaporative cooling!

A magneto-optic trap (MOT) for molecules

A magneto-optic trap (MOT) for YO molecules

DeMille et al., Nature (2010): demonstration of 1D laser cooling Stuhl et al., Phys. Rev. Lett. 101, 243002 (2008): First proposal

uncooled 25 mK

MOT 5 mK

Quantum gas of polar molecules

40K Fermions 87Rb Bosons

K. Ni et al., Science 322, 231 (2008).

KRb molecules (Dipole ~0.5 Debye)

Temperature ~ 120 nK

T/TF = 1.0

Density ~1012/cm3

r ~ 0.2 (1011 enhancement)

10000 times colder, 1000000 times more dense than other results for polar molecules!

Start with ultracold atoms.

40K 87Rb

K-Rb Feshbach resonance

Make large, floppy molecules

Control the interactions.

Convert a pair of atoms into a molecule

0 5 10 15 20 250

1x104

2x104

3x104

4x104

mo

lecu

le n

um

be

r

hold time (ms)

Lifetime = 3 ms

6000 K!

Weakly bound molecule lifetime

atoms 100 s

weakly bound molecules 0.003 s

104 K

10-7 K

Translation energy ~ 10-7 K, Zero entropy increase

Shrink molecules without heat?

Light provides the answer

Photons carry away the energy!

Laser light

Laser light

w1

w2

3S

1S

3S

1P

Inter-nuclear distance R

Ene

rgy

v = 0, N = 0, J = 0

Good Franck-Condon for both up and down transitions. Excited state is triplet + singlet mixture

Sr

2

w1

w2

n

Frequency comb (f – stabilized)

Coherent two-photon transfer Ni et al., Science 322, 231 (2008) Ospelkaus et al., Nature Phys. 4, 622 (2008)

60

00

K

Population transfer

• 92% efficiency

• Fully coherent

(no heating)

IRb=3/2

B=546 G

0

-0.001

-0.002

0.002

0.001

IK=4

mIK=

-4,-3,….3, 4

-3/2 -1/2 1/2 mIRb=3/2

Energ

y (

GH

z)

36 states

DmIRb=-1

Hyperfine structure for 1S (v=0, N=0) S. Ospelkaus et al., PRL 104, 030402 (2010).

T = 200 nK > 1 s lifetime

Density (

10

12

cm

-3)

2)()( tntn

Two-body loss

Time (s)

Trapped molecules in the lowest energy state (electronic, vibrational, rotational, hyperfine)

Molecular quantum statistics

Cold collisions between identical Fermions (1) Particles behave like waves

(2) Angular momentum is quantized

(3) Quantum statistics matter

0110 Fermions c L = 1, p-wave collisions

s p d

0 1ħ 2ħ

KRb+ KRb K2+Rb2 +

Ultracold chemistry

At low T, the quantum statistics of fermionic molecules suppresses chemical reaction rate!

Energ

y

distance between the molecules

deBroglie wavelength

Ospelkaus et al., Science 327, 853 (2010).

KRb+ KRb K2+Rb2 +

Distinguishable molecules do not enjoy the suppression

Energ

y

distance between the molecules

deBroglie wavelength

Ultracold chemistry

Temp. (mK)

β (p-wave) ∝ T

β (s-wave)

2/)1(~ rll

24mK

6

6 / rC

(p)= 1.2(3)x10-5cm3/(s K) T

Wigner threshold law

Bimolecular reactions under

Dipolar molecular collisions

-1.5 kV

+1.5 kV

distance

1.3 cm

E = 0 (no induced dipoles) p-wave suppression

Dipolar interaction “turns on” collisions - anisotopic, long range

K.-K. Ni et al., Nature 464, 1324 (2010).

Anisotropic dipolar collisions

Collisions in 3D space average over different channels.

mL = +1, -1

mL = 0

p-wave barrier

0.01 0.1

1

10

(B)

Dipole moment (Debye)

/ T

(1

0-5cm

3s

-1K

-1)

Control the inelastic collisions with d

Long-range potential

= const. (van der Waals

interaction)

~ d6 (Attractive dipole dipole interaction)

0 1 2 3 4 50.0

0.1

0.2

d (

De

bye

)

E (kV/cm)

v1=0, v2=0

v1=0 , v2=1

|1>

|2>

|3>

R

V

|3> |2> |1> >> >>

v=2

v=1

v=0

(3)

x

y

z

E

(2) (1)

Quantized stereo-dynamics of chemical reactions

2 molecules in the same internal & |v> states

|L = 1, mL = ±1 >

2D quantum gas - suppress losses

z

0.00 0.05 0.10 0.15 0.20

10-12

10-11

10-10

10-9

3D

D

D (

cm

3s

-1)

Dipole moment (D)

E

M. de Miranda, et al., “Controlling the quantum stereodynamics of ultracold bimolecular reactions,” Nat. Phys. 7, 502 (2011).

Polar molecules in 3D lattice

0 5 10 15 20 250

2

4

6

8

10

nu

mb

er

(10

3)

time (s)

One body loss fit

t = 25(2) s

No loss

Long-range interactions

Quantum magnetism

Chotia et al., Phys. Rev. Lett. 108, 080405 (2012).

|N=0>

|N=1>

Lifetime independent of dipole

Cold molecules:

Amodsen Chotia Silke Ospelkaus Kang-Kuen Ni Dajun Wang Marcio Miranda Brian Sawyer Eric Hudson

Theory collaborations: Goulven Quéméner, John Bohn, Svetlana Kotochigova, Paul Julienne

Bo Yan Brian Neyenhuis Steven Moses Jake Covey Matt Hummon Ben Stuhl Mark Yeo A. Colopy

Debbie Jin