Engineering and Control of Cold Molecules N. P. Bigelow University of Rochester

Engineering and Control of Cold Molecules

N. P. BigelowUniversity of Rochester

Why Cold (Polar) Molecules ?


Talks from:Shlyapnikov

PfauBurnett

Sengstock...


Talks from:Shlyapnikov

PfauBurnett

Sengstock...

More Reasons Later in Talk

So what about cold molecules?

Hard to find cycling transitions

Laser cooling of molecules is hard if not impossible

Doyle approach - Thermalizationwith cold helium gas &

magnetic trapping

Dilution Refrigerator

~mKParamagnetic molecules

Large samples

Meijer - time and spatially varying E fields – decelerator –

(à la high-energy in reverse; H. Gould)

accelerate

Meijer - decelerator (à la high-energy; H. Gould)

decelerate

Here

“Build” the molecules

from a gas of

pre-cooled atoms

via photoassociation

A Quick Review ofPhotoassociation

Starting with Homonuclears

Molecular potentials

Ground state

Singly excited state

Homonuclear

Photoassociation

Ground state


photon

600-1000Å

Ground state molecule formation?

Ground state

Excited state

photon

Sp. emission

(transition rate) (collision rate& pair distribution)*

(excitation rate)*(survival rate)*(process probability)*

(density2)*(volume)

These factors determine molecular production rates

Ground state molecule formation

photon

Sp. emission

i

f

Poor Franck-Condon factors are discouraging f i 0

In 1997 Pierre Pillet and co-workers startled the community

by showing the Cs2 ground-state molecules were produced

in a conventional optical trap

R-transfer methodFrank-Condon Matching

Why not heteronuclear molecules?

Molecular potentials

Ground state


Far better Franck-Condon factors….

We might be CLOBBERED by the pair distribution function

Rhomo/Rhetero = 950/76 ~ 13

(Rhomo/Rhetero = 950/76 ~ 1/10)2 ~ 100 !

The interaction time is also smaller by a factor of ~ 13!

Nevertheless, several groups

built multi-species MOTs -

including Rochester and Sao Carlos and

Kasevich

Arimondo

Ingusio

Weidemuller

Windholz

DeMille

Stwalley/Gould

Wang/Buell

Ruff

others

Bose-Fermi&Isotopic: Jin, Salamon, Ertmer, Ketterle, Hulet, Sengstock…

Sukenik

NaCsNaKNaRbRbCsKRbLiCsLiNa

?

Most “reactive”

We started with Na + Cs

Search for ground state molecules - the detection pathway

20-200 J 9ns 580-589 nm 2 mm2

NaCs formation and detection

Traps

100J pulse @ 575-600nm

time (s)

-30 0 20 105

9ns

Choice of pulsed laser wavelength

575-600 nm was chosen

To implement a resonant ionization pathway

It has enough energy to 2-photon ionize

NaCs

It will NOT resonantly ionize Cs

0

500

1000

1500

2000

2500

0 5 10 15 20

Time (s)

Co

un

t Na+Cs

Cs

Na

Na+Cs Lin Scale Zoomphotons

cold Na

Thermal Na

Cold Cs

Cold NaCs

Cs2Na2

Time of Flight

Is NaCs formed by the ionizing pulse ?

Traps

Ionizing Pulse

time (s)

-30 -15 0 20 105

9ns

Na-push beam

Push –beam experiment

How cold are the molecules?

We use time-of-flight from the interaction zone as our probe

0

10

20

30

40

50

60

70

80

90

100

12.6 12.8 13 13.2 13.4 13.6

Time (s)

Co

un

t

21

100

500

1000

2000

3000

4000

4500

4980

NaCs Temp

TNaCs ~ 260 K0.2 m/s

(kinetic temp)

KNaCs : The rate of formation

We detect 500 molecules in 10,000 pulses

Estimate ionization and detection efficiency ~ 10%

Kinetic model : 90% of NaCs drifts out of the

trapping region between pulses.

Production rate ~ 50 Hz

d [NaCs] / dt = KNaCs [Na][Cs]

KNaCs ~ 7.4 x 10-15 cm3 s-1

Measured depth of the triplet is 137-247 cm-1

Neumann & Pauly Phys. Rev. Lett. 20, 357-359 (1968).

and J. Chem. Phys. 52, 2548-2555 (1970)

We have scanned 0 – 268 cm-1 and found strong ion signals

(includes 5% of singlet potential)

We have a mixture of singlets and triplets

C. Haimberger, J. Kleinert, npb PRA Rapid Comm.

70, 021402 (R) Aug 2004

NaCs has largest polarizability (measured) of all bi-alkalis

Coherent Transfer - State Selective

Ro-vibrational ground state (lower dipole moment)or

Single excited ro-vibrational state

Incoherent transfer results already at Yale

The most important partof this part of our work:

C. HaimbergerJ. Kleinert

(M. Bhattacharya, J. Shaffer & W. Chalupczak)

KRb

RbCs

40,000 molecules/sec !!

KRb

Franck-Condon Factors for hetero-pairs based on long range (dispersion) potentials

Wang & Stwalley, J. Chem Phys.

Cold (Polar) Moleculesand Quantum Information

0

500

1000

1500

2000

2500

0 5 10 15 20

Time (s)

Co

un

t Na+Cs

Cs

Na

Polar Molecules Allow Coupling Enabling Quantum Information Applications

• Heteronuclear molecules are highly polarizable

• The dipole-dipole coupling of the molecules can be harnessed for quantum information applications (see protocols for EDMs in Quantum Dots - e.g. Barenco, et al PRL 82 1060)

Polar Molecules Allow Couplings Enabling Quantum Information Applications(based on scheme by Côté, Yellin [Lukin])

-6

-5

-4

-3

-2

-1

0

1

0 10 20 30 40

Internuclear Separation (Å)

En

erg

y (

10

3 c

m-1)

atoms

boundmolecularstates


-6

-5

-4

-3

-2

-1

0

1

0 10 20 30 40


En

erg

y (

10

3 c

m-1)

atoms


v, j 0

v , j 1

v , j v

•Start with two molecules in same state

Ai 0

Bi 0


-6

-5

-4

-3

-2

-1

0

1

0 10 20 30 40


En

erg

y (

10

3 c

m-1)

atoms


v, j 0

v , j 1

v , j v

•Start with two molecules in same state

•Use Raman pulses - create superposition

Ai 0

Bi 0

A a0 0 a1 1

B b0 0 b1 1


-6

-5

-4

-3

-2

-1

0

1

0 10 20 30 40


En

erg

y (

10

3 c

m-1)

atoms


v, j 0

v , j 1

v , j v

AB c00 00 c11 11 c01 01 c10 10

Two-molecule state:


v, j 0

v , j 1

v , j v

(large dipole moment)

Now excite to the state


v, j 0

v , j 1

v , j v

(large dipole moment)

AB c00 00 e ic11 11 c01 01 c10 10

Now excite to the state , wait an Interaction time then de-excite back to 1

Phase gate, CNOT gates etc. possible

“Dipole blockade and quantum information processing using mesoscopicAtomic ensembles”, Lukin, Fleischhauer, Côté, Duan, Jaksch, Cirac and ZollerPRL 87 037901

A specific qubit platform

Each atom sees a local field that couples it to its neighbors and permits selective addressing

The coupling cannot be switched off but instead can be compensated using echo-type refocussing techniques of NMR.

What is needed is a source of cold molecules

D. DeMille, PRL 88, 067901

E a

E ext (xa )

E int (xa )

Molecules and “Chips”

Atom Chip

Si(1mm)

SiO2(250nm)

Ag(50nm)Cu(1mm)

+-- polarization

IB~15-20 A

IS~1-3 A

Y

Z

x

B=B0y

z0

z

y

Our 1st Generation Atom Chips

20 mm

5 mm

2 mm

1 mm10 mm

y

x

w=250 m

h=1-5 m

J~ 106 A/cm2

Cross-section:

Current density:

Trap

Image of Trap

Atom chip surface

Cold AtomicMixtures-on-a-chip

Rb-Cs

Holmes, Tscherneck, Quinto-su and Bigelow

Imaging of sample

2nd Generation Chips

P. Quinto-Su, M. Tschernek, M. Holmes and N. P. Bigelow, On-chip detection of laser-cooled atoms, Optics Express, 12, 5098 (2004).

•Collaboration with Corning, Inc.

•<100 atom sensitivity

3rd Generation Chips: Molecule Chips

WHY OPTICS and MOLECULES ON THE CHIP?

Optical Fiber

Probe/readout/control laser

WHY OPTICS and MOLECULES ON THE CHIP?

4th Generation Chips

3 cm

Higher currentCapability

Heroines and Heroesof this part of the work:

Michaela TscherneckMichael HolmesPedro Quinto-SuC. Haimberger

J. Kleinert

Vortex Lattice in a Coupled

Atom-Molecule Condensate

(non-polar molecules)

Single component atomic BEC - Triangular vortex lattice

Ω is rotation frequency

Mean-field model

• Three scattering constants ga, gm and gam

• Coherent constant • Two Gross-Pitaevskii equations

Atom-Molecule BEC (homo-nuclear)

Atom-Molecule BEC – Energies

– Two key types of interaction between atoms and molecules

• Coherent coupling

• Interspecies scattering

Atom-Molecule BEC - rotating

(nv)m = 2(nv)a

Vortex density of molecular condensate istwice that of the atomic condensate

Vortex Lattice in a Coupled Atom-Molecule Condensate

(non-polar molecules)

Sungjong Woo

Department of Physics & Astronomy

University of Rochester

Q-Han Park

Department of Physics

Korea University

Summary

We can create cold diatomic polar molecules

We can create them and manipulate them on “chips”

There are interesting new aspects ofdegenerate systems involving molecules

Summary

We can create cold diatomic polar molecules

We can create them and manipulate them on “chips”

There are interesting new aspects ofdegenerate systems involving molecules

Can you calculate your Archimedes factor?

Documents

Engineering and Control of Cold Molecules N. P. Bigelow University of Rochester