D. DeMille, E.Hudson, N.Gilfoy, J.Sage, S.Sainis, S.Cahn, T.Bergeman,* E.Tiesinga†

Yale University, *SUNY Stony Brook, †NIST

• Motivation: why ultracold polar molecules?• Photoassociation: Rb + Cs RbCs* • Production & state-selective detection of metastable RbCs (v1)• Production of absolute ground-state RbCs X(v=0)• Optical trapping of metastable RbCs (v1)• The (near) future

• Enhanced sensitivity to variation of me/mp in Cs2

Production of ultracold polar molecules from atoms

FundingNSF, Keck Foundation, DOE

Packard Foundation

DeMille

Group

Jeremy Sage

Sunil Sainis

Jamie Kerman

Tom Bergeman

(Stony Brook)

EiteTiesinga(NIST)

Nate Gilfoy Eric Hudson

Theory

Experiment (Yale)

Applications of ultracold polar molecules

• Electrically polarized molecules have tunable interactions that are extremely strong, long-range, and anisotropic--a new regime

New, exotic quantum phases checkerboard, supersolid, BCS, etc.

Models of strongly correlated systems quantum Hall, lattice spin systems,

dipolar Wigner crystals, layered/chained systems, etc.Large-scale quantum computation

• Coherent/quantum molecular dynamicsNovel collisional phenomena Ultracold chemical reactions

• Precision measurements/symmetry tests--narrow lines improve sensitivity AND--molecular structure amplifies effectsTime-reversal violating electric dipole moments (103 vs. atoms)Parity-violation: anapole moments/Z0 boson couplings (1011!)Time-variation of fundamental constants (also non-polar)

Bohn, Krems, Dalgarno, Hutson,Balakrishnan, Meijer, Ye et al., etc…

Hinds et al., Doyle, D.D., Ye, Flambaum, Kozlov, etc…

Zoller, Büchler, et al., Lewenstein, Lukin, Demler, Baranov, D.D., etc., etc., etc.…

-V

+V

Optical lattice w/transverse confinement

Strong E-field

Weak E-field

Electricdipole-dipole

interaction

Quantum computation w/polar molecules in a lattice

• bits = electric dipole moments of polarized diatomic molecules

• register = array of bits in optical lattice (weak trap low temp 10 K)• processor = microwave resonance w/spectroscopic addressing (robust, like NMR)

• interaction = electric dipole-dipole (strong fast CNOT gates ~ 1-100 kHz)

• decoherence = scattering from trap laser (weak trap long T ~ 5 s)• readout = laser ionization or cycling fluorescence + imaging (fairly standard)

• scaling up? (104- 107 bits reasonable?...one/site via Mott insulator w/ n 1013 cm-3)

D.D., PRL 88, 067901 (2002); Ostrovskaya; Kirby/Cote/Yellin; Kotochigova/Tiesinga;…

Cold molecules from cold atoms I: photoassociation

|e(R)|2

|g(R)|2

Ve(R)

Vg(R)“Condon radius”

RC

PAlaser

Internuclear distance R

en

erg

y

EK

S+P

S+S

• transition rates governed by free-bound* Franck-Condons

•polar molecule heteronuclear

• heteronuclear excited-state potentials have short range (r -6 only) PA harder due to van der Waals “speedup”

• electronically excited molecular states primarily decay into hot free atom pairs loss of atoms from MOTSeminal early work:Homonuclear expt.

Heinzen, Pillet, UConn, etc. (’90s)Theory: Julienne, etc.Heteronuclear expt.

Bigelow (‘98) Theory: Wang & Stwalley (’98)

spont.emiss.

MOT trap loss photoassociation spectraRbCs and Cs2 rotational

structure(Ω = 0)

RbCs rotational + hyperfine structure (Ω = 1,2)

•dozens of bandheads observed; analysis yields novel information on long-range heteronuclear potentials, non-adiabatic couplings, etc.

•hfs analysis still neededA.J. Kerman et al.,

Phys Rev. Lett. 92, 033004 (2004)

•spectroscopically selective production of individual low-J rotational states

•up to 70% trap depletion for RbCs (100%) atom-molecule conversion Similar data for

KRb (UConn ‘04), NaRb (Rochester ’07)

RbCs

Cold molecules from cold atoms II: radiative stabilization

|e(R)|2

|g(R)|2

Ve(R)

Vg(R)“Condon radius”

RC

laser

Internuclear distance R

en

erg

y

EK

S+P

S+S

•decay to hot free atom pairs or ground-state molecules (ratio from FCFs: more favorable for heteronuclear!)

•Dissipation via spontaneous emission accumulation (metastable, 1 s) BUT electronic ground state population distributed over several high vibrational states

• molecules at translational temperature of atoms (modulo two photon recoils)

•rotational state selection in PA + selection rules few rotational states (1-3)

Detection of metastable RbCs: ionization + mass spec

channeltron -2 kVelectrode

+2 kV

Cs,Rb

time 10 ns

532 nm5 mJ

670-745 nm0.5 mJ

PA laser

strong, non-

selective excitation

ionization pulseSimilar detection +

temperature measurement in many species:

RbCs: Yale, Aero. Corp.KRb: Sao Paolo, UConn

NaRb: RochesterLiCs: Freiburg

Ground-state (vibrationally excited) RbCs @T = 100 K

Time toballistically exit detection region

t ~ 10 mstranslational temperatureT ~ 100 K

delay

PA

Cold molecules from cold atoms III: stopping the vibration

|i(R)|2

EK

|g(R)|2

|e(R)|2

laser

Internuclear distance R

en

erg

y

Vg(R)

S+S

Ve(R)

S+P

•~1 rotational state•Atomic translational temperature•BUT distributed over several high vibrational states

• Laser transfer from high vibrational level to v=0:TRULY ultracold molecules (translation, rotation, vibration)

•High vibrational states•UNSTABLE •NOT POLAR

want vibrational ground state!

•NEEDED: •initial state location & population •pathway w/Franck-Condon overlap for “pump” AND “dump”

Mapping the vibrational distribution of cold RbCs

•clear ID of (2) 3+ band origin

37

36

39

38

4044

a 3+

A.J. Kerman et al., PRL 92, 153001

(2004)

•clear ID of a 3+ vibrational pattern (weakly bound)•~7% decay into most-populated a3+(v = 37) level

•big, regular patterns in spectrum yield (2) 3+ vibrational splittings

(2) 3+

weak, selective excitation

ionization

+UConn(KRb, 2005)

+ spin-orbit doubling

2nd order spin-orbit

v = 0

Epump= 9786.1 cm-1

Edump =

13622.0cm-1

•Transfer verified on ~6 separate transitions

•Estimated efficiency ~6%, limited by poor pulsed laser spectral profiles

•Narrow rotational distribution, limited by pulsed laser linewidth

(2) 3+

(1)11

J.Sage et al., PRL 94, 203001 (2005)

Production of vibronic ground state by stimulated pumping

KRb metastable (least bound state)production reported: Hamburg, JILA

Heteronuclear molecules from degenerate gases

Feshbach resonance

No dissipation needed100% transfer to single molecular state

Viable pathways for stimulation to X1+(v=0) ground state tentatively identified for ALL bialkali species (Stwalley)

Stimulated Raman?(Lattice assisted?)JILA, MIT, Florence, Hamburg,…

STIRAP: Drummond, Heinzen,...Lattice: Damski et al.;

Moore & Sadeghpour; etc.

protection fromcollisions in lattice

Ongoing work: optically trapped polar, absolute ground-state RbCs molecules

LatticeCO2

Trap

Photoassociationin optical trap

allowsaccumulation

of vibrationallyexcited molecules

Trapped molecular samplewill allow study of:

•atom-molecule collisions•molecule-molecule collisions

•dipolar effects?•chemical reactions?

1+1 REMPI& TOF mass spec

as before for state-selective

detection

Trapped RbCs lifetime vs. precursor atom density

= 270 ms ± 81 msatoms ~ 1010 cm-3

= 86 ms ± 7 msatoms ~ 1011 cm-3

Compare to: atoms ~ 4 s

Clear evidence for RbCs collisions!

Coming soon: “distilled” sample of polar, absolute ground-state RbCs molecules

LatticeCO2

TrapPhotoassociation

in optical trapallows

accumulationof vibrationally

excited molecules

STIRAPtransfer

to X(v=0)w/transform-limited lasers

DipoleCO2

Trap

+V -V

Gravity

v = 0, J = 0polar molecules

levitatedby electrostatic

potential

other species(atoms,

excited molecules)fall from trap

Anticipated:pure, trapped

sampleof >3104 RbCs(v=0)

@n>1011/cm3

T 15 K

Why study time variation of electron-to-proton mass ratio ?

( me/mp)

•Variation of “constants” motivated by--naïve models of dark energy (an experimental fact!)--ideas about extra dimensions (from string theory)--connections to equivalence principle--tentative observations in cosmological data

•Grand unified theories suggest (/) ~ 30(/) [variation of fine structure constant strongly constrained]

•Optical atomic clocks insensitive to

•Laboratory tests now comparable in sensitivity to cosmological limits

Enhanced sensitivity to d/dt with molecules( me/mp)

Vib. energy E=

/ ~k M Ry

th vib. level

enhancementin dE/d

NN

Large shiftfrom high level+huge shiftfrom nearby "anchor" level

: microwave freq.

absoluteN

Ideal

relative

Next electronicpotential well energy independent of , M

~eV

0

0.5

0 1Energy [De]

dE

/d{l

n(

)} [

De]

Sensitivity to d/dt vs. binding energy ( me/mp)

E

R

1.1

“pile-up” near dissociation limit

harmonic: linear slope=1/2

anharmonicity slows response

response 0 at De

Sensitivity vs. energy

Morsepotential

d/dt with ultracold Cs2

Internuclear distance R

En

erg

y

•ultracold Cs2 narrow lines (1 Hz?)

X 1g

+

a 3u

+

•high level densities singlet-triplet overlaps common (?)

•efficient Cs2 formation

(via photoassociation or Feshbach + stim. Raman) into deeply-bound a 3u levels

possible [favorable FC factors]

+

Two-color PA spectroscopy of Cs2

“Typical” abs. sensitivity ~ 0.01 Hz for = 10-15

100-1000 improvement over current limits feasible?

0g 6s1/2+6p3/2-

a3u 6s1/2+6s1/2+

Cs2 iondetection

+

0

200

400

600

800

1000

1200

0 1000 2000 3000 4000

Energy (cm-1)

dE/d

{ln(

)}

(cm

-1)

Cs2 X1g sensitivity to +

triplet well bottom

range studied

X1g +

Cs2

formation

PA

Probe

perturbing singlet level

perturbed triplet level

GHz binding

=4, F=10

=4, F=8,9

S=1, I=7, f=7

GHz binding

Theory:E. Tiesenga, T. Bergeman

ℓ

I

S

f F

Observation of singlet-triplet degeneracy in Cs2

• Demonstrated optical production of ultracold polar v=0 molecules: T ~ 100 K now, but obvious route to lower temperatures

• Same technique for transfer to ground state applicable to all heteronuclear bialkalis + levels produced by e.g. Feshbach association

• Formation efficiency of >5% into most-populated v 1 levels of the ground electronic state AND efficient transfer to v=0 ground state (>5% observed, ~100% projected)

•Demonstrated optical trapping of v 1 levels w/long lifetime Collisional studies of ultracold, heteronuclear bialkalis Large samples of stable, trapped, ultracold polar molecules in reach?

• New system for enhanced sensitivity to variation of me/mp identified & under investigation in Cs2

Status & Outlook: ultracold bialkali molecules from atoms

Heteronuclear polar?

from: M.Aymar & O.Dulieu,J. Chem. Phys. 122, 204302 (2005); also: Kotochigova, Julienne, Tiesinga

d<10-2D @~300 GHz

binding energy

Dip

ole

mom

ent

d (

Debye)

Weakly bound levels

little electron wavefn. hybridization

small dipole moment:

d R7 (B.E.)7/6

@long range

X 1+

a 3+

RbCsX(v=0)

d = 1.3D

Deep X1+ levelshave substantialdipole moment

d ~ 0.5-5 D(2.54 D = 1 ea0)

Dipole moments of heteronuclear bialkalis