Kenneth Brown, Georgia Institute of Technology

Probing molecular ions withlaser-cooled atomic ions

Cold Molecular Ions

15 mm

Ca+ X+?

Ion Trap

• Ions are trapped in an oscillating quadrupole field

• Ion stability is based on charge to mass ratio

• Radial pseudopotential is weaker for larger masses

RF

RFground

ground

DC DCRF

RFground

ground

DC DC

Stability condition/ [Z M kVrf/ (r0

2Wrf2)] <1

Ions for Doppler Cooling

397 nm 866 nm

S1/2

D3/2

P1/2

Ca+

40Ca+

X2 ,S v’=0

X2 , P v=0

BH+

Challenges of Laser-Cooling Molecular IonsJ. H. V. Nguyen, C. R. Viteri, E. G. Hohenstein, C. D. Sherrill, K. R. Brown, and B. OdomNew J. Phys. 13, 063023 (2011)

X2 ,S v’=1

370 nm 935 nm

S1/2

D3/2

P1/2

Yb+

172Yb+

[3/2]1/2

Doppler Laser Cooling

5

0ppatom

laseratom kpp

0 emissionlaseratom kkpp

0

After n absorption-emission cycles, the average atom momentum is reduced by nħk.

Absorbed photons must be resonant with the Doppler-shifted transition.

Cooling rate and temperature limit are proportional to the linewidth.

Doppler Recooling

R.J. Epstein et al., Phys. Rev. A 76 033411 (2007)

397 nm866 nm

S1/2

D3/2

P1/2

Simple experimental setup.Difficult for low heating rates.transition linewidth > trap frequency.

Sideband Cooling

g

e

729 nm

854 nm

nn -1

n -1

S1/2

m = -1/2

n -1

n

P3/2

m = -3/2

D5/2

m = -5/2

Sideband Measurement

397 nm866 nm

S1/2

D3/2

P1/2 D5/2

P3/2 854 nm

729 nm

J. Labaziewicz et al.Phys. Rev. Lett. 100, 013001 (2008)

Temperature measurement conceptually simpler.RSB=k<n> BSB=k<n+1>

Transition linewidth < trap frequency .

Atomic & Molecular Ions

(115 mK)

A. Ostendorff , et al., Phys. Rev. Lett., 97, 243005 (2006)

K. Mølhave and M. Drewsen, Phys. Rev. A. 62, 011401 (2000)

Laser cooled Mg+ cools MgH+

Laser cooled Ba+ cools AlexaFlour+

Laser-cooled MS: T. Baba and I. Waki, Jpn. J. Appl. Phys., 35, L1134025 (1996)

Molecular Ion Spectroscopy

J. C. J. Koelemeij, et al.Phys. Rev. Lett. 98 173002 (2007)

Fluorescence detected REMPD

Molecular Ion Spectroscopy

Action Spectroscopy

X. Tong, A. Winney, and S. WillitschPhys. Rev. Lett. 105 143001 (2010)

N2+ + Ar Ar+ + N2

This reaction is energetically forbidden when N2

+ is in the ground state.

One Ion Limit

Ca+ CO2+

1. Trap atomic and molecular ions2. Laser cool ion crystal

3. Heat ion crystal by exciting the molecular ion.

4. Measure temperature change by laser-induced atomic fluorescence

Quantum Logic Spectroscopy

A

B

g

e

0

1

A

B

g

e

0

1

A

B

g

e

0

1

Control Spect. Motion

Sideband cool to vibrational ground state of the crystal.

Excite the spectroscopy ion at the A-B transition plus one motional quanta.

If the motion is excited, the g-e transition minus one motional quanta can be observed.

Initialize

Probe

Detect

P. O. Schmidt et al., Science 309, 749 (2005)

Be+-Al+ Clock

Figures from P. O. Schmidt et al., Science 309, 749 (2005)Clock measurement described in T. Rosenband et al., Science 319, 1808 (2008)Tests of Relativity C. W. Chou et al., Scienc, 329, 1630 (2010)

A

B

g

e

Control Spectroscopy

A-B transition in Al+ measured by monitoring the population in g by Be+ fluorescence.

QLS and SHS

Quantum Logic Spectroscopy Detect single phonon excitation Coherent excitation of spectroscopy ion P. O. Schmidt et al., Science 309, 749 (2005)

Sympathetic Heating Spectroscopy Detect heating rate by recooling (or by

phonons) Incoherent excitation of the spectroscopy

ion C.R. Clark, J.E. Goeders, Y. Dodia, C.R. Viteri, and KRB, PRA,

81, 043428 (2010)

C.R. Clark, J.E. Goeders, Y. Dodia, C.R. Viteri, and KRB, PRA, 81, 043428 (2010)

Sympathetic Heating Spectroscopy

397 nm866 nm

S1/2

D3/2

P1/2 40

44

Isotope Abundance 40Ca 96.9% 44Ca 2.09%

D. Lucas et al., PRA 69, 012711 (2004)

Isotope Shift 44Ca 1S0-1P1 : 774 MHz

44Ca+ S1/2-P1/2: 842 MHz

44Ca+ D3/2-P1/2: -4495 MHz

Cooling vs Heating

Cooling

Heating

LIF

0 50 100 1500

20

40

60

80

100

Ph

ea

t

0 50 100 1500

50

100

150

200

I LIF

44397

(MHz)

44s866

=944s

866=2

44s866

=0.544s

866=0.1

SHS (theat=250 ms)

# o

f Photo

ns

40s397=7 40s866=1000 tmeas=3 ms

44s397=0.03 tmeas=750 ms

40Ca+

44Ca+

cool

heat

recool

SHS Limits

-20 0 20 40 60 80 1000

10

20

30

40

50

60

44397

(MHz)

Phe

at

44s

397=110-2

44s866

=110-3

44s397

=044s

866=0

For theat = 1s, there is measurable trap heating.

theat = 1strecool = 0.39 stint = 0.5 s

Compare to tmeas=1.89 s.Calculated fluorescence lost in the detector noise.

<1000 photons into 4p

J. E. Goeders, C. R. Clark, G. Vittorini, K.E. Wright, C. Ricardo Viteri, and KRB

Resolved Sideband Mass Spectrometry

729 nm laser

Central frequency drifts less than 10 kHz over 7 hrs

ATFilms ULE Spacer100,000 finesse500 MHz FSR

Zeeman Spectroscopy

729 nm

397 nm866 nm

Zeeman Spectroscopy

Normal Modes of Two Ions

Axial modes

Axial frequency of M1 M1/M2 M. Drewsen et al.

PRL 93 243201 (2004).

Two Calcium Ions

COM

BM

S1/2-D5/2

Frequency Offset [MHz]

Inte

nsi

ty (

Arb

. U

nit

s)

Other Ions

Load CaH+ or CaO+ by leaking in 10-9 - 10-8 torr H2 or O2

Load other isotopes by resonant enhanced two photon ionization

Center of Mass Mode

40Ca+ -40Ca+

40Ca+ - 40CaO+40Ca+ -

48Ca+

40Ca+ - 44Ca+

40Ca+ - 43Ca+

40Ca+ - 42Ca+

40Ca+ - 40CaH+

Frequency Offset (MHz)

P

op

ula

tion in

D5

/2

-0.74 -0.72 -0.70 -0.68 -0.68 -0.64

0.2

0.3

0.1

J. H. V. Nguyen, C. R. Viteri, E. G. Hohenstein, C. D. Sherrill, K. R. Brown, and B. OdomNew J. Phys. 13, 063023 (2011)

Application to laser-cooling BH+

Click icon to add picture

Laser Cooling of SrFDeMille and coworkersPhys. Rev. Lett. 103, 223001 (2009)Nature 467, 820 (2010)

K=0 K=1 K=2 K=3

S

P

2

2

v’=0

v’=1

v’=n

v=0

v=1

K=0 K=1 K=2

v’=0

v’=1

v’=n

v=0

S2X

S2B

P2A S2Xdissociative

ComplicationsParity ViolationVibrational DecayPhotodissociationPredissociation

BH+

Vibrational relaxation transforms spread in vibrational states into a spread in rotational states

379nm

417 nm

Precision Spectroscopy

v’=0

v’=1

S2X

P2A v=0

Cooling lasers:v=0←v’=0, ΔJ=0,-1C1-C2 (one laser plus EOM)C3-C4 (two lasers)

Repump lasers:v=0←v’=1 ΔJ=0,-1R1-R2 (one laser plus EOM)R1-R4 (one pulsed laser)v=0←v’=0, ΔJ=-1PR1-PR2 (one pulsed laser)

Photons Scattered

Conclusions and Outlook

Single ion techniques can be used to accurately measure lines for both allowed and forbidden transitions

BH+ is a promising candidate for direct laser cooling

Vibrational overtones of CaH+ are good QLS candidates (wavelengths from M. Kajita) 9-0 889.4 nm 10-0 819.5 nm 11-0 764.18 nm

http://j.mp/brownlab

Cold Molecular Ions

Surface Electrode Traps

QEC and ResourcesQ1 T|+ A

Postdoc position available