talk Cold Mg Atoms for Optical Clock · 2007-09-12 · Holger Wolf Dr. Jochen Keupp Dr. Albane Douillet The Mg - Atom Interferometry group in Hannover. Outline • Brief history of

Institute of Quantum OpticsUniversity of HannoverWelfengarten 1D-30159 HannoverGermany

Cold Magnesium Atoms for an Optical ClockCold Magnesium Atoms for an Optical Clock

Tanja Mehlstäubler

Jan FriebeVolker Michels

Karsten MoldenhauerNils Rehbein

Dr. Hardo StöhrDr. Ernst-Maria Rasel

Prof. Dr. Wolfgang Ertmer

Jan Friebe

Volker Michels

Tanja Mehlstäubler

Karsten Moldenhauer

Nils Rehbein

Dr. Hardo Stöhr

Dr. Ernst-Maria Rasel

Prof. Wolfgang Ertmer

former members:

Holger WolfDr. Jochen KeuppDr. Albane Douillet

The Mg - Atom Interferometry group in Hannover

OutlineOutline

• Brief history of frequency standards

• Ramsey-Bordé interferometery in Mg

• How to get to µK temperatures ?

(A) 25Mg and heating in MOT

(B) Quench cooling

(C) 2-photon resonances

• Summary & Outlook

cy Stability

A brief history of frequency standardsA brief history of frequency standards

cy Accuracy δν/ν0

τσν

∆=Q,

• microwave standards

1950 : Ramsey develops seperated field method

Ø atomic beam clocks surpass quarz

1989 : “a Mg atomic beam frequency standard” Bava et al., Appl. Phys. B, 48, p.495, (1989)

1989 : first fountain (Na): ∆ν∆ν∆ν∆ν = 2 Hz

Kasevich et al., PRL, 63, p.612, (1989)

• optical standards

neutral alkaline-earth (like) atoms Æ high S/N

1992 : “the Mg Ramsey interferometer” Sterr et al., Appl. Phys. B, 54, p.341, (1992)

1999 : narrow line cooling in Sr : ρ : ρ : ρ : ρ ~ 10-2 in MOT Katori et al., PRL, 82, p.1116, (1999)

2001 : quench cooling in Ca: TMOT ~ 6 µK Binnewies et al., PRL, 87, 123002, (2001)

Curtis et al., Phys. Rev. A, 64, 031403, (2001)

2003 : Yb BEC via narrow line cooling ! Takasu et al., PRL, 91, 040404, (2003)

δν/ν0 = 7µ10-16

σy = 1.6µ10-14 in 1s

(Cs/Rb fountains)

δν/ν0 = 1.2µ10-14 (Ca)

σy = 7µ10-15 in 1s

(Ca/Hg+ comparison)

The magnesium atomThe magnesium atom

• 457 nm clock transition

– atomic quality factor

Q=2â1013

– potential for T < µK(1)

• 285 nm cooling transition

– strong light forces

– high TD ~ 2 mK

(1) H. Wallis and W. Ertmer, J.Opt.Soc.Am. B 6, 2211 (1989)

285 nm

80 MHz

Singlet Triplet

1S01P1

1D23S1

3P0123D123

457 nm, 31Hz - Interferometry

462 nm

4 MHz 881 nm

laser beam/puls

Pex ∂ cos(2TD(∆+δrec))

Ch. Bordé, C.R. Acad. Sci. Ser. B, 284, p.101 (1977)

• Doppler free Ramsey spectroscopy

ULE-ULE-ULE-ULE-

resonatorresonatorresonatorresonator

Eddie currentEddie currentEddie currentEddie current

dampingdampingdampingdamping

intermediateintermediateintermediateintermediate

massmassmassmass

springspringspringspring

mountismountismountismountis

12,5 cm12,5 cm12,5 cm12,5 cm

16 cm16 cm16 cm16 cm

Ramsey-Bordé InterferometryRamsey-Bordé Interferometry

457 nm

285 nm

• 140 mW at 457 nm with dye laser

• stabilized to high finess cavities

Ramsey-Bordé InterferometryRamsey-Bordé Interferometry

• resolution 280 Hz

• potential stability σy = 8 x10 -14

• laser line width ∆υLaser § (170 ≤ 15) Hz

ï atomic motion limits stability

ï only 8 % of atoms are excited (τPulse= 4 µs)

decay of signal

TMOT = 3.8 mK

39600 40000 40400 40800 412001100000

1120000

1140000

1160000

1180000

1200000

1220000

1240000

σy(τ= 1s) = 7.64 10

detuning [Hz]

T = 860,8 µs

21.05.02

290 Hz resolution

N = (8700±1000)s-1

S = 16000

Q = 2.26 1012

0,0 0,2 0,4 0,6 0,8 1,0 1,2

Stotal

Doppler limit

0 2 4 6 8 10 12 14 16 18 20

[108/cm

change of oven temperature misaligned MOT

change of laser intensity

Temperatures in MOTTemperatures in MOT

• new set up to study cooling techniques

• optical access for UV, quenching, interferometry, dipole trapping

• up to108 atoms

MOT coils (grad B = 130 Gauss/cm)Mg beam slowing beam

Sub-Doppler forces in Sub-Doppler forces in 2525MgMg

[ΓΓΓΓ/k]]]] [ΓΓΓΓ/k]]]]

γ]γ] γ]γ]

∆=19 MHz

∆=27 MHz

γ=80 MHz

Ω/Γ=1

γ]γ] γ]γ][h

kγ]γ] γ]γ]

B=16 MHz

B=0 MHz

Sub-Doppler cooling of 25Mg ?

(Coop. J.Dunn, J.Ye, NIST)

γ]γ] γ]γ][h

kγ]γ] γ]γ]

γ]γ] γ]γ][h

kγ]γ] γ]γ]

Ω/Γ=0.25

Hyperfine Quenching of

clock transition 1S0→3P0 :

90 µHz → 0.44 mHz(Porsev u. Derevianko, physics/0312006,

Dez.2003)

> 105 atoms

in MOT

Isat =450 mW/cm2

Sub-Doppler forces in Sub-Doppler forces in 2525MgMg

γ]γ] γ]γ]

Ω/Γ=1Sub-Doppler cooling of 25Mg ?

(Coop. J.Dunn, J.Ye, NIST)

Hyperfine Quenching of

clock transition 1S0→3P0 :

90 µHz → 0.44 mHz(Porsev u. Derevianko, physics/0312006,

Dez.2003)

> 105 atoms

in MOT

87Sr 25Mg

(s = 2) vc ~ 0.07 m/s vc ~ 0.22 m/s

(s=0.13) vc ~ 0.02 m/s

vrec= 0.01 m/s vrec= 0.06 m/s

in MOT:

vrms= 0.4 m/s vrms= 1.1 m/s

∆=19 MHz

∆=27 MHz

γ=80 MHz

Isat =450 mW/cm2

Quench cooling in Quench cooling in 2424MgMg

• cooling on narrow lines

• 31S0 → 33P1 : Trec = 3.8 µK >> TDopp

• mg<Flight → γmin~90 Hz

• quench transition 33P1 → 41S0

200 mW @ 462 nm with Ti:Sapph

doubled with PPKTP

Clock transition457 nm 31Hz

MOT285 nm80 MHz

quench laser462 nm

γ = 4 MHz

Ω12, Γ1

Ω23, Γ2

γeff 31Hz

T.E. Mehlstäubler et al., J.O.B 5, p.183 (2003)

ILaser

Ω+Γ=Γeff

232233

Ω×= ρρ

33312222 Γ+Γ=Γ ρρρ eff

for s3 <<1:

462 nm

457 nm

llll/2

Mg ovenT ~ 410 °C

detection

Mg beam

interaction zones

retro reflector

excitation

41S0llll/2

Search for the quenching transitionSearch for the quenching transition

Kuruzc: ΓΓ2 2 = = 3.21 10³ s3.21 10³ s-1-1

new ab initio calculations:

Pal’chikov, Derevianko, Fischer(3)

ΓΓ2 2 = = 2.0 x 102.0 x 1022 s s-1-1

our measurement:

ΓΓ2 2 ~ ~ 1 x 101 x 1022 s s-1-1

Quench cooling in Quench cooling in 2424MgMg

(3) private communications, to be published

→ theo. transfer efficiency ~ 1%

→ x • 104 atoms expected @ T=10µK

→ 8% of 105 atoms, 70% of x • 104 atoms

→ lower duty cycle of interferometry

0 5 10 15 20 25 30

PQuench

[mW] per beam

(larger power @ 457nm)

0 200 400 600 800 1000

PQuench

[mW] per beam

(larger power @ 457nm)

2-Photon resonances in 2-Photon resonances in 2424MgMg

W.C. Magno et al., Phys. Rev. A 67, 043407 (2003)

• 2-photon process more efficient

than 1 photon ?

2.2 MHz881 nm

80 MHzUV-MOT

loss3P1,2

ρ3 (IR)

ρ2 (UV)

exact solution of the Bloch equationsexact solution of the Bloch equations

for a 3 level systemfor a 3 level system

80 MHz

-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50

= 1.3 mW

σ = 16 MHz

= 44 mW

σ = 26 MHz

detuning of 881 nm laser [MHz]

Resonance in MOT

W.C. Magno et al., Phys. Rev. A 67, 043407 (2003)

• 2-photon process more efficient

than 1 photon ?

2.2 MHz881 nm

80 MHzUV-MOT

loss3P1,2

resonances in 1D molasses resonances in 1D molasses

60 80 100 120 1402

ν (IR) in MHz

scan7b

26 mK 21 mK

30 45 60 75 90 105 1200

ν (IR) in MHz

Temperature across 2-photon resonance

Populations in excited states

fi force at UV transition:

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-4 -2 2 4

-40000

-20000

-3 -2 -1 1 2 3

-40000

-20000

-3 -2 -1 1 2 3

-40000

-20000

-2 -1 1 2

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-4 -2 2 4

-40000

-20000

-4 -2 2 4

-40000

-20000

-2 -1 1 2

-40000

-20000

-2 -1 1 2

-40000

-20000

-3 -2 -1 1 2 3

-40000

-20000

-2 2 4

-40000

-20000

-4 -2 2 4

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

-6 -4 -2 2 4 6

-40000

-20000

• positive feedback on faster atoms (bunching)

• higher friction for low velocities

v[m/s]

-4 -2 2 4

-20000

-10000

-0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-3 -2 -1 1 2

-10000

-0.002 -0.001 0.001 0.002 0.003

-2 -1 1 2

-0.002 -0.001 0.001 0.002 0.003

-2 -1 1

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-3 -2 -1 1 2 3

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-2 -1 1 2

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-2 -1 1 2

-0.002 -0.001 0.001 0.002 0.003

-2 -1 1 2

-0.002 -0.001 0.001 0.002 0.003

-3 -2 -1 1 2 3

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003 0.004

-4 -2 2 4

-20000

-10000

-0.002 -0.001 0.001 0.002 0.003

-4 -2 2 4

-20000

-10000

-0.001 0.001 0.002 0.003

-4 -2 2 4

-10000

-0.001 0.001 0.002 0.003

• force at UV transitionfi dv = a(v) dt

• integrating eqs. of motion• TOF after 100µs molasses

-4 -2 2 4

-20000

-10000

-0.004 -0.002 0.002

T < 100 µK ?

e.g. for balanced molasses

Summary & OutlookSummary & Outlook

• Mg interferometry limited by temperature of atoms

• Sub-Doppler cooling forces in 25Mg are not sufficient

• Quenching transition @ 462 nm measured

Ø load 1% of atoms into QMOT at 9 µK ?

• 2-photon resonances observed

Ø Sub-Doppler temperatures possible

in 3D-molasses ?

Ø Channel to populate meta-stable states !

• Combination with dipole trap ?

Udip [MHz]

400 600 800 1000

λtrap [nm]

ac-Stark-shift

1S0 m = 0 π

3P1 m = 0 σ +/−

m = +1 / -1 σ −/+

m = -1 / +1 σ +/−

w0 = 20 µm

Τtrap

≈ 0.3 mK

ΓRaleigh

≈ 0.1 Hz

- Yb:YAG 25 W @ 1030 nm

- quench cooling into dipole trap

- study of collisions

- trap potentials only identical

at crossing Æ λλλλ = 446 nm

Summary & OutlookSummary & Outlook

Laser active medium : thin disk (~320 µm)

multiple pump light passes through the laser active medium

single frequency with 2 etalons : d = 0,6 mm und 4 mm

crystal

heatsink pump

parabolicpump mirror

etalons

700 mW@ 914 nm

Nd:YVO4

40 W @ 808 nm

outputcoupler

The thin disc laserThe thin disc laser

w1~49 µµµµm

w2~147µµµµm

cavity length = 34 cm

incoupling efficiency: 85 %

conversion efficieny: 47 %

4/λλλλ

400 mW @ 914 nm

160 mW @ 457 nm

PPKTP crystal

Cavity:Hänsch-Couillaud lock

Frequency doublingFrequency doubling

talk Cold Mg Atoms for Optical Clock · 2007-09-12 · Holger Wolf Dr. Jochen Keupp Dr. Albane Douillet The Mg - Atom Interferometry group in Hannover. Outline • Brief history of

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