talk cold mg atoms for optical clock · 2007-09-12 · holger wolf dr. jochen keupp dr. albane...
TRANSCRIPT
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
time
ν0
freq
uen
cy Stability
A brief history of frequency standardsA brief history of frequency standards
time
ν0
freq
uen
cy Accuracy δν/ν0
2/1
2 1)(
=
TN
SQ
y
τπ
τσν
ν
∆=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)
MOT
285 nm
80 MHz
Singlet Triplet
1S01P1
1D23S1
3P0123D123
457 nm, 31Hz - Interferometry
0
21
J=0
462 nm
4 MHz 881 nm
24Mg
laser beam/puls
π/2
TD TD
Pex ∂ cos(2TD(∆+δrec))
|gÚ
|eÚ
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
3P1
1P1
1S0
457 nm
31 Hz
285 nm
MOT
• 140 mW at 457 nm with dye laser
• stabilized to high finess cavities
24Mg
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
-14
coun
t ra
te [
s-1]
detuning [Hz]
T = 860,8 µs
21.05.02
290 Hz resolution
N = (8700±1000)s-1
S = 16000
Q = 2.26 1012
r60b
0,0 0,2 0,4 0,6 0,8 1,0 1,2
2
4
6
8
10
12
14
16
Tem
per
atu
re [
mK
]
Stotal
24
Mg
25
Mg
Doppler limit
0 2 4 6 8 10 12 14 16 18 20
2
3
4
5
6
7
8
N1/3
n2/3
[108/cm
2]
change of oven temperature misaligned MOT
change of laser intensity
Mg25
Te
mp
era
ture
[m
K]
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]]]]
[hk
γ]γ] γ]γ]
F=5/2
F=3/2
F=5/2
F=7/2
∆=19 MHz
∆=27 MHz
γ=80 MHz
25Mg
87Sr
Ω/Γ=1
[ΓΓΓΓ/k]]]] [ΓΓΓΓ/k]]]]
[hk
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)
[hk
γ]γ] γ]γ][h
kγ]γ] γ]γ]
[hk
γ]γ] γ]γ][h
kγ]γ] γ]γ]
[ΓΓΓΓ/k]]]] [ΓΓΓΓ/k]]]]
25Mg
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
[ΓΓΓΓ/k]]]] [ΓΓΓΓ/k]]]]
[hk
γ]γ] γ]γ]
87Sr
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
F=5/2
F=3/2
F=5/2
F=7/2
∆=19 MHz
∆=27 MHz
γ=80 MHz
25Mg
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
1P1
3P1
31S0
41S0
quench laser462 nm
γ = 4 MHz
3
2
1
4
Ω12, Γ1
Ω23, Γ2
γeff 31Hz
24Mg
Γ3
T.E. Mehlstäubler et al., J.O.B 5, p.183 (2003)
ILaser
3
2
Γ
Γ∝
3
2
231
Γ
Ω+Γ=Γeff
2
3
2
232233
Γ
Ω×= ρρ
33312222 Γ+Γ=Γ ρρρ eff
for s3 <<1:
462 nm
457 nm
llll/2
Mg ovenT ~ 410 °C
detection
(PMT)
Mg beam
interaction zones
retro reflector
excitation
31S0
33P1
41S0llll/2
Search for the quenching transitionSearch for the quenching transition
σ+
σ-
J=1
J=0
J=0
σ-
σ+
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
457nm
462nm
→ 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
0
10
20
30
40
50
60
Tra
nsfe
r E
ffic
ien
cy [
%]
PQuench
[mW] per beam
(larger power @ 457nm)
0 200 400 600 800 1000
0
10
20
30
40
50
60
Tra
nsfe
r E
ffic
ien
cy [
%]
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
31D2
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
31S0
31P1
80 MHz
-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
1
2
3
4
5
6
7
8
PIR
= 1.3 mW
σ = 16 MHz
PIR
= 44 mW
σ = 26 MHz
UV
co
unts
e6/s
detuning of 881 nm laser [MHz]
Resonance in MOT
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
31D2
loss3P1,2
31S0
31P1
2-Photon resonances in 2-Photon resonances in 2424MgMg
resonances in 1D molasses resonances in 1D molasses
2-Photon resonances in 2-Photon resonances in 2424MgMg
resonances in 1D molasses resonances in 1D molasses
60 80 100 120 1402
4
6
8
10
12
14
ν (IR) in MHz
T [
mK
]
scan7b
26 mK 21 mK
30 45 60 75 90 105 1200
5
10
15
20
25
T [
mK
]
ν (IR) in MHz
Temperature across 2-photon resonance
2-Photon resonances in 2-Photon resonances in 2424MgMg
ρ33
ρ22
Populations in excited states
fi force at UV transition:
2-Photon resonances in 2-Photon resonances in 2424MgMg
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-4 -2 2 4
-40000
-20000
20000
40000
-3 -2 -1 1 2 3
-40000
-20000
20000
40000
-3 -2 -1 1 2 3
-40000
-20000
20000
40000
-2 -1 1 2
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-4 -2 2 4
-40000
-20000
20000
40000
-4 -2 2 4
-40000
-20000
20000
40000
-2 -1 1 2
-40000
-20000
20000
40000
-2 -1 1 2
-40000
-20000
20000
40000
-3 -2 -1 1 2 3
-40000
-20000
20000
40000
-2 2 4
-40000
-20000
20000
40000
-4 -2 2 4
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
-6 -4 -2 2 4 6
-40000
-20000
20000
40000
ρ22
UV
UV UV
IR
• positive feedback on faster atoms (bunching)
• higher friction for low velocities
v[m/s]
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-3 -2 -1 1 2
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-2 -1 1 2
-5000
5000
10000
15000
20000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-2 -1 1
-10000
-5000
5000
10000
15000
20000
25000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-3 -2 -1 1 2 3
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-2 -1 1 2
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-2 -1 1 2
-5000
5000
10000
15000
20000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-2 -1 1 2
-5000
5000
10000
15000
20000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-3 -2 -1 1 2 3
-20000
-10000
10000
20000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003 0.004
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.002 -0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-20000
-10000
10000
20000
30000
-0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
-4 -2 2 4
-10000
10000
20000
30000
-0.001 0.001 0.002 0.003
0.005
0.01
0.015
0.02
0.025
0.03
• force at UV transitionfi dv = a(v) dt
• integrating eqs. of motion• TOF after 100µs molasses
-4 -2 2 4
-20000
-10000
10000
20000
-0.004 -0.002 0.002
0.005
0.01
0.015
0.02
0.025
0.03
T < 100 µK ?
e.g. for balanced molasses
2-Photon resonances in 2-Photon resonances in 2424MgMg
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
-100
-75
-50
-25
25
50
75
100
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
fiber
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
Det.
400 mW @ 914 nm
160 mW @ 457 nm
PPKTP crystal
w2
w1
Cavity:Hänsch-Couillaud lock
Frequency doublingFrequency doubling