高精度分光を目指した CaH + の生成とトラップ
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Transcript of 高精度分光を目指した CaH + の生成とトラップ
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高精度分光を目指した CaH+
の生成とトラップ
富山大学・理 森脇喜紀
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Spectroscopy of 40CaH+
the pure vibrational transition (v=0, J=0, F=1/2, M=±1/2) → (v=1, J=0, F=1/2, M=±1/2) can potentially be measured with an uncertainty of 10-16
by use of
simultaneous trapping with Ca+ ions
sympathetic cooling
quantum logic measurement
Application to the test of the time invariance of fundamental constants e.g. electron-proton mass ratio
{ P.O.Schmidt et al.Science 309, 749(2005)
Motivation
Shelkovnikov et al. PRL100, 150801 (2008) Vibrational transition of SF6 ~ 10-14
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Proposal: High precision measurements of the pure vibrational transition of 40CaH+
• Simultaneous trapping of a 40CaH+ and a 40Ca+ in a linear trap
Long interaction time reduces the homogeneous linewidth
Ions in a crystal state inside a linear trap are free from Stark shift
Some transition frequencies of molecular ions are free from Zeeman shift
Kajita and Moriwaki J. Phys. B 42, 154022(2009)
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Estimated frequency uncertainty (order of 10-16)
CaH+ ( v = 0, J = 0, F = 1/2, M = ±1/2 ) → ( v = 1, J = 0, F = 1/2, M = ±1/2 ) transition f = 42.24 THz (7.1 m)
(1) Natural linewidth 2.5 Hz
(2) Zeeman shift (magnetic field < 1 G) < 1.3 x 10-17
(3) Stark shift induced by the trapping electric field < 10-17
(4) Electric quadrupole shift is zero because of F = 1/2
(5) Stark shift induced by probe laser light is most dominant ~ 1.2 x 10-16 with saturation power (32 mW/cm2)
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Georgiadis et al. J. Chem. Phys. 92, 7060 (1988)
2.5 eV
Production of CaH+
endothermic reaction
Ca+ (4p 2P 1/2) + H2 CaH+ + H
?
(2) Ca++H2 → CaH+ +H
(1) Laser ablation of Ca containing solids
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Laser systemTo Trap
Pump laser (397 nm)
Repump laser (866 nm)
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RF Trap
Hyperboloid electrodes
r0=7.5 mm
Vdc=0 V
Vac=350 V
Ω/2π=1.65 MHz
Dz=25 eV
Vdc+Vac cos Ωt
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LIF dependence on He pressure and qz
220
4
mr
eVq ac
z
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Temperature and size of ion cloud
Doppler width ~2 GHz
T~600 K
Δr~0.45 mmΔz~0.23 mm
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LIF decay with H2 buffer gas
LIF signal is proportional to the number of Ca+ ions.
With H2 buffer gas, LIF decay significantly.
Ca+ (4p2P1/2)+H2→CaH++H ?
Pho
ton
Cou
nts
(cps
)
Time (s)
He 4.5*10-6 Torr
H2 4.4*10-6 Torr
20000
0 500 1000 1500
10000
5000
~3600 s
~11000 s
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Q-Mass spectrum
Time (s)
mas
s si
gnal
(m
=41
)
Laser on
Laser off
0 50 100 150 200 250
0.1
0.2
0.3
0.4
0.5 Buffer gas : H2 (99.99995%)
The mass signal (m=41u) is normalized by that of m=40 u
M=41u signals appear with the laser irradiation.
With D2 buffer gas, m=42 u signals are observed.
Production of CaH+, CaD+ has been confirmed !
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Indication of some loss mechanisms of Ca+
Without 397nm and 866nm laser, LIF decays slowly.Without 866 nm laser, LIF decays fast although the 2D3/2 state is optically pumped.
Pho
ton
Cou
nts
(cps
)
Time (s)
H2 4.4*10-6 Torr
20000
397&866 laser chopped
866nm laser chopped
0 500 1000
10000
5000
Ca+ (3d 2D 3/2) + H2 CaH+ + H/
Photoassociated ion loss?
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spectroscopy of CaH+
There have been no experimental data on CaH+.
Needs for reliable theoretical data ab initio calculations of Ca+-H potential curves electric energy levels, vibrational levels, Rotational constants, transition dipole moments by M. Abe (collaborator)
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Ca+ 2S [(4s)1] + H 2S [(1s)1]
Ca+ 2D [(3d)1] + H 2S [(1s)1]
Ca+ 2P [(4p)1] + H 2S [(1s)1]
Potential energy curves
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a 4th order MBPT: Canuto et al. Phys. Rev. A. 1993. b Two-elec. valence CI and core polarization: Boutalib et al. Chem. Phys. 1992.
Spectroscopic constants of the ground state of CaH+ (11)
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Vibrational TDM in atomic unit (21)
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21
31
Absorption Emission
21S state around 400nm more than 600nm
31S state 240 nm 400 nm
21P state 240 nm 380 nm
Candidate transitions in LIF
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Conclusion• We proposed high precision measurements of the pure vibrational transition of 40CaH+
• production of CaH+ , CaD+ is confirmed
Future•laser spectroscopy of CaH+
Cryogenic ion trap:
99% of CaH+ ions are localized in the (v,J)=(0,0) state at T=4 K
H2 vapor pressure ~ 10-7 Torr
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共同研究者
• 梶田雅稔 (NICT)
• 阿部穣里 (Tokyo Metropolitan Univ.)
• 松島房和 , 小林かおり , 榎本勝成 ( 富山大学 )
小山達也 , 中口利彦 , 日比野誠 ( 学生 )