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European Quantum Electronics Conference (EQEC)

Laser cooling and quantum jumps of a single indium ion

E. Peik, Guenter Hollemann, HERBERT WALTHER

Published Aug 24, 2005• 2 citations
Publisher

Abstract

We performed laser spectroscopy of ${\mathrm{In}}^{+}$ ions stored in a radio-frequency trap. The 5${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}5s5p $^{3}$${\mathit{P}}_{1}$ transition at 230.6 nm was excited and its hyperfine splitting and isotope shift have been measured. The lifetime of the $^{3}$${\mathit{P}}_{1}$ state was measured using intensity modulated laser excitation: \ensuremath{\tau}${(}^{3}$${\mathit{P}}_{1}$)=0.44(4) \ensuremath{\mu}s. A single indium ion was laser cooled using this intercombination line and dark periods in the fluorescence were observed when the metastable $^{3}$${\mathit{P}}_{0}$ state was populated by a magnetic dipole decay from $^{3}$${\mathit{P}}_{1}$. The radiative lifetime of the forbidden transition $^{3}$${\mathit{P}}_{0}$${\ensuremath{\rightarrow}}^{1}$${\mathit{S}}_{0}$ was determined from the duration of the dark periods: \ensuremath{\tau}${(}^{3}$${\mathit{P}}_{0}$)=0.14(2) s. This value is compared to calculations based on perturbation theory. Prospects for an optical frequency standard using the narrow 5${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}5s5p $^{3}$${\mathit{P}}_{0}$ resonance at 236.5 nm of a single laser-cooled indium ion are discussed.

DOI
10.1109/eqec.1994.698036

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Laser cooling and quantum jumps of a single indium ion

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We performed laser spectroscopy of ${\mathrm{In}}^{+}$ ions stored in a radio-frequency trap. The 5${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}5s5p $^{3}$${\mathit{P}}_{1}$ transition at 230.6 nm was excited and its hyperfine splitting and isotope shift have been measured. The lifetime of the $^{3}$${\mathit{P}}_{1}$ state was measured using intensity modulated laser excitation: \ensuremath{\tau}${(}^{3}$${\mathit{P}}_{1}$)=0.44(4) \ensuremath{\mu}s. A single indium ion was laser cooled using this intercombination line and dark periods in the fluorescence were observed when the metastable $^{3}$${\mathit{P}}_{0}$ state was populated by a magnetic dipole decay from $^{3}$${\mathit{P}}_{1}$. The radiative lifetime of the forbidden transition $^{3}$${\mathit{P}}_{0}$${\ensuremath{\rightarrow}}^{1}$${\mathit{S}}_{0}$ was determined from the duration of the dark periods: \ensuremath{\tau}${(}^{3}$${\mathit{P}}_{0}$)=0.14(2) s. This value is compared to calculations based on perturbation theory. Prospects for an optical frequency standard using the narrow 5${\mathit{s}}^{2}$ $^{1}$${\mathit{S}}_{0}$\ensuremath{\rightarrow}5s5p $^{3}$${\mathit{P}}_{0}$ resonance at 236.5 nm of a single laser-cooled indium ion are discussed.

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A single laser-cooled indium ion is a promising candidate for an ultimate resolution optical time or frequency standard. It can be shown that single ions from group IIIA of the periodic table (indium, thallium, etc.) can have extremely small systematic errors. In addition to being free from Doppler, transit-time and collisional shifts, these ions are also quite insensitive to perturbations from ambient magnetic and electric fields (mainly due to the use of a J=0-0 transition for spectroscopy). Of all group IIIA ions, indium seems to be the most practical, since it is heavy enough to have a tolerable intercombination cooling transition rate and (unlike thallium) has transitions which are easily accessible with frequency multiplied continuous-wave lasers. A single indium ion standard has a potential inaccuracy of one part in 10(exp 18) for integration times of 10(exp 6) seconds. We have made substantial progress during the grant period in constructing a frequency standard based upon a single indium ion. At the beginning of the grant period, single indium ions were being successfully trapped, but the lasers and optical systems were inadequate to achieve the desired goal. We have considerably improved the stability of the dye laser used to cool the ions and locked it to a molecular resonance line, making it possible to observe stable cooling-line fluorescence from a single indium ion for reasonable periods of time, as required by the demands of precision spectroscopy. We have substantially improved the single-ion fluorescence signal with significant benefits for the detection efficiency of forbidden transitions using the 'shelving' technique. Finally, we have constructed a compact, efficient UV 'clock' laser and observed 'clock' transitions in single indium ions using this laser system. We will elaborate on these accomplishments.

•Jan 1, 2001•0 citations
We performed laser spectroscopy of In+{\mathrm{In}}^{+}In+ ions stored in a radio-frequency trap. The 5s2{\mathit{s}}^{2}s2 ^{1}$${\mathit{S}}_{0}\ensuremath{\rightarrow}5s5p ^{3}$${\mathit{P}}_{1} transition at 230.6 nm was excited and its hyperfine splitting and isotope shift have been measured. The lifetime of the ^{3}$${\mathit{P}}_{1} state was measured using intensity modulated laser excitation: \ensuremath{\tau}{(}^{3}$${\mathit{P}}_{1})=0.44(4) \ensuremath{\mu}s. A single indium ion was laser cooled using this intercombination line and dark periods in the fluorescence were observed when the metastable ^{3}$${\mathit{P}}_{0} state was populated by a magnetic dipole decay from ^{3}$${\mathit{P}}_{1}. The radiative lifetime of the forbidden transition ^{3}$${\mathit{P}}_{0}$${\ensuremath{\rightarrow}}^{1}$${\mathit{S}}_{0} was determined from the duration of the dark periods: \ensuremath{\tau}{(}^{3}$${\mathit{P}}_{0})=0.14(2) s. This value is compared to calculations based on perturbation theory. Prospects for an optical frequency standard using the narrow 5s2{\mathit{s}}^{2}s2 ^{1}$${\mathit{S}}_{0}\ensuremath{\rightarrow}5s5p ^{3}$${\mathit{P}}_{0} resonance at 236.5 nm of a single laser-cooled indium ion are discussed.
We performed laser spectroscopy of In+{\mathrm{In}}^{+}In+ ions stored in a radio-frequency trap. The 5s2{\mathit{s}}^{2}s2 1^{1}1S0{\mathit{S}}_{0}S0​\ensuremath{\rightarrow}5s5p 3^{3}3P1{\mathit{P}}_{1}P1​ transition at 230.6 nm was excited and its hyperfine splitting and isotope shift have been measured. The lifetime of the 3^{3}3P1{\mathit{P}}_{1}P1​ state was measured using intensity modulated laser excitation: \ensuremath{\tau}(3{(}^{3}(3P1{\mathit{P}}_{1}P1​)=0.44(4) \ensuremath{\mu}s. A single indium ion was laser cooled using this intercombination line and dark periods in the fluorescence were observed when the metastable 3^{3}3P0{\mathit{P}}_{0}P0​ state was populated by a magnetic dipole decay from 3^{3}3P1{\mathit{P}}_{1}P1​. The radiative lifetime of the forbidden transition 3^{3}3P0{\mathit{P}}_{0}P0​${\ensuremath{\rightarrow}}^{1}$S0{\mathit{S}}_{0}S0​ was determined from the duration of the dark periods: \ensuremath{\tau}(3{(}^{3}(3P0{\mathit{P}}_{0}P0​)=0.14(2) s. This value is compared to calculations based on perturbation theory. Prospects for an optical frequency standard using the narrow 5s2{\mathit{s}}^{2}s2 1^{1}1S0{\mathit{S}}_{0}S0​\ensuremath{\rightarrow}5s5p 3^{3}3P0{\mathit{P}}_{0}P0​ resonance at 236.5 nm of a single laser-cooled indium ion are discussed.
The ${5s}^{2}{}^{1}{S}_{0}\ensuremath{\rightarrow}5s5p{}^{3}{P}_{0}$ transition of a single laser-cooled 115In+{}^{115}{\mathrm{In}}^{+}115In+ ion in a miniature radiofrequency trap is investigated as a possible optical frequency standard. This line at a frequency of 1267 THz (wavelength 236.5 nm) is highly immune to frequency shifts due to external perturbations so that the expected systematic uncertainties can be reduced to the millihertz level. Experimentally, we obtained a fractional resolution $\ensuremath{\Delta}\ensuremath{\nu}/\ensuremath{\nu}=1.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ (linewidth 170 Hz), limited by the frequency instability of the laser used for excitation. The g factor and the lifetime of the metastable 3P0{}^{3}{P}_{0}3P0​ level were measured as ${g(}^{3}{P}_{0})=\ensuremath{-}9.87(5)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ and $\ensuremath{\tau}{(}^{3}{P}_{0})=0.195(8) \mathrm{s}.$ Both values are in good agreement with perturbative calculations, based on hyperfine mixing between the 1P{}^{1}P1P and 3P{}^{3}P3P levels.
Single ions trapped and laser cooled provide ideal objects for high resolution spectroscopy and frequency standards. For the latter purpose we are investigating the 5s2 1S0 → 5s5p 3P0 transition of In+. With a natural linewidth of only 1.1 Hz this resonance offers very high resolution and is highly immune to frequency shifts due to external electromagnetic fields, because it connects two levels with vanishing electronic magnetic momenta [1]. The wavelength of this clock transition is 236.5 nm and is technically very convenient, since it coincides with the fourth harmonic of the 946 nm Nd:YAG laser line. So this intrinsically frequency stable solid-state laser can be used to excite the transition [2]. For laser cooling and fluorescence detection of the indium ion the 5s2 1So -> 5s5p 3P1 transition at 230.6 nm can be employed. The use of the relatively narrow intercombination line for laser cooling allows us to study optical sideband cooling in the strong binding regime, where the oscillation frequencies of the ion in the trap (around 1 MHz) are larger than the optical linewidth of 360 kHz. In this parameter range laser cooling is possible to the quantum ground state of the vibrational motion in the trap corresponding to a temperature of roughly 100 μK. The same low temperature was obtained with sideband cooling of a small Coulomb crystal consisting of two ions, creating an interesting new quantum few-particle system.
A single Sr+ atom was confined in a radio-frequency quadrupole trap and laser cooled with resonant laser light. Examination of the transition Doppler profile indicated an ion kinetic temperature of less than 500 mK. Quantum jumps into and out of the metastable 4d(2)D(5/2) level were observed by laser excitation on the electric-quadrupole-allowed transition from the ground state at 674 nm. The dark and bright periods in the strong fluorescence showed variations owing to the applied driving field on the electric-quadrupole transition. These results provide an improved determination of tau = 372 +/- 25 msec for the natural metastable-state lifetime.
We are investigating the 5s/sup 21/S/sub 0//spl rarr/5s5p/sup 3/P/sub 0/ transition of a single trapped laser-cooled /sup 115/In/sup +/ ion as a possible optical frequency standard. This line with a natural linewidth of only 1.1 Hz, corresponding to a Q factor of 1.2/spl middot/10/sup 15/, is highly immune to systematic frequency shifts due to external perturbations. For sideband laser cooling and fluorescence detection of the indium ion the 5s/sup 21/S/sub 0//spl rarr/5s5p/sup 3/P/sub 1/ transition at 230.6 nm is excited. Temperatures below 100 /spl mu/K and a mean vibrational quantum number<1 of the ion in the trap have been reached. For the clock transition a resolution of 3/spl middot/10/sup -13/ (linewidth 350 Hz) has been obtained so far, limited by the laser linewidth. The absolute frequency of the /sup 1/S/sub 0//spl rarr//sup 3/P/sub 0/ transition was measured by making a link to known reference frequencies of molecular iodine and methane using a frequency chain.
A single laser-cooled indium ion is a promising candidate for an ultimate resolution optical time or frequency standard. It can be shown that single ions from group IIIA of the periodic table (indium, thallium, etc.) can have extremely small systematic errors. In addition to being free from Doppler, transit-time and collisional shifts, these ions are also quite insensitive to perturbations from ambient magnetic and electric fields (mainly due to the use of a J=0-0 transition for spectroscopy). Of all group IIIA ions, indium seems to be the most practical, since it is heavy enough to have a tolerable intercombination cooling transition rate and (unlike thallium) has transitions which are easily accessible with frequency multiplied continuous-wave lasers. A single indium ion standard has a potential inaccuracy of one part in 10(exp 18) for integration times of 10(exp 6) seconds. We have made substantial progress during the grant period in constructing a frequency standard based upon a single indium ion. At the beginning of the grant period, single indium ions were being successfully trapped, but the lasers and optical systems were inadequate to achieve the desired goal. We have considerably improved the stability of the dye laser used to cool the ions and locked it to a molecular resonance line, making it possible to observe stable cooling-line fluorescence from a single indium ion for reasonable periods of time, as required by the demands of precision spectroscopy. We have substantially improved the single-ion fluorescence signal with significant benefits for the detection efficiency of forbidden transitions using the 'shelving' technique. Finally, we have constructed a compact, efficient UV 'clock' laser and observed 'clock' transitions in single indium ions using this laser system. We will elaborate on these accomplishments.