Observation of the 1S0-3P0 transition in atomic ytterbium for optical clocks and qubit arrays

We report an observation of the weak 6 1S0-6 3P0 transition in (171,173)Yb as an important step to establishing Yb as a primary candidate for future optical frequency standards, and to open up a new approach for qubits using the 1S0 and 3P0 states of Yb atoms in an optical lattice.     

Doppler-free spectroscopy of the 1S0-3P0 optical clock transition in laser-cooled fermionic isotopes of neutral mercury

We report direct laser spectroscopy of the 1S0-3P0 transition at 265.6 nm in fermionic isotopes of neutral mercury in a magneto-optical trap. Measurements of the frequency against the LNE-SYRTE primary reference using an optical frequency comb yield 1 128 575 290 808.4+/-5.6 kHz in 199Hg and 1 128 569 561 139.6+/-5.3 kHz in 201Hg. The uncertainty, allowed by the observation of the Doppler-free recoil doublet, is 4 orders of magnitude lower than previous indirect determinations. Mercury is a promising candidate for future optical lattice clocks due to its low sensitivity to blackbody radiation.     

Spectroscopy of the 1S0-3P0 clock transition of 87Sr in an optical lattice

We report on the spectroscopy of the 5s(2) 1S0(F=9/2)-->5s5p 3P0(F=9/2) clock transition of 87Sr atoms (natural linewidth of 1 mHz) trapped in a one-dimensional optical lattice. Recoilless transitions with a linewidth of 0.7 kHz as well as the vibrational structure of the lattice potential were observed. By investigating the wavelength dependence of the carrier linewidth, we determined the magic wavelength, where the light shift in the clock transition vanishes, to be 813.5+/-0.9 nm.     

Observation of the 1S0-->3P0 clock transition in 27Al+

We report, for the first time, laser spectroscopy of the 1S0-->3P0 clock transition in 27Al+. A single aluminum ion and a single beryllium ion are simultaneously confined in a linear Paul trap, coupled by their mutual Coulomb repulsion. This coupling allows the beryllium ion to sympathetically cool the aluminum ion and also enables transfer of the aluminum's electronic state to the beryllium's hyperfine state, which can be measured with high fidelity. These techniques are applied to measure the clock transition frequency nu=1,121,015,393,207,851(6) Hz. They are also used to measure the lifetime of the metastable clock state tau=20.6+/-1.4 s, the ground state 1S0 g factor gS=-0.000,792,48(14), and the excited state 3P0 g factor gP=-0.001,976,86(21), in units of the Bohr magneton.     

Observation of the ~1S_0-~3P_0 optical clock transition in cold ~(199)Hg atoms

We report on the observation of the highly forbidden ~1S_0–~3P_0 optical clock transition in laser-cooled ~(199) Hg atoms.More than 95% depletion of cold ~(199)Hg atoms is detected in the magneto-optical trap. Using the free-of-field detection method, the AC Stark shift from the cooling laser is removed from the in-field spectroscopy. At low-power clock laser pumping, the linewidth of the clock spectroscopy is approximately 450 k Hz(full width at half-maximum), which corresponds to a Doppler broadening at the atom temperature of 60 μK. We determine the ~1S_0–~3P_0transition frequency to be 1,128,575,290.819(14) MHz by referencing with a hydrogen maser and measuring with a fiber optical frequency comb. Moreover, a weak Doppler-free signal is observed.     

Isotopic shift in the3P1-3P0 Mg transition

High precision frequency measurements of the³ P ₁-³ P ₀ transitions have been performed for the three natural abundant Mg-isotopes in a metastable atomic beam. A second order hyperfine theory for two-electron atoms allows the determination of the centre-of-gravity for²⁵Mg and then the evaluation of the isotopic shift displacements. The high resolution frequency measurements (10^?8) show a noticeable departure of the total shift from a linear dependence with respect to the atomic mass.     

High-resolution isotope shift measurement of the MgI 1 S 0 - 3 P 1 intercombination transition

We measured the isotope shift of the MgI intercombination line 3s3p ³ P ₁-3s ^{2 1} S ₀ (=457 nm) for the three stable isotopes ²⁴Mg, ²⁵Mg and ²⁶Mg. The measurement was performed by optical Ramsey spectroscopy (respectively saturation spectroscopy for ²⁵Mg) on a magnesium atomic beam. The rf precision of the measurement was achieved by using optical sideband techniques for the stabilization and tuning of a dye laser relative to an ultrastable cavity.     

我国基准光钟及其绝对频率测量

光钟能够产生高稳定、高准确的光学频率,在时间频率计量、基础物理研究、相对论大地测量等领域有着潜在的应用。中国光钟研究从21世纪初开始起步,在超稳激光产生、量子参考体系制备、系统频移评估和绝对频率测量等方面取得了长足的进步,目前已经有多个研究组的光钟系统频率不确定度进入10^-18量级,多个机构实现了光钟绝对频率测量,并且有三种光钟的测量结果被国际时间频率咨询委员会采纳。文章将回顾中国为应对秒定义变革而开展的高准确度光钟及其绝对频率测量研究,梳理目前取得的进展和成果,总结存在的问题,并对未来发展提出建议。     

Hanle lifetime measurements of SrI 1P1 and CaI 1P1 levels excited by a neutral beam of 1 1S0 helium atoms

A 0.8 keV He(1 ¹S₀) beam was used to coherently excite the ¹P₁ levels of Sr and Ca targets. The coherence appears as an alignment of the excited state with respect to the beam axis. We report here the results of a Hanle measurement, or a zero-field level-crossing experiment, performed on these coherently excited levels. The radiative lifetimes of the SrI ¹P₁ and CaI ¹P₁ levels were measured to be 4.7 ns and 5.3 ns, respectively. These values are in good agreement with conventional Hanle measurements.     

Experimental determination of the helium 2(3)P(1)-1(1)S0 transition rate

We present the first experimental determination of the 2(3)P(1)-1(1)S0 transition rate in helium and compare this measurement with theoretical quantum-electrodynamic predictions. The experiment exploits the very long (approximately 1 minute) confinement times obtained for atoms magneto-optically trapped in an apparatus used to create a Bose-Einstein condensate of metastable (2(3)S1) helium. The 2(3)P(1)-1(1)S0 transition rate is measured directly from the decay rate of the cold atomic cloud following 1083 nm laser excitation from the 2(3)S1 to the 2(3)P1 state, and from accurate knowledge of the 2(3)P1 population. The value obtained is 177+/-8 s(-1), which agrees very well with theoretical predictions, and has an accuracy that compares favorably with measurements for the same transition in heliumlike ions higher in the isoelectronic sequence.     

Analysis of the blackbody-radiation shift in an ytterbium optical lattice clock

We accurately evaluate the blackbody-radiation shift in a171 Yb optical lattice clock by utilizing temperature measurement and numerical simulation. In this work. three main radiation sources are considered for the blackbody-radiation shift, including the heated atomic oven, the warm vacuum chamber, and the room-temperature vacuum windows. The temperatures on the outer surface of the vacuum chamber are measured during the clock operation period by utilizing seven calibrated temperature sensors. Then we infer the temperature distribution inside the vacuum chamber by numerical simulation according to the measured temperatures. Furthermore, we simulate the temperature variation around the cold atoms while the environmental temperature is fluctuating. Finally, we obtain that the total blackbody-radiation shift is -1.289(7)Hz with an uncertainty of 1.25×10~(-17) for our ~(171)Yb optical lattice clock. The presented method is quite suitable for accurately evaluating the blackbody-radiation shift of the optical lattice clock in the case of lacking the sensors inside the vacuum chamber.     

CW ultraviolet saturation spectroscopy of the 6p 3P0-9s 3S1 transition in mercury at 246.5 nm

We have measured the even isotope structure of the 6p ³P₀-9s ³S₁ transition in mercury at 246.5 nm using saturated absorption spectroscopy with radiation produced as the sum frequency of a 363.8 nm argon ion laser and an LD700 ring dye laser in ADP. This is the first use of cw sum-frequency mixing in nonlinear laser spectroscopy in the ultraviolet. No previous cw Doppler-free measurements have been reported at wavelenghts below 294.5 nm     

Isotopic shift measurement of the 3P1-3P0 fine structure transition of 24Mg and 26Mg

The isotopic frequency shift for the ³P₁-³P₀Δm_j=0 fine structure transition in the first metastable triplet of ²⁴Mg and ²⁶Mg is reported. The transitions corresponding to the two even isotopes of Mg have been observed via the fluorescence emission at 4571 Å of the intercombination line ³P₁-¹P₀ in a metastable atomic beam. The center frequencies have been measured with an uncertainty of 7×10^-9; the isotopic shift turned out to be 1706 ± 2 kHz.     

Direct frequency comb measurements of absolute optical frequencies and population transfer dynamics

A phase-stabilized femtosecond laser comb is directly used for high-resolution spectroscopy and absolute optical frequency measurements of one- and two-photon transitions in laser-cooled 87Rb atoms. Absolute atomic transition frequencies, such as the 5S1/2 F=2-->7S1/2 F"=2 two-photon resonance measured at 788,794 768,921 (44) kHz, are determined without a priori knowledge about their values. Detailed dynamics of population transfer driven by a sequence of pulses are uncovered and taken into account for the measurement of the 5P states via resonantly enhanced two-photon transitions.     

Theoretical calculation of the quadratic Zeeman shift coefficient of the 3P0o clock state for strontium optical lattice clock

In the weak-magnetic-field approximation, we derived an expression of quadratic Zeeman shift coefficient of $^3P^{\rm o}_0$ clock state for $^{88}$Sr and $^{87}$Sr atoms. By using this formula and the multi-configuration Dirac-Hartree-Fock theory, the quadratic Zeeman shift coefficients were calculated. The calculated values $C_2$ = $-23.38(5)$ MHz/T$^2$ for $^{88}$Sr and the $^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm9/2$ clock states for $^{87}$Sr agree well with the other available theoretical and experimental values, especially the most accurate measurement recently. In addition, the calculated values of the $^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm9/2$ clock states were also determined in our $^{87}$Sr optical lattice clock. The consistency with measurements verifies the validation of our calculation model. Our theory is also useful to evaluate the second-order Zeeman shift of the clock transition, for example, the new proposed $^1S_0$, $F = 9/2$, $M_F = \pm5/2$-${}^3P^{\rm o}_0$, $F = 9/2$, $M_F = \pm3/2$ transitions.     

A diode laser spectrometer at 634nm and absolute frequency measurements using optical frequency comb

This paper reports that two identical external-cavity-diode-laser (ECDL) based spectrometers are constructed at 634 nm referencing on the hyperfine B-X transition R(80)8-4 of ¹²⁷I₂. The lasers are stabilized on the Doppler-free absorption signals using the third-harmonic detection technique. The instability of the stabilized laser is measured to be 2.8×10^-12 (after 1000 s) by counting the beat note between the two lasers. The absolute optical frequency of the transition is, for the first time, determined to be 472851936189.5 kHz by using an optical frequency comb referenced on the microwave caesium atomic clock. The uncertainty of the measurement is less than 4.9 kHz.     

Direct excitation of the forbidden clock transition in neutral 174Yb atoms confined to an optical lattice

We report direct single-laser excitation of the strictly forbidden (6s2)1S0 <--> (6s6p)3P0 clock transition in 174Yb atoms confined to a 1D optical lattice. A small (approximately 1.2 mT) static magnetic field was used to induce a nonzero electric dipole transition probability between the clock states at 578.42 nm. Narrow resonance linewidths of 20 Hz (FWHM) with high contrast were observed, demonstrating a resonance quality factor of 2.6 x 10(13). The previously unknown ac Stark shift-canceling (magic) wavelength was determined to be 759.35 +/- 0.02 nm. This method for using the metrologically superior even isotope can be easily implemented in current Yb and Sr lattice clocks and can create new clock possibilities in other alkaline-earth-like atoms such as Mg and Ca.     

类镁离子3s21S0-3s3p1P1(Z=15～103)光谱跃迁的能级和跃迁几率的相对论多组态计算

利用全相对论性多组态Dirac-Fock平均能级(MCDF-AL)方法系统地计算 了高离化类镁离子3s21S0-3s3p1P1(Z=15～103)跃迁的能级间隔和 跃迁几率，计算中考虑了重要的核有限体积效应，Breit修正和QED修正，所得结果和最近的 实验数据及其它理论计算值进行了比较。