arXiv subjects

Naohiro Okamoto

Publications and source records attributed to Naohiro Okamoto.

5 recordsLinked to original sources

arXiv2026

Direct loading of a Sr magneto-optical trap from a thermal atomic beam

We demonstrate direct loading of a strontium (Sr) magneto-optical trap (MOT) from a thermal atomic beam in a single-chamber vacuum system. The MOT operates without a Zeeman slower, a slowing laser, a two-dimensional MOT, or differential pumping, while the entire system is maintained in the ultra-high-vacuum regime by a single ion pump. At an oven temperature of $395\,\mathrm{{}^\circ C}$, the MOT captures up to $10^{7}$ ${}^{88}\mathrm{Sr}$ atoms with a loading rate of $10^{7}\,\mathrm{atoms\,s^{-1}}$, while sustaining a background gas pressure of $1 \times 10^{-9} \,\mathrm{Torr}$. At this oven temperature, the MOT lifetime limited by collisions with background gas is $\sim 5 \,\mathrm{s}$, with the atom number primarily constrained by light-assisted two-body collisions. Eliminating differential pumping and precooling stages significantly reduces the system's size, weight, and power requirements, providing a robust and practical platform for field-deployable and spaceborne optical lattice clocks, as well as a variety of other applications requiring compact ultracold atom sources.

physics.atom-ph↗

arXiv2026

Direct Measurement of the $5s5p\,{}^1P_1 \to 5s4d\,{}^1D_2$ Decay Rate in Strontium

We report the first direct experimental determination of the branching ratio of the $5s4d\,{}^1D_2 \to 5s5p\,{}^3P_2$ transition and the decay rate of the $5s5p\,{}^1P_1 \to 5s4d\,{}^1D_2$ transition in neutral strontium. For more than four decades, these quantities lacked an experimental determination independent of theoretical input. We measure the branching ratio to be $0.177(4)$, significantly lower than the widely cited theoretical value of $0.322$ [C. W. Bauschlicher Jr. {\it et al.}, J. Phys. B \textbf{18}, 1523 (1985)]. We also determine the decay rate to be $5.3(5)\times10^3\,\mathrm{s^{-1}}$, consistent with the value reported by Hunter [L. R. Hunter {\it et al.}, Phys. Rev. Lett. \textbf{56}, 823 (1986)] but substantially lower than the recent theoretical prediction of $9.25(40)\times10^3\,\mathrm{s^{-1}}$ [A. Cooper {\it et al.}, Phys. Rev. X \textbf{8}, 041055 (2018)]. These measurements provide an experimental benchmark for quantitative modeling of loss processes in laser cooling and single-atom fluorescence detection in optical tweezers with Sr.

physics.atom-ph↗

arXiv2025

Analyzing the optical pumping on the $5s4d\,{}^1D_2-5s8p\,{}^1P_1$ transition in a magneto-optical trap of Sr atoms

We explore the efficacy of optical pumping on the $5s4d\,{}^1D_2 - 5s8p\,{}^1P_1$ ($448\,\mathrm{nm}$) transition in a magneto-optical trap (MOT) of Sr atoms. The number of trapped atoms is enhanced by a factor of $12.0(6)$ relative to the case without repumping light, which is six times as large as that obtained using the pumping transition $5s4d\,{}^1D_2 - 5s6p\,{}^1P_1$ ($717\,\mathrm{nm}$). This enhancement is limited by decay pathways that bypass the $5s4d\,{}^1D_2$ state, namely $5s5p\,{}^1P_1 \to 5s4d\,{}^3D_1 \to 5s5p\,{}^3P_0$ and $5s5p\,{}^1P_1 \to 5s4d\,{}^3D_2 \to 5s5p\,{}^3P_2$, which account for 8% of the total loss of the trapped atoms. We determine the decay rates for the $5s5p\,{}^1P_1 \to 5s4d\,{}^3D_1$ and $5s5p\,{}^1P_1 \to 5s4d\,{}^3D_2$ transitions to be $66(6)\,\mathrm{s^{-1}}$ and $2.4(2)\times10^2\,\mathrm{s^{-1}}$, respectively. Furthermore, we experimentally demonstrate for the first time that, when the trap beam diameter is small, escape of atoms in the $5s4d\,{}^1D_2$ state, which has a relatively long lifetime of $400\,\mathrm{μs}$, becomes a dominant loss mechanism, and that the $448\,\mathrm{nm}$ pumping light effectively suppresses this escape. Our findings will contribute to improved laser cooling and fluorescence imaging in cold strontium atom platforms, such as quantum computers based on optical tweezer arrays.

physics.atom-ph↗

arXiv2024

Limitation of single-repumping schemes for laser cooling of Sr atoms

We explore the efficacy of two single-repumping schemes, $5s5p \,{}^3P_2 - 5p^2 \,{}^3P_2$ ($481\,\mathrm{nm}$) and $5s5p \,{}^3P_2 - 5s5d \,{}^3D_2$ ($497\,\mathrm{nm}$), for a magneto-optical trap (MOT) of Sr atoms. We reveal that the enhancement in the MOT lifetime is limited to $26.9(2)$ for any single-repumping scheme. Our investigation indicates that the primary decay path from the $5s5p \,{}^1P_1$ state to the $5s5p \,{}^3P_0$ state proceeds via the $5s4d \,{}^3D_1$ state, rather than through the upper states accessed by the single-repumping lasers. We estimate that the branching ratio for the $5s5p \,{}^1P_1 \to 5s4d \,{}^3D_1 \to 5s5p \,{}^3P_0$ decay path is $1:3.9 \times 10^6$ and the decay rate for the transition from the $5s5p \,{}^1P_1$ state to the $5s4d \,{}^3D_1$ state is $83(32)\,\mathrm{s^{-1}}$. This outcome underscores the limitation on atom number in the MOT for long loading times ($\gtrsim 1 \,\mathrm{s}$) when employing a single-repumping scheme. These findings will contribute to the construction of field-deployable optical lattice clocks.

physics.atom-ph↗

arXiv2021

Birefringent atomic vapor laser lock in a hollow cathode lamp

We report a robust method of stabilizing a laser to the frequency of an atomic transition using a hollow cathode lamp. In contrast to the standard dichroic atomic vapor laser lock (DAVLL) method, which uses dichroism induced by a longitudinal magnetic field, we employ birefringence induced by a transversal magnetic field. We applied this method to the $(5s^2)\ {}^{1}S_{0} - (5s5p)\ {}^{1}P_{1}$ transition (461 nm) of Sr. Although the hollow cathode is made of ferromagnetic material, we successfully applied a magnetic field of sufficient strength to obtain an error signal with a theoretical maximum slope. This method may be applied to other hollow cathode lamps of different atomic species.

physics.atom-ph↗