arXiv subjects

Yoshio Torii

Publications and source records attributed to Yoshio Torii.

13 recordsLinked to original sources

arXiv2025

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

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↗

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 $400\,\mathrm{\mu s}$, 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↗

arXiv2017

Doppler-free spectroscopy of metastable Sr atoms using a hollow cathode lamp

We report on the demonstration of Doppler-free spectroscopy of metastable Sr atoms using a hollow cathode lamp (HCL). We employed a custom Sr HCL which is filled with a mixture of 0.5-Torr Ne and 0.5-Torr Xe as a buffer gas to suppress velocity changing collisions and increase the populations in all the $(5s5p){}^3P_J(J=0,\ 1,\ 2)$ metastable states. We performed frequency-modulation spectroscopy for the $(5s5p){}^3P_0-(5s6s){}^3S_1$, $(5s5p){}^3P_1-(5s6s){}^3S_1$, $(5s5p){}^3P_2-(5s5d){}^3D_2$, and $(5s5p){}^3P_2-(5s5d){}^3D_3$ transitions with sufficient signal to noise ratios for laser frequency stabilization. We also observed the hyperfine transitions of $(5s5p){}^3P_2-(5s5d){}^3D_3$ of $^{87}\mathrm{Sr}$ . This method would greatly facilitate laser cooling of Sr.

physics.atom-ph↗

arXiv2013

Photoionization loss in simultaneous magneto-optical trapping of Rb and Sr

We demonstrate the simultaneous magneto-optical trapping (MOT) of Rb and Sr and examine the characteristic loss of Rb in the MOT due to photoionization by the cooling laser for Sr. The photoionization cross section of Rb in the $5P_{3/2}$ state at 461 nm is determined to be $1.4(1)\times10^{-17}$ cm$^2$. It is important to consider this loss rate to realize a sufficiently large number of trapped Rb atoms to achieve a quantum degenerate mixture of Rb and Sr.

physics.atom-ph↗

arXiv2013

A simplified 461-nm laser system using blue laser diodes and a hollow cathode lamp for laser cooling of Sr

We develop a simplified light source at 461 nm for laser cooling of Sr without frequency-doubling crystals but with blue laser diodes. An anti-reflection coated blue laser diode in an external cavity (Littrow) configuration provides an output power of 40 mW at 461 nm. Another blue laser diode is used to amplify the laser power up to 110 mW by injection locking. For frequency stabilization, we demonstrate modulation-free polarization spectroscopy of Sr in a hollow cathode lamp. The simplification of the laser system achieved in this work is of great importance for the construction of transportable optical lattice clocks.

physics.atom-ph↗

arXiv2012

Laser Phase and Frequency Stabilization Using Atomic Coherence

We present a novel and simple method of stabilizing the laser phase and frequency by polarization spectroscopy of an atomic vapor. In analogy to the Pound-Drever-Hall method, which uses a cavity as a memory of the laser phase, this method uses atomic coherence (dipole oscillations) as a phase memory of the transmitting laser field. A preliminary experiment using a distributed feedback laser diode and a rubidium vapor cell demonstrates a shot-noise-limited laser linewidth reduction (from 2 MHz to 20 kHz). This method would improve the performance of gas-cell-based optical atomic clocks and magnetometers and facilitate laser-cooling experiments using narrow transitions.

physics.atom-ph↗

arXiv2012

Buffer gas-assisted polarization spectroscopy of 6Li

We report on the demonstration of Doppler-free polarization spectroscopy of the D2 line of 6Li atoms. Counterintuitively, the presence of an Ar buffer gas, in a certain pressure range, causes a drastic enhancement of the polarization rotation signal. The observed dependence of the signal amplitude on the Ar buffer pressure and the pump laser power is reproduced by calculations based on simple rate equations. We performed stable laser frequency locking using a dispersion signal obtained by polarization spectroscopy for laser cooling of 6Li atoms.

physics.atom-ph↗

arXiv2007

Holographic storage of multiple coherence gratings in a Bose-Einstein condensate

We demonstrate superradiant conversion between a two-mode collective atomic state and a single-mode light field in an elongated cloud of Bose-condensed atoms. Two off-resonant write beams induce superradiant Raman scattering, producing two independent coherence gratings with a different wave vector in the cloud. By applying phase-matched read beams after a controllable delay, the gratings can be selectively converted into the light field also in a superradiant way. Due to the large cooperativity parameter and the small velocity width of the condensate, a high conversion efficiency of $> 70$ % and a long storage time of $> 120$ $μ$s were achieved.

physics.atom-ph↗

arXiv2005

Large atom number Bose-Einstein Condensate machines

We describe experimental setups for producing large Bose-Einstein condensates of 23Na and 87Rb. In both, a high flux thermal atomic beam is decelerated by a Zeeman slower and is captured and cooled in a magneto-optical trap. The atoms are then transfered into a cloverleaf style Ioffe-Pritchard magnetic trap and cooled to quantum degeneracy with radio frequency induced forced evaporation. Typical condensates contain 20 million atoms. The design includes a second vacuum chamber into which ultracold atoms can be transported with an optical tweezers. This allows the flexibility to rapidly prepare and perform a wide variety of experiments.

cond-mat.other↗

arXiv1999

Mach-Zehnder Bragg interferometer for a Bose-Einstein Condensate

We construct a Mach-Zehnder interferometer using Bose-Einstein condensed rubidium atoms and optical Bragg diffraction. In contrast to interferometers based on normal diffraction, where only a small percentage of the atoms contribute to the signal, our Bragg diffraction interferometer uses all the condensate atoms. The condensate coherence properties and high phase-space density result in an interference pattern of nearly 100% contrast. In principle, the enclosed area of the interferometer may be arbitrarily large, making it an ideal tool that could be used in the detection of vortices, or possibly even gravitational waves.

cond-mat↗