arXiv subjects

Akio Kawasaki

Publications and source records attributed to Akio Kawasaki.

At least 19 recordsLinked to original sources

arXiv2026

Improved systematic uncertainty evaluation of the $^{171}$Yb optical lattice clock NMIJ-Yb1 with uncertainty of $2.6\times10^{-17}$

We report a systematic uncertainty evaluation of the $^{171}$Yb optical lattice clock NMIJ-Yb1 (NMIJ: National Metrology Institute of Japan) with a fractional frequency uncertainty of $2.6\times10^{-17}$, improved by a factor of 3.8 compared with our previous uncertainty. The uncertainty of the lattice light shift is reduced to $1.6\times10^{-17}$ by preparing axially sideband-cooled atoms in a shallow optical lattice. Different models to calculate the lattice light shift are compared, taking account of possible model-dependent biases due to the treatment of the radial motion of atoms trapped in the optical lattice. The uncertainty of the blackbody radiation shift reaches $7.0\times10^{-18}$ by measuring the radiative temperature at the position of atoms with an in-vacuum temperature sensor. We also demonstrate the nearly continuous operation of NMIJ-Yb1 with an uptime of 91.3 $\%$ for 10 days, showing the potential for future improvement of the calibration uncertainty of International Atomic Time.

physics.atom-ph↗

arXiv2026

Low-lying $D$ states in yttrium and actinium ions highly sensitive to variation of the fine structure constant

Whether fundamental constants vary over time or space is one of the key questions in metrology and cosmology. Among them, variation of the fine structure constant $α$ is intensively investigated. Yttrium ions Y$^+$ and actinium ions Ac$^+$ have low-lying $D$ states that are suitable for this search, with a proper path for laser cooling and detection. Theoretical calculations show that the sensitivities of the transitions between the ground state and the lowest $^3D_1$ states are $K=9.40$ and $K=9.73$, respectively. By driving the transition between the ground state and the $^3D_1$ states with a two-photon transition, the transition can be used for a high-sensitivity search for time variation of the fine structure constant. The high efficiency of a detection scheme using the transition between the $7s6d~^3D_1$ states and the $7s7p~^3P_0$ state also suggests that Ac$^+$ ions are potentially useful as a platform for quantum information processing.

physics.atom-ph↗

arXiv2025

Quantum Sensing Using Atomic Clocks for Nuclear and Particle Physics

Technologies for manipulating single atoms have advanced drastically in the past decades. Due to their excellent controllability of internal states, atoms serve as one of the ideal platforms as quantum systems. One major research direction in atomic systems is the precise determination of physical quantities using atoms, which is included in the field of precision measurements. One of such precisely measured physical quantities is energy differences between two energy levels in atoms, which is symbolized by the remarkable fractional uncertainty of $10^{-18}$ or lower achieved in the state-of-the-art atomic clocks. Two-level systems in atoms are sensitive to various external fields and can, therefore, function as quantum sensors. The effect of these fields manifests as energy shifts in the two-level system. Traditionally, such shifts are induced by electric or magnetic fields, as recognized even before the advent of precision spectroscopy with lasers. With high-precision measurements, tiny energy shifts caused by hypothetical fields weakly coupled to ordinary matter or by small effects mediated by massive particles can be potentially detectable, which are conventionally dealt with in the field of nuclear and particle physics. In most cases, the atomic systems as quantum sensors have not been sensitive enough to detect such effects. Instead, experiments searching for these interactions have placed constraints on coupling constants, except in a few cases where effects are predicted by the Standard Model of particle physics. Nonetheless, measurements and searches for these effects in atomic systems have led to the emergence of a new field of physics.

physics.atom-ph↗

arXiv2025

Improved absolute frequency measurement of $^{171}$Yb at NMIJ with uncertainty below $2\times10^{-16}$

We report improved absolute frequency measurement of the $^{1}$S$_{0}-^{3}$P$_{0}$ transition of $^{171}$Yb at National Metrology Institute of Japan (NMIJ) by comparing the $^{171}$Yb optical lattice clock NMIJ-Yb1 with 13 Cs primary frequency standards via International Atomic Time from August 2021 to May 2023. The measured absolute frequency is 518 295 836 590 863.62(10) Hz with a fractional uncertainty of $1.9\times10^{-16}$, in good agreement with the recommended frequency of $^{171}$Yb as a secondary representation of the second. This uncertainty is 2.6 times lower than our previous measurement uncertainty, and slightly lower than any uncertainties of the absolute frequency measurements of $^{171}$Yb that have so far been reported by other institutes. We also estimate correlation coefficients between our present and previous measurements, which is important for updating the recommended frequency.

physics.atom-ph↗

arXiv2024

Measurement of transition frequencies and hyperfine constants of molecular iodine at 520.2 nm

We measured the transition frequencies of the hyperfine components in the four lines (P(34) 39-0, R(36) 39-0, P(33) 39-0, and R(35) 39-0) of the B-X transitions of molecular iodine at 520.2 nm. The 520.2 nm laser was generated by wavelength-converting the output of a 1560.6 nm external-cavity diode laser using a dual-pitch periodically poled lithium niobate (PPLN) waveguide. The frequencies were measured by counting the heterodyne beats between the laser stabilized at the frequencies of the hyperfine components and a frequency comb synchronized with a hydrogen maser. We determined the transition frequencies of the a1 components with relative uncertainties of 1*10-11; the uncertainty was limited by the impurity of the molecular iodine in the cell. From the measured hyperfine splitting frequencies, we calculated the hyperfine constants of these four transitions to obtain the rotational dependence of the excited-state hyperfine constants.

physics.chem-ph↗

arXiv2024

Isotope-shift analysis with the $4f^{14}6s^{2}~^1S_0- 4f^{13}5d6s^{2}(J=2)$ transition in ytterbium

Measurements of isotope shifts have recently been attracting considerable attention due to their potentials in searching for new forces. We report on the isotope shifts of the $4f^{14}6s^{2}~^1S_0- 4f^{13}5d6s^{2}(J=2)$ transition at 431 nm in Yb, based on absolute frequency measurements with an accuracy of $\sim10$ kHz. With these data, the hyperfine constants for $^{173}$Yb are determined. To analyze these data further, electronic structure of ytterbium is theoretically calculated. The nuclear charge radii are estimated together with some previously reported isotope-shift data for other transitions. An analysis of the King plot for the $4f^{14}6s^{2}~^1S_0- 4f^{13}5d6s^{2}(J=2)$ transition shows a good consistency with other transitions, resulting in a constraint on the existence of new bosons mediating the force between an electron and a neutron. The analysis motivates further precision measurements on isotope shifts of the narrow-linewidth transitions in ytterbium, not only for the even-mass isotopes but also for the odd-mass isotopes.

physics.atom-ph↗

arXiv2024

Generation of a precise time scale assisted by a near-continuously operating optical lattice clock

We report on a reduced time variation of a time scale with respect to Coordinated Universal Time (UTC) by steering a hydrogen-maser-based time scale with a near-continuously operating optical lattice clock. The time scale is generated in a post-processing analysis for 230 days with a hydrogen maser with its fractional frequency stability limited by a flicker floor of $2\times10^{-15}$ and an Yb optical lattice clock operated with an uptime of 81.6 $\%$. During the 230-day period, the root mean square time variation of our time scale with respect to UTC is 0.52 ns, which is a better performance compared with those of time scales steered by microwave fountain clocks that exhibit root mean square variations from 0.99 ns to 1.6 ns. With the high uptime achieved by the Yb optical lattice clock, our simulation implies the potential of generating a state-of-the-art time scale with a time variation of $<0.1$ ns over a month using a better hydrogen maser reaching the mid $10^{-16}$ level. This work demonstrates that a use of an optical clock with a high uptime enhances the stability of a time scale.

physics.atom-ph↗

arXiv2024

Observation of the $4f^{14}6s^{2}~^1S_0- 4f^{13}5d6s^{2}(J=2)$ clock transition at 431 nm in $^{171}$Yb

We report on the observation of the $4f^{14}6s^{2}~^1S_0- 4f^{13}5d6s^{2}(J=2)$ transition at 431 nm in $^{171}$Yb by depleting atoms in a magneto-optical trap formed by the $6s^{2}~^1S_0-6s6p~^3P_1$ intercombination transition. The absolute frequency of the transition to the $F=3/2$ state is determined to be $695~171~054~858.1(8.2)$~kHz against physical realization of Coordinated Universal Time maintained by the National Metrology Institute of Japan with a frequency comb. The $g$ factor of the transition to the $F=3/2$ state and the A hyperfine constant are measured to be $g_J=1.54(13)$ and 1123.354(13)~MHz, respectively. More precise spectroscopy of this transition can lead to searches for time variation of the fine structure constant and searches for new physics with isotope shift measurements.

physics.atom-ph↗

arXiv2023

Tracking a nonrelativistic charge with an array of Rydberg atoms

Charged particle tracking has played a key role in the development of particle physics, particularly for understanding phenomena involving short-lived particles precisely. As a platform for high-resolution charged particle tracking, an array of Rydberg atoms is theoretically analyzed. Utilizing the Ramsey sequence to accumulate the phase shift between the ground and a Rydberg excited state induced by the time-dependent Stark shift due to a moving charge, a nonrelativistic charged particle can be tracked with a precision of $\sim10$ nm, with a potential of higher resolution by optimizing reconstruction algorithm. Although a lot of technical difficulties need to be resolved, the proposed scheme can potentially serve as a charge tracker for relativistic charged particles as well. Also, this analysis can explain potential decoherence in the quantum computation with Rydberg atoms induced by residual ions and cosmic rays.

physics.atom-ph↗

arXiv2022

Search for ultralight dark matter from long-term frequency comparisons of optical and microwave atomic clocks

We search for ultralight scalar dark matter candidates that induce oscillations of the fine structure constant, the electron and quark masses, and the quantum chromodynamics energy scale with frequency comparison data between an $^{171}$Yb optical lattice clock and a $^{133}$Cs fountain microwave clock that span 298 days with an uptime of 15.4 $\%$. New limits on the couplings of the scalar dark matter to electrons and gluons in the mass range from $10^{-22}$ eV/$c^{2}$ to $10^{-20}$ eV/$c^{2}$ are set, assuming that each of these couplings is the dominant source of the modulation in the frequency ratio. The absolute frequency of the $^{171}$Yb clock transition is also determined as $518\,295\,836\,590\,863.69(28)$ Hz, which is one of the important contributions towards a redefinition of the SI second.

physics.atom-ph↗

arXiv2022

Collective Spin-Light and Light-Mediated Spin-Spin Interactions in an Optical Cavity

The interaction between an atomic ensemble and a light mode in a high-finesse optical cavity can easily reach the strong-coupling regime, where quantum effects dominate. In this regime, the interaction can be used to generate both atom-light and atom-atom entanglement. We analyze the dominant effects on the collective atomic state and the light field, and derive a unified approach that can account for atomic entanglement induced both by measurements on the light field, and by ignoring the state of the light field altogether. We present analytical expressions for the entanglement induced by the interaction, and determine the conditions that maximize the entanglement-induced gain over the standard quantum limit in quantum sensors and atomic clocks.

quant-ph↗

arXiv2022

Librational Feedback Cooling

Librational motion, whereby a rigid body undergoes angular oscillation around a preferred direction, can be observed in optically trapped, silica microspheres. We demonstrate the cooling of one librational degree of freedom for $\sim 5~μ$m diameter spheres that have been induced to rotate with an external electric field coupled to their electric dipole moment. Cooling is accomplished by adding a phase modulation to the rotating field. The degree of cooling is quantified by applying a $π/2$ shift to the phase of the electric field and fitting the resulting exponential decay of the librational motion to obtain a damping time, as well as estimating a mode temperature from the observed libration in equilibrium. The result is an important step in the study of the dynamics of trapped microspheres, crucial to cooling the mechanical motion to its ground state, as well as providing insights regarding the charge mobility in the material at microscopic scales.

physics.optics↗

arXiv2022

Evidence of Two-Source King Plot Nonlinearity in Spectroscopic Search for New Boson

Optical precision spectroscopy of isotope shifts can be used to test for new forces beyond the Standard Model, and to determine basic properties of atomic nuclei. We measure isotope shifts on the highly forbidden ${}^2S_{1/2} \rightarrow {}^2F_{7/2}$ octupole transition of trapped $^{168,170,172,174,176}$Yb ions. When combined with previous measurements in Yb$^+$ and very recent measurements in Yb, the data reveal a King plot nonlinearity of up to 240$σ$. The trends exhibited by experimental data are explained by nuclear density functional theory calculations with the Fayans functional. We also find, with 4.3$σ$ confidence, that there is a second distinct source of nonlinearity, and discuss its possible origin.

physics.atom-ph↗

arXiv2022

Decoherence of Atomic Ensembles in Optical Lattice Clocks by Gravity

Optical lattice clocks can now resolve the height difference below 1 mm within an atomic ensemble by means of gravitational redshift with integration over sufficient amount of time. Further improvement in the stability enables the clocks to resolve the height difference of subsystems within an atomic ensemble that is conventionally interrogated as a single coherent spin state in a single Ramsey sequence, resulting in the dephasing of the coherent spin state. This effect is observable with a clock of a stability of $\lesssim 10^{-21}$ by introducing a single-layer-resolved imaging system for a three-dimensional optical lattice, and limits the 1 s stability of the clock around $10^{-19}$ for an atomic ensemble distributing symmetrically for the three axes, which is also a signal of the decoherence. With atoms in an entangled state, this can be the first observation of the decoherence of a quantum state by a gravitational effect, and the suppression of other systematic shifts to observe this decoherence seems feasible.

quant-ph↗

arXiv2021

A background-free optically levitated charge sensor

Optically levitated macroscopic objects are a powerful tool in the field of force sensing, owing to high sensitivity, absolute force calibration, environmental isolation and the advanced degree of control over their dynamics that have been achieved. However, limitations arise from the spurious forces caused by electrical polarization effects that, even for nominally neutral objects, affect the force sensing because of the interaction of dipole moments with gradients of external electric fields. In this paper we introduce a new technique to model and eliminate dipole moment interactions limiting the performance of sensors employing levitated objects. This process leads to the first noise-limited measurement with a sensitivity of $3.3\times10^{-5}e$. As a demonstration, this is applied to the search for unknown charges of a magnitude much below that of an electron or for exceedingly small unbalances between electron and proton charges. The absence of remaining systematic biases, enables true discovery experiments, with sensitivities that are expected to improve as the system noise is brought down to or beyond the quantum limit. As a by-product of the technique, the electromagnetic properties of the levitated objects can also be measured on an individual basis.

hep-ex↗

arXiv2021

Search for non-Newtonian interactions at micrometer scale with a levitated test mass

We report on a search for non-Newtonian forces that couple to mass, with a characteristic scale of ${\sim}10~μ$m, using an optically levitated microsphere as a precision force sensor. A silica microsphere trapped in an upward-propagating, single-beam, optical tweezer is utilized to probe for interactions sourced from a nanofabricated attractor mass with a density modulation brought into close proximity to the microsphere and driven along the axis of periodic density in order to excite an oscillating response. We obtain force sensitivity of ${\lesssim}10^{-16}~\rm{N}/\sqrt{\rm{Hz}}$. Separately searching for attractive and repulsive forces results in the constraint on a new Yukawa interaction of $|α| \gtrsim 10^8$ for $λ> 10~μ$m. This is the first test of the inverse-square law using an optically levitated test mass of dimensions comparable to $λ$, a complementary method subject to a different set of systematic effects compared to more established techniques.

hep-ex↗

arXiv2020

Evidence for Nonlinear Isotope Shift in Yb$^+$ Search for New Boson

We measure isotope shifts for five Yb$^+$ isotopes with zero nuclear spin on two narrow optical quadrupole transitions ${}^2S_{1/2} \rightarrow {}^2D_{3/2}$, ${}^2S_{1/2} \rightarrow {}^2D_{5/2}$ with an accuracy of $\sim 300$ Hz. The corresponding King plot shows a $3 \times 10^{-7}$ deviation from linearity at the 3 $σ$ uncertainty level. Such a nonlinearity can indicate physics beyond the Standard Model (SM) in the form of a new bosonic force carrier, or arise from higher-order nuclear effects within the SM. We identify the quadratic field shift as a possible contributor to the nonlinearity at the observed scale, and show how the nonlinearity pattern can be used in future, more accurate measurements to separate a new-boson signal from nuclear effects.

physics.atom-ph↗

arXiv2020

High sensitivity, levitated microsphere apparatus for short-distance force measurements

A high sensitivity force sensor based on dielectric microspheres in vacuum, optically trapped by a single, upward-propagating laser beam, is described. Off-axis parabolic mirrors are used both to focus the 1064~nm trapping beam and to recollimate it to provide information on the horizontal position of the microsphere. The vertical degree of freedom is readout by forming an interferometer between the light retroreflected by the microsphere and a reference beam, hence eliminating the need for auxiliary beams. The focus of the trapping beam has a 1/e$^2$ radius of 3.2~$μ$m and small non-Gaussian tails, suitable for bringing devices close to the trapped microsphere without disturbing the optical field. Electrodes surrounding the trapping region provide excellent control of the electric field, which can be used to drive the translational degrees of freedom of a charged microsphere and the rotational degrees of freedom of a neutral microsphere, coupling to its electric dipole moment. With this control, the charge state can be determined with single electron precision, the mass of individual microspheres can be measured, and empirical calibrations of the force sensitivity can be made for each microsphere. A force noise of $<1\times10^{-17}$~N/$\sqrt{\rm Hz}$, which is comparable to previous reports, is measured on all three degrees of freedom for 4.7~$μ$m diameter, 84~pg silica microspheres. Various devices have been brought within $1.6~μ$m of the surface of a trapped microsphere. Metrology in the trapping region is provided by two custom-designed microscopes providing views in the horizontal and one of the vertical planes. The apparatus opens the way to performing high sensitivity three-dimensional force measurements at short distance.

physics.ins-det↗