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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 a ^{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} 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 toward a redefinition of the second in the International System of Units.

We report improved frequency ratio measurement with $^{87}$Sr and $^{171}$Yb optical lattice clocks at the National Metrology Institute of Japan (NMIJ). The $^{87}$Sr optical lattice clock is enhanced with several major modifications and is re-evaluated with a reduced uncertainty of $1.1\times10^{-16}$. We employed a $^{171}$Yb optical lattice clock with an uncertainty of $4\times10^{-16}$ that was developed for contributing to International Atomic Time (TAI). The measurement result is $\nu_{\mathrm{Yb}}/\nu_{\mathrm{Sr}}$ = 1.207 507 039 343 338 58(49)$_{\mathrm{sys}}$(6)$_{\mathrm{stat}}$ with a fractional uncertainty of $4.1\times10^{-16}$, which is 3.4 times smaller than our previous measurement result., Comment: 8 pages, 6 figures, 1 table

We report the status on an Yb optical lattice clock that was designed to run for a long-term operation towards contribution to the International Atomic Time (TAI) regularly. Nearly continuous operation of the Yb clock was realized with 90% uptime over several weeks. This enables to reduce the uncertainty in the link between the Yb clock and TAI to the low 10−16 level.

We evaluate the uncertainty of our Sr optical lattice clock at the 10 -17 level, through robust clock operation with assistance of optical frequency combs. This clock will be operated for contribution to the International Atomic Time.

We demonstrate a second harmonic generation (SHG) of 116 mW at 461 nm in a periodically poled lithium niobate waveguide when the power of the 922 nm fundamental light is coupled into the waveguide was 350 mW. The waveguide is 12.5 μm wide, 12.0 μm thick, 22 mm long, and has a 1 mm long slab window at the output facet of the waveguide. The temperature acceptance bandwidth of the phase-matching curve of the SHG is approximately 0.5 °C. The SHG system demonstrates good beam quality and is reliable for cold atom experiments, including research on optical lattice clocks.

Waveguide-based devices are essential for highly efficient nonlinear optical conversion. However, the nonlinearity associated with the conversion in such devices is not self-evident. The authors present a method using optical frequency metrology to reveal the nonlinearity inside a waveguide, and establish that the spectral broadening in a periodically poled lithium niobate waveguide is due to quadratic nonlinearity. They also demonstrate absolute frequency measurement using the generated ultrabroadband comb. This study will contribute to the design of chip-scale, fully integrated devices for efficient nonlinear optical conversion.

We report the status of our 171Yb optical lattice clock. The frequency stability of the Yb lattice clock is $1\times10^{-14}(\tau$/s)-1/2 where $\tau$ is an averaging time. The systematic uncertainty of the Yb lattice clock is evaluated to be $3.6\times10^{-16}$. Towards contribution to the International Atomic Time, some contrivances are incorporated in order for the Yb lattice clock to run for a long term. For example, automatic relocking schemes are recently prepared for phase locking and injection locking.

We report an uncertainty evaluation of an $^{171}$Yb optical lattice clock with a total fractional uncertainty of $3.6\times10^{-16}$, which is mainly limited by the lattice-induced light shift and the blackbody radiation shift. Our evaluation of the lattice-induced light shift, the density shift, and the second-order Zeeman shift is based on an interleaved measurement where we measure the frequency shift using the alternating stabilization of a clock laser to the $\mathrm{6s^{2}\,^{1}S_{0}-6s6p\,^{3}P_{0}}$ clock transition with two different experimental parameters. In the present evaluation, the uncertainties of two sensitivity coefficients for the lattice-induced hyperpolarizability shift $d$ incorporated in a widely-used light shift model by RIKEN and the second-order Zeeman shift $a_{\mathrm{Z}}$ are improved compared with the uncertainties of previous coefficients. The hyperpolarizability coefficient $d$ is determined by investigating the trap potential depth and the light shifts at the lattice frequencies near the two-photon transitions $\mathrm{6s6p^{3}P_{0}-6s8p^{3}P_{0}}$, $\mathrm{6s8p^{3}P_{2}}$, and $\mathrm{6s5f^{3}F_{2}}$. The obtained values are $d=-1.1(4)$ $\mathrm{\mu}$Hz and $a_{\mathrm{Z}}=-6.6(3)$ Hz/mT$^{2}$. These improved coefficients should reduce the total systematic uncertainties of Yb lattice clocks at other institutes.

We report an uncertainty evaluation of an

Frequency offset locking between two Nd:YAG lasers is performed using frequency locking with an electrical delay line. The relative frequency instability of the offset locking is measured to be 3.5×10−12 for an averaging time of 1 s, which is approximately 77 times smaller than that of the free-running case. The frequency instability of the frequency locking is compared to that of the phase locking between the two Nd:YAG lasers. Furthermore, a compact solid-state laser is frequency locked to an optical frequency comb with a frequency instability of 8.2×10−11 for an averaging time of 1 s, which is improved by approximately 20 times, with respect to the free-running case. The offset-locking scheme using a delay line is useful for various applications including a research on quantum optics, interferometric measurements, and experiments involving laser cooling, such as an optical lattice clock.

We have developed an optical lattice clock that can operate in dual modes: a strontium (Sr) clock mode and an ytterbium (Yb) clock mode. Dual-mode operation of the Sr-Yb optical lattice clock is achieved by alternately cooling and trapping $^{87}$Sr and $^{171}$Yb atoms inside the vacuum chamber of the clock. Optical lattices for Sr and Yb atoms were arranged with horizontal and vertical configurations, respectively, resulting in a small distance of the order of 100 $\mu$m between the trapped Sr and Yb atoms. The $^{1}$S$_{0}$-$^{3}$P$_{0}$ clock transitions in the trapped atoms were interrogated in turn and the clock lasers were stabilized to the transitions. We demonstrated the frequency ratio measurement of the Sr and Yb clock transitions by using the dual-mode operation of the Sr-Yb optical lattice clock. The dual-mode operation can reduce the uncertainty of the blackbody radiation shift in the frequency ratio measurement, because both Sr and Yb atoms share the same blackbody radiation., Comment: 6 pages,5 figures

We develop a compact frequency-stabilized laser at 1064 nm for wavelength conversion in long-distance quantum communication. Linewidth and frequency stability are demonstrated to be sufficient to connect nitrogen-vacancy centers in diamond in remote nodes.

We generate a broadband frequency comb using a WG-PPLN and measure the offset frequency of the comb by using a frequency-stabilized laser at 532 nm. The visible comb is generated through χ(2) process.

We demonstrate a compact frequency-stabilized laser at 1064 nm using Doppler-free saturation absorption spectroscopy of molecular iodine. The achieved laser frequency stability and linewidth are 5.7 10-12 (corresponding to an uncertainty of the laser frequency of 1.6 kHz) and 400 kHz, respectively. The developed frequency-stabilized laser can be used as a pump laser for wavelength conversion from visible to telecom (or vice versa) to connect quantum memories utilizing nitrogen-vacancy centers in diamond at remote nodes in fiber-based quantum communication., Comment: 5 pages, 6 figures, JOSAB accepted

We developed a mode-locked Er fiber laser containing a small optical bench. The electro-optic modulator on the bench is used to control the repetition frequency at a high speed together with a piezoelectric transducer.

We have developed iodine-stabilized lasers using ultra-compact diode laser modules at 531, 561 and 594 nm. The achieved frequency stabilities were typically 4×10−13 at an averaging time of 1000 s.

We have developed an 8-branch frequency comb using 3 stages of fiber couplers for frequency stabilization of multiple lasers. A Ti:Sapphire laser is frequency-stabilized to the comb and evaluated in regard to the frequency stability.

We demonstrate an 8-branch Er:fiber frequency comb with seven application ports, which can be individually optimized for applications with different wavelengths. The beat between the comb and a cw laser has a signal-to-noise ratio exceeding 30 dB at a resolution bandwidth of 300 kHz. The 8-branch frequency comb is used to perform frequency locking for four repumping and lattice lasers, and the frequency measurement of two clock lasers of strontium and ytterbium optical lattice clocks. We have achieved reliable optical lattice clock operation, thanks to the stable frequency locking and measurement obtained by using the 8-branch frequency comb. The developed frequency comb is a powerful experimental tool for various applications, including not only optical lattice clocks, but also research on quantum optics that use many frequency-stabilized lasers.

We demonstrate high-resolution spectroscopy of molecular iodine using coin-sized laser modules at 531 nm, 561 nm, and 594 nm. Hyperfine components of the R(36)32-0, P(64)20-0, and P(69)12-1 transitions are observed with a signal-to-noise ratio of several tens over a bandwidth of 100 Hz. The laser modules are frequency-stabilized to the observed hyperfine components and achieve stabilities at a level of 10−12 for a 1-s averaging time. The frequency-stabilized coin-sized laser modules are useful for various applications, including interferometric measurements and studies of molecular iodine.

We demonstrate a mode-locked Er:fiber laser with a compact fiber-pigtailed optical bench containing a free-space electro-optic modulator for high-speed feedback control. The achieved servo bandwidth of the beat frequency between a given comb component and a reference laser is approximately 850 kHz. The realization of a narrow-linewidth and highly stable frequency comb is confirmed by measuring both in-loop and out-of-loop beat frequencies. We also demonstrate the frequency measurement of two iodine-stabilized Nd:YAG lasers through the narrow-linewidth comb without stability degradation. The developed optical frequency comb can work continuously for weeks without maintenance.

We demonstrate high-precision spectroscopy of molecular iodine using ultra-compact diode laser modules at 531, 561 and 594 nm. Entire hyperfine structures of iodine lines are obtained with a linewidth of a few MHz.