Keisuke Nakamura

<jats:title>Abstract</jats:title><jats:p>We have developed a Yb-doped fiber amplifier (YDFA) using fusion splicing, and characterized its performance with numerical simulation, achieving a continuous output of above <jats:inline-formula><jats:alternatives><jats:tex-math>$10~{\mathrm{W } }$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mn>10</mml:mn> <mml:mspace /> <mml:mi>W</mml:mi> </mml:math></jats:alternatives></jats:inline-formula> of <jats:inline-formula><jats:alternatives><jats:tex-math>$1064~{\mathrm{nm } }$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mn>1064</mml:mn> <mml:mspace /> <mml:mi>nm</mml:mi> </mml:math></jats:alternatives></jats:inline-formula> light. The device has been conceptualized to have a configuration as simple as possible; a strategy for using fiber amplifiers in harsh environments where quick repairs and replacements may become necessary at unexpected times.</jats:p>

<jats:p>We have realized a comb system with a 30 GHz mode spacing, 62 % available wavelength coverage in the visible region, and nearly 40 dB spectral contrast by combining a robust erbium-doped-fiber-based femtosecond laser, mode filtering with newly designed optical cavities, and broadband-visible-range comb generation using a chirped periodically-poled LiNbO<jats:sub>3</jats:sub> ridge waveguide. Furthermore, it is suggested that this system produces a spectrum with little change over 29 months. These features of our comb will contribute to fields requiring broad-mode-spacing combs, including astronomical observations, such as exoplanet exploration and the verification of the cosmic accelerating expansion.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We developed a laser frequency stabilization and an optical fiber transmission system for the the francium electric dipole moment search. The absolute accuracy of a laser frequency stabilization scheme using a state-of-the-art commercial wavelength meter was 0.48 MHz at ±2 nm and -1.33 MHz at ±200 nm from calibration wavelength, respectively, and the frequency instability is below 10<jats:sup>-9</jats:sup> with a standard deviation of 0.56 MHz over 60 hours. We also demonstrated that a 400 m long fiber laid between laboratories can transmit 30 mW of trapping laser light, which is sufficient for a magneto-optical trapping of francium. The polarization crosstalk in the fiber was stable at -25 dB over 12 hours of measurement.</jats:p>

We installed a 400-m-long polarization-maintaining fibers for magneto-optical trapping of Francium atoms. Fiber polarization stability of ~9×10^-4 was achieved with an averaging time of 10 seconds, which even allows fluorescence observation at 20 atoms.

<jats:title>Abstract</jats:title> <jats:p>We propose a method to measure the electron electric dipole moment (eEDM) using ultracold entangled francium (Fr) atoms trapped in an optical lattice, yielding an uncertainty below the standard quantum limit. Among the alkali atoms, Fr offers the largest enhancement factor to the eEDM. With a Fr based experiment, quantum sensing using quantum entangled states could enable a search for the eEDM at a level below 10<jats:sup>−30</jats:sup> <jats:italic>e</jats:italic>cm. We estimate statistical and systematic errors attached to the proposed measurement scheme based on this quantum sensing technique. A successful quantum sensing of the eEDM could enable the exploration of new physics beyond the standard model of particle physics.</jats:p>