arXiv subjects

Yuya Kuwahara

Publications and source records attributed to Yuya Kuwahara.

5 recordsLinked to original sources

arXiv2020

Optical trapping of the transversal motion for an optically levitated mirror

Optomechanical systems are suitable for elucidating quantum phenomena at the macroscopic scale in the sense of the mass scale. The systems should be well-isolated from the environment to avoid classical noises, which conceal quantum signals. Optical levitation is a promising way to isolate optomechanical systems from the environment. To realize optical levitation, all degrees of freedom need to be trapped. Until now, longitudinal trapping and rotational trapping of a mirror with optical radiation pressure have been studied in detail and validated with various experiments. However, less attention has been paid to the transversal trapping of a mirror. Herein, we report a pioneering result where we experimentally confirmed transversal trapping of a mirror of a Fabry-Pérot cavity using a torsional pendulum. Through this demonstration, we experimentally proved that optical levitation is realizable with only two Fabry-Pérot cavities that are aligned vertically. This work paves the way toward optical levitation and realizing a macroscopic quantum system.

quant-ph↗

arXiv2017

Optical Levitation of a Mirror for Reaching the Standard Quantum Limit

We propose a new method to optically levitate a macroscopic mirror with two vertical Fabry-P{é}rot cavities linearly aligned. This configuration gives the simplest possible optical levitation in which the number of laser beams used is the minimum of two. We demonstrate that reaching the standard quantum limit (SQL) of a displacement measurement with our system is feasible with current technology. The cavity geometry and the levitated mirror parameters are designed to ensure that the Brownian vibration of the mirror surface is smaller than the SQL. Our scheme provides a promising tool for testing macroscopic quantum mechanics.

quant-ph↗

arXiv2016

Ground Based Low-Frequency Gravitational-wave Detector With Multiple Outputs

We have developed a new gravitaional-wave (GW) detector, TOrsion-Bar Antenna (TOBA), with multiple-output configuration. TOBA is a detector with bar-shaped test masses that rotate by the tidal force of the GWs. In our detector, three independent information about the GW signals can be derived by monitoring multiple rotational degrees of freedom, i.e., horizontal rotations and vertical rotations of the bars. Since the three outputs have different antenna pattern functions, the multi-output system improves the detection rate and the parameter estimation accuracy. It is effective in order to obtain further details of the GW sources, such as population and directions. We successfully operated the multi-output detector continuously for more than 24 hours with stable data quality. Also, the sensitivity of one of the signals is improved to be $1 \times 10^{-10}$ ${\rm Hz}^{-1/2}$ at 3 Hz by the combination of the passive and active vibration isolation systems, while sensitivities to possible GW signals derived from the vertical rotations are worse than that from the horizontal rotation.

gr-qc↗

arXiv2016

Search for a stochastic gravitational wave background at 1-5 Hz with Torsion-bar Antenna

We set the first upper limit on the stochastic gravitational wave (GW) background in the frequency range of $1-5\,\mathrm{Hz}$ using a Torsion-bar Antenna (TOBA). A TOBA is a GW detector designed for the detection of low frequency GWs on the ground, with two orthogonal test masses rotated by the incident GWs. We performed a 24-hour observation run using the TOBA and set upper limits, based on frequentist statistics and Bayesian statistics. The most stringent values are $Ω_\mathrm{gw}h_0^2 \leq 6.0 \times10^{18}$ (frequentist) and $Ω_\mathrm{gw}h_0^2 \leq 1.2 \times 10^{20}$ (Bayesian) both at $2.58\,\mathrm{Hz}$, where $h_0$ is the Hubble constant in units of $100\,\mathrm{km/s/Mpc}$ and $Ω_\mathrm{gw}$ is the GW energy density per logarithmic frequency interval in units of the closure density.

gr-qc↗

arXiv2016

All-sky coherent search for continuous gravitational waves in 6-7 Hz band with a torsion-bar antenna

A torsion-bar antenna (TOBA) is a low-frequency terrestrial gravitational wave (GW) antenna which consists of two orthogonal bar-shaped test masses. We upgraded the prototype TOBA and achieved the strain sensitivity $10^{-10}$ Hz$^{-1/2}$ at around 1 Hz. We operated the upgraded TOBA (called the "Phase-II TOBA") located at Tokyo in Japan for 22.5 hours and performed an all-sky coherent search for continuous GWs using the $\mathcal{F}$-statistic. We place upper limits on continuous GWs from electromagnetically unknown sources in the frequency range from 6 Hz to 7 Hz with the first derivative of frequency less than $7.62 \times 10^{-11}$ Hz/s using data from the TOBA. As a result, no significant GW signals are found in the frequency band 6-7 Hz. The most stringent upper limit upper limit on the dimensionless GW strain with 95% confidence level in this band is $3.6 \times 10^{-12}$ at 6.84 Hz.

gr-qc↗