arXiv subjects

Sotatsu Otabe

Publications and source records attributed to Sotatsu Otabe.

8 recordsLinked to original sources

arXiv2026

Time-of-flight force sensing below the quantum zero-point fluctuation

Sensing weak forces through observing a mechanical motion near or below its quantum zero-point fluctuation has been desired in diverse areas. While mechanical oscillators have played a crucial role in such studies, their application to free-fall-type sensing has been elusive, in particular in the quantum regime. Here, we demonstrate sensing a static force of the order of 10 zeptonewtons with a levitated nanomechanical oscillator below the zero-point fluctuation through the rapid modulation of its confining potential. We prepare a squeezed state with a reduced velocity uncertainty by abruptly decreasing the potential. Subsequently, we detect the exerted static force through time-of-flight measurements, where we release the nanoparticle from the potential and measure the displacement during a free fall. Furthermore, time-of-flight measurements allow us to perform quantum state tomography of the squeezed state, from which we reconstruct its Wigner quasiprobability distribution and evaluate the Fisher information for the position measurement to quantify the achievable force sensitivity of our protocol. Our results demonstrate that modulating the trap stiffness serves as a crucial technique for quantum-limited force sensing and paves the way to utilize a levitated nanoparticle as a promising sensing platform beyond the quantum limit with a capability of quantum state tomography.

quant-ph↗

arXiv2025

Observation of an Optical Spring in a Robustly Controlled Signal-Recycled Michelson Interferometer

We present, to the best of our knowledge, the first demonstration of an optical spring in a signal-recycled Michelson interferometer without arm cavities. The setup utilizes multiple laser fields to achieve stable and precisely controllable detuning and incorporates a compliant suspension system comprising two double-spiral springs. These results support optical spring-enhanced interferometers with intracavity amplification, offering a promising avenue for improving high-frequency sensitivity in future gravitational-wave detectors.

physics.optics↗

arXiv2025

Sensitivity Enhancement in Atom-Interferometer Gyroscopes via Phase-Modulation Signal Readout Scheme

Quantum sensors based on atom interferometers are advancing both fundamental physics and practical applications, with higher sensitivity being a key requirement for these investigations. Here, we experimentally demonstrate a sensitivity enhancement of an atom-interferometer gyroscope using a phase-modulation signal readout scheme. Phase modulation applied to the laser light used for atomic state manipulation is transferred to the atomic phase and read out via multi-harmonic demodulation. The observed sensitivity improvement factor of $1.20\pm0.04$ over the conventional phase sweep scheme agrees with theoretical predictions. We also found that phase-dispersion compensation control, which compensates atomic velocity dispersion and preserves interference contrast at high angular rates, effectively eliminates the nonlinearity inherent in multi-harmonic demodulation. The sensitivity improvement achieved by our method is applicable to a broad class of atom interferometers and requires no modifications to the optical or vacuum systems, making it particularly effective for size-constrained applications such as large-baseline experiments and inertial navigation systems.

physics.atom-ph↗

arXiv2025

Closed-loop measurements in an atom interferometer gyroscope with velocity-dependent phase-dispersion compensation

Atom interferometer-based gyroscopes are expected to have a wide range of applications due to their high sensitivity. However, their dynamic range is limited by dephasing caused by velocity-dependent Sagnac phase shift in combination with the longitudinal velocity distribution of the atoms, restricting measurements of large angular velocities. In this study, we present a method for restoring the contrast deterioration in angular velocity measurements with interferometer gyroscopes using atomic beams. Our findings show that by introducing the pseudo-rotation effect with appropriate two-photon detunings for Raman lights in the interferometer, it is possible to effectively cancel the Sagnac phase shift for all atoms in the velocity distribution of the beam. Consequently, the contrast is unaffected by the rotation. Furthermore, we applied this method to an interferometer gyroscope with counter-propagating atomic beams sharing the same Raman lights. It is found that the angular velocity of the system can be estimated through the detuning point where the phase difference between the two interferometers is zero. This approach ensures that the scale factor of the atom interferometer gyroscope is independent of the change in the longitudinal velocity distribution of the atomic beam. We demonstrate our technique using the interferometer gyroscope of thermal atomic beams of rubidium-87, achieving a measurement of angular velocity of $\mathrm{{1.0}^{\circ}/s}$ even with an acceleration of 0.68$\mathrm{m/s^2}$ on a three-axis rotation table. This simple and robust dispersion compensation method with Raman light detuning benefits dynamic angular velocity measurements in field applications such as the inertial navigation of vehicles.

physics.atom-ph↗

arXiv2025

Analyzing the sensitivity of an atom interferometer with a phase-modulation readout scheme

The sensitivity of an interferometer depends on its readout scheme. However, little attention has been paid to the readout schemes of atom interferometers from the viewpoint of their sensitivity. The difference in sensitivity between readout schemes or their optimization has not been considered in the literature. Herein we analytically calculate the sensitivities of an atom interferometer with typical readout schemes by applying the two-photon formalism, which was developed for optical interferometers to deal with quantum noise. Our calculations reveal that by using sinusoidal phase modulation, the sensitivity can surpass that obtained by the conventional phase sweeping scheme. The superiority of this phase modulation scheme for both cold and thermal atomic beams is demonstrated. In addition, we show that the phase modulation scheme is advantageous for atom-flux fluctuation and resists atom-flux drift. This study performs a general analysis of the sensitivity of atom interferometers and identifies an advantageous readout scheme.

physics.atom-ph↗

arXiv2024

Kerr-Enhanced Optical Spring

We propose and experimentally demonstrate the generation of enhanced optical springs using the optical Kerr effect. A nonlinear optical crystal is inserted into a Fabry-Perot cavity with a movable mirror, and a chain of second-order nonlinear optical effects in the phase-mismatched condition induces the Kerr effect. The optical spring constant is enhanced by a factor of $1.6\pm0.1$ over linear theory. To our knowledge, this is the first realization of optomechanical coupling enhancement using a nonlinear optical effect, which has been theoretically investigated to overcome the performance limitations of linear optomechanical systems. The tunable nonlinearity of demonstrated system has a wide range of potential applications, from observing gravitational waves emitted by binary neutron star post-merger remnants to cooling macroscopic oscillators to their quantum ground state.

quant-ph↗

arXiv2022

Photothermal effect in macroscopic optomechanical systems with an intracavity nonlinear optical crystal

Intracavity squeezing is a promising technique that may improve the sensitivity of gravitational wave detectors and cool optomechanical oscillators to the ground state. However, the photothermal effect may modify the occurrence of optomechanical coupling due to the presence of a nonlinear optical crystal in an optical cavity. We propose a novel method to predict the influence of the photothermal effect by measuring the susceptibility of the optomechanical oscillator and identifying the net optical spring constant and photothermal absorption rate. Using this method, we succeeded in precisely estimating parameters related to even minor photothermal effects, which could not be measured using a previously developed method.

quant-ph↗

arXiv2021

Improving force sensitivity by amplitude measurement of light reflected from a detuned optomechanical cavity

The measurement of weak continuous forces exerted on a mechanical oscillator is a fundamental problem in various physical experiments. It is fundamentally impeded by quantum back-action from the meter used to sense the displacement of the oscillator. In the context of interferometric displacement measurements, we here propose and demonstrate the working principle of a scheme for coherent back-action cancellation. By measuring the amplitude quadrature of the light reflected from a detuned optomechanical cavity inside which a stiff optical spring is generated, back-action can be cancelled in a narrow band of frequencies. This method provides a simple way to improve the sensitivity in experiments limited by quantum back-action without injection of squeezed light or stable homodyne readout.

quant-ph↗