Abstract
Force sensors are at the heart of different technologies such as atomic force microscopy or inertial sensing. These sensors often rely on the measurement of the displacement amplitude of mechanical oscillators under applied force. The best sensitivity is typically achieved when the force is alternating at the mechanical resonance frequency of the oscillator, thus increasing its response by the mechanical quality factor. The measurement of low-frequency forces, that are below resonance, is a more difficult task as the resulting oscillation amplitudes are significantly lower. Here we use a single-trapped 88Sr+ ion as a force sensor. The ion is electrically driven at a frequency much lower than the trap resonance frequency. We measure small amplitude of motion by measuring the periodic Doppler shift of an atomic optical clock transition, enhanced using the quantum lock-in technique. We report frequency force detection sensitivity as low as 2.8 × 10−20 NHz−1/2.
Highlights
Force sensors are at the heart of different technologies such as atomic force microscopy or inertial sensing
Most force sensors rely on the displacement of mechanical oscillators as an estimator for the applied force
Our force detection is performed on an 88Sr þ ion trapped in a linear Paul trap with radial frequencies close to 2.3 MHz and axial frequency of 1.13 MHz, and Doppler cooled to a temperature of T 1⁄4 2 mK on a strong dipole allowed transition at 422 nm
Summary
Force sensors are at the heart of different technologies such as atomic force microscopy or inertial sensing. We measure small amplitude of motion by measuring the periodic Doppler shift of an atomic optical clock transition, enhanced using the quantum lock-in technique. Ion-trap experiments have demonstrated yocto-Newton range measurement sensitivity[2,3] of forces that were alternating at frequencies that varied between 50 and 900 kHz. Measuring forces that oscillate at frequencies much lower than this range is a challenge if one wishes to maintain the mechanical resonance condition. Periodic Doppler shifts on optical clock transitions, resulting in motional sidebands at the trap harmonic frequency, have been used for precision ion thermometry and sideband cooling. We use an optical atomic clock transition in a singletrapped 88Sr þ ion and the quantum lock-in technique for the purpose of force metrology. We demonstrate two force detection methods for two scenarios—one in which the phase of the oscillating force is known and the quantum lock-in sequence can be synchronized with it, and one where only the force frequency is known
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