Levitated Ferromagnetic Torsional Oscillators for High-Precision Magnetometry and Probing Exotic Interactions

Abstract

Levitated ferromagnetic systems are expected to have significant potential in precision magnetic field sensing by leveraging mechanical isolation to minimize mechanical contact and associated noise. Here, we report the implementation of a high-sensitivity magnetometer based on a levitated ferromagnetic torsion oscillator, incorporating a centroid tracking method for superior measurement resolution and noises reduction. The device, featuring a compact sensor volume of $(2.5 \, \rm{mm})^3$ and operating under room temperature, attains a remarkable magnetic sensitivity of {$391\pm 59 \, \rm{fT\cdot Hz^{-1/2}}$}. This capability enables precise detection of weak magnetic fields and provides a novel platform for exploring exotic interactions beyond the Standard Model. These results demonstrate that the levitated torsion oscillator system not only serves as a powerful tool for high-precision magnetic sensing but also holds promise for advancing breakthroughs in fundamental physics.

Figures (4)

• Figure 1: Diagram of the FMTO system. (a) FMTO consists a levitating-magnet, a glass rod and a sensing magnet. A pyroly graphite disk is used to stabilize the FMTO. The motion information of the FMTO can be extracted by the camera and centroid algorithm. The insert shows a typical gap of 0.5 mm between the lifting-magnet and the graphite disk. (b) The principle of the FMTO involves the introduction of a bias magnetic field and a signal magnetic field using two independent pairs of coils. (c) The linear fit depicted in the insert, illustrating the linear fit between the squared resonance frequency and the current in the DC coil, which confirms that the orange resonant peak on the right side corresponds to the torsional mode of FMTO.
• Figure 2: Calibration of magnetic sensitivity. (a) The PSD of the laser spot's movement on the CCD is measured while the FMTO is driven by a magnetic signal. (b) The magnetic sensitivity is derived using the calibration magnetic signal. The blue line represents the PSD of the FMTO without any driving. The inset illustrates the relationship between magnetic sensitivity and frequency, particularly near torsional resonance. While the orange line represents the noise floor of the FMTO, which is limited by the measurement noise.
• Figure 3: Optimal Magnetic sensitivity under typical bias field for versus the sensor's radius. $(a)$ The potential sensitivity of FMTO magnetometer versus the sensor's radius. $(b)$ FMTO magnetometer for probing the pesudo-magnetic field generated by vibrating nucleon source.
• Figure 4: The best bound of coupling constant $f^{4+5}$. experimental result are shown as shaded in gray color above solid lines: I.ding2020, II.wu2023, III.diguang2023, IV.piegsa2012, V.kim2018. The red solid line VI gives the best bound for the FMTO realized in this work with optimal setup. The red dashed lines plot the upper bounds set by optimized FMTO magnetometers, limited by thermal torque noise, for various bias magnetic fields.