Highly sensitive levitated optomechanical systems can be used as precise acceleration and force sensors to search for fundamental physics. Eliminating the net charge on these systems reduces the most significant coupling to external electric fields yet leaves the issue of backgrounds created by higher order multipole moments in the charge distribution of the levitated sensors. In many high sensitivity applications of levitated optomechanical sensors, dipole induced forces can be many orders of magnitude larger than the forces of interest. Thus, techniques to measure, control, and ultimately eliminate dipole generated backgrounds may be required to realize numerous experiments such as the search for millicharged particles, the exploration of new parameter space of dark matter mass with an array of levitated microspheres and possibly future work towards detection of gravitational entanglement between micron sized masses. This talk will discuss the application of controlled precessive torques to the electric dipole moment of a levitated microsphere in vacuum to reduce dipole-induced backgrounds by 2 orders of magnitude as well as work towards integrating such sensors in large arrays.
Recent developments in optical trapping techniques in high vacuum allow micron-sized objects to be used as precise acceleration and force sensors with respective sensitivities of 100ng/sqrt(Hz) and 1aN/sqrt(Hz), making these sensors ideal to measure tiny forces and recoils which are the result of interactions with the environment. Due to single-electron control of the electric charge, these sensors can be made electrically neutral. This not only enables better isolation from electromagnetic noise, but also allows the measurement of electric charges on the order of 10^-4e. This levitated object is used in the search of new physics in regions of parameter space inaccessible by other techniques. This talk will discuss such sensor characterization and capabilities as well as recent results of searches for dark matter, millicharged particles bound to matter and projections for a search for short ranged interactions.
A single beam optical trapping system is used to trap and rotate silica and vaterite microspheres in high vacuum. Large vaterite microspheres with diameters up to 15 μm are fabricated with multi-stage precipitation reactions and are rotated in the trap through the transfer of spin angular momentum from the photons in the trapping beam to the spheres. An electro-optic modulator is used to vary the polarization of the trapping beam, allowing for control over the rotation with damping times on the order of a day and with rotation frequencies up to 10 MHz for 10 μm diameter spheres. While highly birefringent spheres are successfully trapped at moderate vacuum pressures (⪆10−2 mbar), poor reproducibility is observed for trapping spheres in high vacuum. This trapping behavior is found to be independent of the morphology, birefringence, and monodispercity of the spheres.
A single vertical laser beam is used to trap SiO2 and vaterite spheres with diameters ranging from 5 to 32um. The center of mass acceleration sensitivity for the SiO2 spheres is as low as 4 × 10−7 g/Hz−1/2 for the largest spheres. This system also allows high-bandwidth modulation of the polarization of the trapping beam, enabling control of the rotation of the microspheres. The maximum rotation speeds exceed a few MHz for both types of spheres, while the damping time exceeds several hours at 2 × 10−7 mbar. This setup can be used to measure forces and torques acting on the microspheres
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