Levitated optomechanics in the free particle limit

Abstract

Both levitated and tethered systems are excellent platforms for measuring weak interactions. While tethered systems allow for the observation of free mass behavior, they are susceptible to intermodulation effects, which do not affect levitated optomechanical systems. However, levitated systems are typically modeled as oscillators rather than free masses. We have helped fill this gap by producing a levitated optomechanical system that enables observations within the free particle limit. Leveraging the low oscillation frequencies of a magneto-gravitational trap, we employed high-speed imaging techniques to observe behaviors beyond oscillator resonance. These techniques have enabled us to achieve observations just 25 times above the standard quantum limit for a free mass, achieving a displacement sensitivity of 3 pm/square root Hz. The first use of a Bessel beam optical ruler was tested for distance calibration of a magneto-gravitational trap. With active feedback cooling, a continuous set of position data was collected with a duration of 48 h. This data was instrumental in evaluating force sensitivity for this system within the free particle limit, reaching a sensitivity of 22 yN. We devised a new mathematical method to characterize force sensitivity for a free mass subjected to stochastic noise. The advancement of these techniques and systems can serve as effective platforms for searching for dark matter candidates and testing quantum collapse models.