title: Thermally activated state transition technique for femto-Newton-level force measurement.
abstract: We develop and test a thermally activated state transition technique for ultraweak force measurement. As a force sensor, the technique was demonstrated on a classical Brownian bead immersed in water and restrained by a bistable optical trap. A femto-Newton-level flow force imposed on this sensor was measured by monitoring changes in the transition rates of the bead hopping between two energy states. The treatment of thermal disturbances as a requirement instead of a limiting factor is the major feature of the technique, and provides a new strategy by which to measure other ultraweak forces beyond the thermal noise limit.
authors.affiliation: Department of Photonics and Institute of Electro-Optical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan.
authors.forename: Feng-Jung
authors.initials: FJ
authors.lastname: Chen
authors.forename: Jhih-Sian
authors.initials: JS
authors.lastname: Wong
authors.forename: Ken Y
authors.initials: KY
authors.lastname: Hsu
authors.forename: Long
authors.initials: L
authors.lastname: Hsu