title: Search for millicharged particles using optically levitated microspheres.
abstract: We report results from a search for stable particles with charge ≳10^{-5}e in bulk matter using levitated dielectric microspheres in high vacuum. No evidence for such particles was found in a total sample of 1.4 ng, providing an upper limit on the abundance per nucleon of 2.5×10^{-14} at the 95% confidence level for the material tested. These results provide the first direct search for single particles with charge ≲0.1e bound in macroscopic quantities of matter and demonstrate the ability to perform sensitive force measurements using optically levitated microspheres in vacuum.
authors.affiliation: Physics Department, Stanford University, Stanford, California 94305, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Moore
authors.affiliation: Physics Department, Stanford University, Stanford, California 94305, USA.
authors.forename: Alexander D
authors.initials: AD
authors.lastname: Rider
authors.affiliation: Physics Department, Stanford University, Stanford, California 94305, USA.
authors.forename: Giorgio
authors.initials: G
authors.lastname: Gratta