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Optically levitated nanoparticles in vacuum are a promising model system to test physics beyond our current understanding of quantum mechanics. Such experimental tests require extreme control over the dephasing of the levitated particle's motion. If the nanoparticle carries a finite net charge, it experiences a random Coulomb force due to fluctuating electric fields. This dephasing mechanism can be fully excluded by discharging the levitated particle. Here, we present a simple and reliable technique to control the charge on an optically levitated nanoparticle in vacuum. Our method is based on the generation of charges in an electric discharge and does not require additional optics or mechanics close to the optical trap.

Stiftung Stipendien-Fonds des Verbandes der chemischen Industrie e.V.; German National Academic Foundation; Bruker; National Science Foundation (NSF CAREER) [CHE 0748226]; MOST of China [2011YQ03012406]; NSFC [21021120456]; EMRP

Optical near-fields are interesting from a theoretical perspective and of importance for practical applications, such as high-resolution imaging, sensing, and antenna-coupled quantum light sources. In this work, we use a custom-designed superconducting nanowire single-photon detector to directly read out the near-field interaction between a source and a detector. We use a subwavelength-sized aperture at the end of an optical fiber to record spatial near-field maps and to measure the distance dependence of the optical near-field interaction. Our measurements can be well described by a superposition of evanescent source fields with no noticeable probe-sample coupling. Our approach is a first step towards the development of near-field imaging techniques with single quantum sensitivity.Optical near-fields are interesting from a theoretical perspective and of importance for practical applications, such as high-resolution imaging, sensing, and antenna-coupled quantum light sources. In this work, we use a custom-designed superconducting nanowire single-photon detector to directly read out the near-field interaction between a source and a detector. We use a subwavelength-sized aperture at the end of an optical fiber to record spatial near-field maps and to measure the distance dependence of the optical near-field interaction. Our measurements can be well described by a superposition of evanescent source fields with no noticeable probe-sample coupling. Our approach is a first step towards the development of near-field imaging techniques with single quantum sensitivity.