Optical levitation and feedback cooling of a nanoparticle at subwavelength distances from a membrane

We optically trap a nanoparticle in a laser beam strongly focused on a dielectric membrane in vacuum. By investigating the motion of the trapped particle, we map the position-dependent optical potential in front of the membrane while interferometrically measuring the distance between the particle and the membrane surface. Furthermore, we demonstrate feedback cooling of the particle's motion in subwavelength proximity to the dielectric surface. The demonstrated optomechanical control of a levitated nanoparticle in close proximity of an interface at low gas pressures is an integral requirement to investigate short-range interactions in yet unexplored parameter regimes.