Optical trapping of nanoparticles in superfluid helium

Abstract

Optical tweezers, the three-dimensional confinement of a nanoparticle by a strongly focused beam of light, have been widely employed in investigating biomaterial nanomechanics, nanoscopic fluid properties, and ultrasensitive detections in various environments such as inside living cells, at gigapascal pressure, and under high vacuum. However, the cryogenic operation of solidstate-particle optical tweezers is poorly understood. In this study, we demonstrate the optical trapping of metallic and dielectric nanoparticles in superfluid helium below 2 K, which is two orders of magnitude lower than in the previous experiments. We prepare the nanoparticles via in-situ laser ablation.The nanoparticles are stably trapped with a single laser beam tightly focused in the superfluid helium. Our method provides a new approach for studying nanoscopic quantum hydrodynamic effects and interactions between quantum fluids and classical objects.Teaser Optical tweezers can grab nanoparticles at extremely low temperature (1.4 K), show-1

Visualisation of quantised vortex reconnection as enabled by laser ablation

“…Laser ablation, or sputtering, is a unique in-situ preparation method to produce atoms, ions, and nano/microparticles in various environments; it is also applicable to superfluid 4 He. Laser ablation in superfluid 4 He has been used for precision spectroscopy[1-3], tracer injection [20], nano/micro structure formation [5,6], and optical manipulation/trapping [21,22]. In this study, we observed the silicon nanoparticledecorated, suspended quantised vortices, and identified the vortex reconnection events [13], the dynamics of which were found to be consistent with the results of dimensional analysis the simple vortex filament model (VFM) calculations.…”

“…This finding clearly supports the hypothesis that the quantised vortex plays a major role in the formation of the semiconducting or metallic nanowires in superfluid 4 He [5,12,16,18,[25][26][27], although the intermediate process needs to be further studied. The laser ablation method can inject various nanoparticles, ranging from semiconductors [21] to metals [5,22], into superfluid 4 He.…”

“…Various material options and size controllability are significant advantages that provide an alternative method not only for the quantised vortex visualization, but also for liquid helium flow visualization. Moreover, these features are important for the incorporation of optical manipulation techniques [21,22] into quantum fluid research.…”