1. Characterization of Superfluid Helium Dynamics Using Nanoparticles Daniel Lathrop, University of Maryland College Park, DMR 1407472 For the first time, researchers at the University of Maryland, College Park have visually observed the formation of waves caused by the twisting of vortices in quantum superfluids, i.e., fluids that as so cold that the particles behave according to the rules of quantum mechanics. Liquid Helium exhibits an exotic state of matter below 2.17 Kelvin where quantum-mechanical effects are manifested at macroscopic scales. This superfluid exhibits peculiar bulk properties such as flow without resistance, similar to how a superconductor conducts electrical currents without resistance. One key feature of superfluid Helium is the presence of quantized vortices - a quantum fluid analogue to a tornado or bathtub-drain vortex – which can display a tangled state called quantum turbulence. Of particular interest is vortex reconnection, a violent event which occurs when two vortices cross and exchange tails. Vortex reconnection produces significantly different dynamics than in any familiar fluid. Predicted by Richard Feynman in 1955, these vortices have only recently been directly observed by a techniques our lab developed using frozen Hydrogen as tracer particles or fluorescent nanoparticles at the nanometer scale. Artist rendition of reconnection exciting travelling helical Kelvin waves on quantized vortex cores in superfluid helium. Our observation of this event was featured in the Proceedings of the National Academy. Image by Enrico Fonda. “Direct observation of Kelvin waves excited by quantized vortex reconnection.” Proc Natl Acad Sci USA 111:4707–4710 (2014).

2. Characterization of Superfluid Helium Dynamics Using Nanoparticles Daniel Lathrop, University of Maryland College Park, DMR 1407472 This research serves both to better understand the properties of this strange form of quantum matter and to educate a new generation of scholars in condensed matter experiments, including undergraduate mentoring and graduate student training. Understanding turbulence in quantum fluids, such as ultracold helium, can help us to better understand everything from superconductors to neutron stars. Superconductors, which are materials that conduct electricity without resistance below certain temperatures, develop quantum vortices. Understanding the behavior of vortices may help researchers develop superconductors that can remain superconducting under less extreme conditions. The undergraduate research team June 2012. Robby Blum (left) and Julia Salevan (2 nd from left), currently graduate students at Yale University, graduated with High Honors in Physics Spring 2012. Tyler Holland-Ashford, at Harvey-Mudd College, spent the 2012 summer in our REU program. The public appreciation of science is a critical component of ensuring our nation’s strength in science and technology. In support of public appreciation of science the research team offers lab tours to a very broad range of audiences: middle school girls (annual), high school groups, undergraduate clubs, prospective students, visiting faculty, visiting government staff and science journalists. In addition the team offers short pedagogical videos, posted on the research group YouTube channel (www.youtube.com/user/n3umh), which has more than 117,000 views to datewww.youtube.com/user/n3umh