Observation of anisotropic superfluid density in an artificial crystal | ARC Centre of Excellence in Future Low-Energy Electronics Technologies

Ian Spielman, Joint Quantum Institute

We experimentally and theoretically investigate the anisotropic speed of sound of an atomic superfluid (SF) Bose-Einstein condensate in a 1D optical lattice. Because the speed of sound derives from the SF density, this implies that the SF density is itself anisotropic. We find that the speed of sound is decreased by the optical lattice, and the SF density is concomitantly reduced. This reduction is accompanied by the appearance of a zero entropy normal fluid in the purely Bose condensed phase.

The reduction in SF density—first predicted [A.~J.~Leggett, Phys. Rev. Lett. {\bf 25} 1543–1546 (1970)] in the context of supersolidity—results from the coexistence of superfluidity and density modulations, but is agnostic about the origin of the modulations. We additionally measure the moment of inertia of the system in a scissors mode experiment, demonstrating the existence of rotational flow. As such we shed light on some supersolid properties using imposed, rather than spontaneously formed, density-order.

About the presenter

Ian Spielman is a Fellow of the Joint Quantum Institute (JQI), a joint research institute between the National Institute of Standards and Technology (NIST) and the University of Maryland (UMd). A member of the NIST technical staff since 2006, in 2014 Spielman was appointed as a “NIST Fellow” (of NIST’s 1,800 member technical staff, just 40 are NIST fellows).

Spielman is an experimentalist in atomic, molecular and optical physics but was trained as a condensed matter physicist during his Ph.D. at Caltech from 1998 to 2004. Spielman’s research centers on using ultracold-atom systems – just 10’s of nano-Kelvin above absolute zero – to realize many-body phenomena so common in conventional materials as well as analogues to high energy and cosmological physics. He has pioneered techniques to add artificial magnetic fields and spin-orbit coupling to cold-atom systems opening the door for new many-body systems. Spielman has received many awards on account of this research including the 2015 APS I.I. Rabi Prize in Atomic, Molecular, and Optical Physics.