Experimental Realization of One Dimensional Helium

The realization of experimental platforms exhibiting one dimensional (1D) quantum phenomena has been elusive, due to their inherent lack of stability, with a few notable exceptions including spin chains, carbon nanotubes and ultracold low-density gasses. The difficulty of such systems in exhibiting long range order is integral to their effective description in terms of the Tomonaga-Luttinger liquid theory. Recently, it has been proposed that bosonic superfluid 4He could realize a 1D quantum system beyond the Luttinger liquid paradigm. Here we describe an experimental observation of this behavior using nanoengineering by preplating a porous material with a noble gas to enhance dimensional reduction. The resulting excitations of the confined 4He are qualitatively different than 3D and 2D superfluid helium, and can be analyzed in terms of a mobile impurity in a Luttinger liquid allowing for the characterization of the emergent quantum liquid. The confined helium system offers the possibility of tuning via pressure - from weakly interacting, all the way to the super Tonks-Girardeau gas of strongly interacting hard-core particles.