Experimental Realization of One Dimensional Helium

Spatial dimension is key to the ordered behaviors a system can exhibit.  As the dimension is lowered, locally stabilizing interactions are reduced, leading to the emergence of phases of matter without purely classical analogues, e.g. spin liquids, Dirac fermions and the fractional quantum Hall effect in two-dimensions (2D). Realizing 1D platforms has been elusive, due to their inherent lack of stability, with a few notable exceptions such as spin chains and ultracold low-density gasses. The inability of such systems to exhibit long range order is essential to their universal description in terms of the Tomonaga-Luttinger liquid theory. Here we describe experimental observation and theoretical studies of this behavior using a nanoengineering approach that preplates a templated material with 1D cyclindrical pores (MCM-41) with a noble gas to reduce the spatial dimension.  The resulting excitations of the confined 4He, confirmed by neutron scattering, are qualitatively different than three and two-dimensional superfluid helium, and consistent with Quantum Monte Carlo calculations. The results can be analyzed in terms of a mobile impurity in an otherwise linear Luttinger liquid allowing for the extraction of the microscopic parameters describing the emergent quantum liquid.