  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.
