Abstract:  In one spatial dimension it is not possible to break a continuous symmetry
due to strong fluctuations, even at zero temperature. Although fermionic
examples of quasi-one-dimensional systems abound, including carbon
nanotubes and quantum wires, it is much more difficult to reach this limit
in high density bosonic fluids due to a short coherence length on the
atomic scale.  Recent advances in nanofabrication techniques now allow for
the confinement of the quantum liquid helium-4 inside pores with nanometer
radius, but unequivocal experimental evidence of one-dimensional behavior
is still lacking. We have performed large scale numerical simulations near
the superfluid transition to investigate how the signatures of dimensional
crossover are reflected in the thermodynamic properties of nano-confined
helium-4. The results demonstrate the breakdown of the two-fluid model of
superfluidity in low dimensions and hint at the emergence of quantum
hydrodynamics inside the pore at length scales that can be probed in the
laboratory.