  The Ising chain in transverse field is a paradigmatic model for a host of
physical phenomena, including spontaneous symmetry breaking, topological
defects, quantum criticality, and duality. Although the quasi-1D ferromagnet
CoNb$_2$O$_6$ has been put forward as the best material example of the
transverse field Ising model, it exhibits significant deviations from ideality.
Through a combination of THz spectroscopy and theory, we show that
CoNb$_2$O$_6$ in fact is well described by a different model with strong bond
dependent interactions, which we dub the {\it twisted Kitaev chain}, as these
interactions share a close resemblance to a one-dimensional version of the
intensely studied honeycomb Kitaev model. In this model the ferromagnetic
ground state of CoNb$_2$O$_6$ arises from the compromise between two distinct
alternating axes rather than a single easy axis. Due to this frustration, even
at zero applied field domain-wall excitations have quantum motion that is
described by the celebrated Su-Schriefer-Heeger model of polyacetylene. This
leads to rich behavior as a function of field. Despite the anomalous domain
wall dynamics, close to a critical transverse field the twisted Kitaev chain
enters a universal regime in the Ising universality class. This is reflected by
the observation that the excitation gap in CoNb$_2$O$_6$ in the ferromagnetic
regime closes at a rate precisely twice that of the paramagnet. This originates
in the duality between domain walls and spin-flips and the topological
conservation of domain wall parity. We measure this universal ratio `2' to high
accuracy -- the first direct evidence for the Kramers-Wannier duality in
nature.
