  We investigate experimentally the physics of quantum phase slips in
one-dimensional Josephson Junction chains. These quantum phase-slips are
induced by quantum phase fluctuations occurring on single junctions of the
chain. In our experiment we can tune the strength of these fluctuations as each
chain junction is realized in form of a SQUID leading to tunable Josephson
coupling. We determine the ground state of the chain via switching current
measurements of the chain shunted by a large Josephson junction. Our results
can be well fitted with a tight binding Hamiltonian taking into account quantum
phase-slips.
