  The Griffiths-McCoy singularity is a phenomenon characteristic of
low-dimensional disordered quantum spin systems, in which the magnetic
susceptibility shows singular behavior as a function of the external field even
within the paramagnetic phase. We study whether this phenomenon is observed in
the transverse-field Ising model with disordered ferromagnetic interactions on
the quasi-two-dimensional diluted Chimera graph both by quantum Monte Carlo
simulations and by extensive experiments on the D-Wave quantum annealer used as
a quantum simulator. From quantum Monte Carlo simulations, evidence is found
for the existence of the Griffiths-McCoy singularity in the paramagnetic phase.
The experimental approach on the quantum hardware produces results that are
less clear-cut due to the intrinsic noise and errors in the analog quantum
device but can nonetheless be interpreted to be consistent with the existence
of the Griffiths-McCoy singularity as in the Monte Carlo case. This is the
first experimental approach based on an analog quantum simulator to study the
subtle phenomenon of Griffiths-McCoy singularities in a disordered quantum spin
system, through which we have clarified the capabilities and limitations of the
D-Wave quantum annealer as a quantum simulator.
