  Random scattering of photons in disordered one-dimensional solids gives rise
to an exponential suppression of transmission, which is known as Anderson
localization. Here, we experimentally study Anderson localization in a
superconducting waveguide quantum electrodynamics system comprising eight
individually tunable qubits coupled to a photonic continuum of a waveguide.
Employing the qubit frequency control, we artificially introduce frequency
disorder to the system and observe an exponential suppression of the
transmission coefficient in the vicinity of its subradiant dark modes. The
localization length decreases with the disorder strength, which we control
in-situ by varying individual qubit frequencies. Employing a one-dimensional
non-interacting model of coupled qubits and photons, we are able to support and
complement the experimental results. The difference between our investigation
and previous studies of localization in qubit arrays is the coupling via a
common waveguide, allowing us to explore the localization of mediating photons
in an intrinsically open system. The experiment opens the door to the study of
various localization phenomena on a new platform, which offers a high degree of
control and readout possibilities.
