  We propose a method to probe and control the interactions between an ensemble
of magnetic impurities in a superconductor via microwave radiation. Our method
relies upon the presence of sub-gap Yu-Shiba-Rusinov (YSR) states associated
with the impurities. Depending on the sign of the detuning, radiation generates
either a ferro- or antiferromagnetic contribution to the exchange interaction.
This contribution can bias the statistics of the random exchange constants
stemming from the RKKY interaction. Moreover, by measuring the microwave
response at the YSR resonance, one gains information about the magnetic order
of the impurities. To this end, we estimate the absorption coefficient as well
as the achievable strength of the microwave-induced YSR-interactions using
off-resonant radiation. The ability to utilize microwave fields to both probe
and control impurity spins in a superconducting host may open new paths to
studying metallic spin glasses.
