  We discuss how grand unification can be probed with experiments at low
energies using quantum sensors. Specifically, we show that scalar multiplets
coupled to the gauge sector of a grand unified theory provide a mechanism for a
time-varying unified coupling which has low-energy consequences which can be
probed with quantum sensors. We then assume that the multiplets represent ultra
light dark matter. Constraints on ultra light dark matter couplings to regular
matter are extracted using atomic clock comparisons, pulsar timing arrays
(NANOGrav) and MICROSCOPE.
