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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.