Probing decoherence at an atom-defect quantum interface*

The atomic-scale quantum properties of interfaces play a central role in the ubiquitous surface-mediated decoherence that currently limits a wide variety of quantum technologies. We have constructed a novel instrument for quantitatively studying decoherence at active quantum surfaces. This hybrid quantum system combines neutral atoms adsorbed onto a diamond surface in ultrahigh vacuum conditions and subsurface nitrogen vacancy (NV) centers. We present measurements of the decoherence and relaxation rates of shallow NV centers interacting with atomic adsorbates deposited at thicknesses varying from angstroms to nanometers. As adsorbate atoms are added, we observe a significant reduction in spin relaxation time. We present progress towards a detailed understanding of coherence at this model quantum interface, with important consequences for a broad range of quantum interfaces.