Solid state spins have recently emerged as a promising new system for quantum information and nanoscale sensing applications. In particular, they can be positioned in close proximity to surfaces, enabling nanometer resolution magnetometry and coherent coupling to other quantum systems. I will present recent results demonstrating the use of individual electronic spins associated with Nitrogen Vacancy (NV) centers in diamond to probe the spectral, spatial, and temperature dependent properties of magnetic Johnson noise near conductors. Measurements of Johnson noise close to polycrystalline silver films over a range of distances (20-200 nm) and temperatures (10-300 K) are in good agreement with conventional theory. However, we find that Johnson noise is dramatically suppressed close to single-crystal silver films at low temperatures, indicative of a substantial deviation from Ohm’s law at length scales below the electron mean free path. Our results are in excellent agreement with a generalized model of Johnson noise that accounts for the ballistic motion of electrons in the metal. Potential applications to the nanoscale probing of more complex materials and condensed matter phenomena will be discussed.
Time permitting, I will also present experimental results showing that the coherent evolution of a single NV spin can be coupled to the motion of a nearby magnetized mechanical resonator. Specifically, we use coherent manipulation of the spin to sense the driven and Brownian motion of the resonator under ambient conditions. I will discuss potential future applications of this technique including the detection of the zero-point fluctuations of a mechanical resonator, the realization of strong spin-phonon coupling at a single quantum level, and the implementation of quantum spin transducers.