April 23, 2015 – Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit

Kolkowitz et al. of Harvard University used nitrogen-vacancy centers in diamond to make single-spin qubits for measuring Johnson noise thermally induced in a conductive silver film in the vicinity indicating that nanoscale quantum systems may be controlled by nearby electrodes. Read the original article: Thermally induced electrical currents, known as Johnson noise, cause fluctuating electric and magnetic fields in proximity to a conductor. These fluctuations are intrinsically related to the conductivity of the metal. We use single-spin qubits associated with nitrogen-vacancy centers in diamond to probe Johnson noise in the vicinity of conductive silver films. Measurements of polycrystalline silver films over a range of distances (20 to 200 nanometers) and temperatures (10 to 300 kelvin) are consistent with the classically expected behavior of the magnetic fluctuations. However, we find that Johnson noise is markedly suppressed next to single-crystal films, indicative of a substantial deviation from Ohm’s law at length scales below the electron mean free path. Our results are consistent with a generalized model that accounts for the ballistic motion of electrons in the metal, indicating that under the appropriate conditions, nearby electrodes may be used for controlling nanoscale optoelectronic, atomic, and solid-state quantum systems. Science 6 March 2015: Vol. 347 no. 6226 pp. 1129-1132, DOI: 10.1126/science.aaa4298  (Posted by Y. Tzeng)

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