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Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit

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Science  06 Mar 2015:
Vol. 347, Issue 6226, pp. 1129-1132
DOI: 10.1126/science.aaa4298
  • Fig. 1 Probing Johnson noise with single-spin qubits.

    (A) The thermally induced motion of electrons in silver generates fluctuating magnetic fields (Embedded Image), which are detected with the spin of a single NV. The NV is polarized and read out through the back side of the diamond. (B) The NV spin is polarized into the Embedded Imagestate using a green laser pulse. Spin relaxation into the Embedded Image states is induced by magnetic field noise at ∼2.88 GHz. After wait time τ, the population left in Embedded Image is read out by spin-dependent fluorescence. All measurements shown were performed at low magnetic fields (Embedded Image). (C) Spin relaxation data for the same single shallow-implant NV before silver deposition (open blue squares), with silver deposited (red circles) and after the silver has been removed (open blue triangles). (D) Spin relaxation for a single NV close to a silver film prepared in the Embedded Image state (red circles) and in the Embedded Image state (open orange circles). (Inset) Spin relaxation for a single native NV in bulk diamond in the Embedded Image state (blue circles) and in the Embedded Image state (open light blue circles).

  • Fig. 2 Distance dependence of NV relaxation close to silver.

    (A) A gradual SiO2 ramp (slope of ∼0.2 nm/μm) is grown on the diamond surface, followed by a 60-nm silver film. (B) The NV relaxation rate is measured as a function of position along the ramp, which is then converted to distance to the film. At each point, 5 to 10 NV centers are measured, and the minimum rate measured is plotted (red circles). The horizontal error bars reflect 1 SD in the estimated distance to the film including the uncertainty in NV depth, while the vertical error bars reflect 1 SD in the fitted relaxation rate. The red dashed line shows the expected relaxation rate with no free parameters after accounting for the finite silver film thickness. (Inset) Thickness of the ramp as a function of lateral position along the diamond sample (blue curve). The red crosses correspond to the positions along the sample where the measurements were taken.

  • Fig. 3 Temperature dependence of NV relaxation close to polycrystalline silver.

    (A) The measured relaxation rate of a single NV spin under a polycrystalline silver film as a function of temperature (red data points). The error bars reflect 1 SD in the fitted relaxation rate. The conductivity of the silver film as a function of temperature shown in (B) is included in a fit to Eq. 2, with the distance to the film as the single free parameter (red dashed line). The extracted distance is Embedded Image nm. (B) The conductivity of the 100-nm-thick polycrystalline silver film deposited on the diamond surface is measured as a function of temperature. (Inset) Grain boundaries within the polycrystalline silver film, imaged using electron backscatter diffraction. The average grain diameter is 140 nm, with a SD of 80 nm.

  • Fig. 4 Temperature dependence of NV relaxation close to single-crystal silver.

    (A) Measured conductivity of single-crystal (blue curve) and polycrystalline (red curve, same as Fig. 3B) silver as a function of temperature. (Inset) Electron backscatter diffraction image of the single-crystal silver film showing no grain boundaries, and the observed diffraction pattern. (B) Relaxation of a single NV spin under single-crystal silver as a function of temperature (blue squares). The error bars reflect 1 SD in the fitted relaxation rate. Equation 2 is fit to the data from 200 to 295 K (blue dashed line). A nonlocal model (23) is fit to the data (blue solid line); the extracted distance between the NV and the silver surface is Embedded Image nm. (C) Cartoon illustrating the relevant limits, where the noise is dominated by diffusive electron motion (left, Embedded Image) and ballistic motion (right, Embedded Image). (D) The same data as in (B) were taken for 23 NVs at varying distances from the film. The Embedded Image of each NV at 103 K (top) and 27 K (bottom) is plotted against the extracted depth (blue triangles). The horizontal error bars reflect 1 SD in the fitted distance to the film, while the vertical error bars reflect 1 SD in the fitted relaxation time. The nonlocal model (solid colored lines) saturates at a finite lifetime determined by Eq. 3 (bottom, dashed black line), whereas the local model does not (dashed colored lines).

Supplementary Materials

  • Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit

    S. Kolkowitz, A. Safira, A. A. High, R. C. Devlin, S. Choi, Q. P. Unterreithmeier, D. Patterson, A. S. Zibrov, V. E. Manucharyan, H. Park, M. D. Lukin

    Materials/Methods, Supplementary Text, Tables, Figures, and/or References

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    • Materials and Methods
    • Figs. S1 to S7
    • Tables S1 to S3
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