Single spin detection by magnetic resonance force microscopy

Abstract

Magnetic resonance imaging (MRI) is well known as a powerful technique for visualizing subsurface structures with three-dimensional spatial resolution. Pushing the resolution below 1?µm remains a major challenge, however, owing to the sensitivity limitations of conventional inductive detection techniques. Currently, the smallest volume elements in an image must contain at least 1012 nuclear spins for MRI-based microscopy1, or 107 electron spins for electron spin resonance microscopy2. Magnetic resonance force microscopy (MRFM) was proposed as a means to improve detection sensitivity to the single-spin level, and thus enable three-dimensional imaging of macromolecules (for example, proteins) with atomic resolution3,4. MRFM has also been proposed as a qubit readout device for spin-based quantum computers5,6. Here we report the detection of an individual electron spin by MRFM. A spatial resolution of 25?nm in one dimension was obtained for an unpaired spin in silicon dioxide. The measured signal is consistent with a model in which the spin is aligned parallel or anti-parallel to the effective field, with a rotating-frame relaxation time of 760?ms. The long relaxation time suggests that the state of an individual spin can be monitored for extended periods of time, even while subjected to a complex set of manipulations that are part of the MRFM measurement protocol.

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Figure 1: Configuration of the single-spin MRFM experiment.
Figure 2: Timing diagram for the iOSCAR spin manipulation protocol.
Figure 3: Plots showing the spin signal as the sample was scanned laterally in the x direction for two values of external field: a, Bext = 34?mT, and b, Bext = 30?mT.
Figure 4: By measuring the spin signal energy as a function of detection bandwidth, the power spectral density of the spin signal amplitude Δf1(t) can be determined.

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Acknowledgements

We thank J. Sidles, A. Hero, M. Ting, G. Berman, I. Martin, C. S. Yannoni and T. Kenny for discussions, and D. Pearson, Y. Hishinuma, M. Sherwood and C. Rettner for technical assistance. This work was supported by the DARPA Three-Dimensional Atomic-Scale Imaging programme administered through the US Army Research Office.

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Correspondence to D. Rugar.

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Supplementary information

Supplementary Video

This animated movie illustrates the cantilever-driven spin inversions that occur during the iOSCAR spin manipulation protocol (see Fig. 2 in the paper). The “Lock” and “Anti-lock” states correspond to the spin being either aligned or anti-aligned with respect to the effective field in the rotating frame, resulting in either positive or negative cantilever frequency shifts, respectively. Each time the microwave field is interrupted, the spin switches between the locked and anti-locked states and the phase of the spin inversions with respect to the cantilever motion is reversed. (MP4 933 kb)

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Rugar, D., Budakian, R., Mamin, H. et al. Single spin detection by magnetic resonance force microscopy. Nature 430, 329–332 (2004). https://doi.org/10.1038/nature02658

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