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Nanoscale imaging magnetometry with diamond spins under ambient conditions Balasubramanian, G., et al. Nature 455, 648

Nanoscale imaging magnetometry with diamond spins under ambient conditions Balasubramanian, G., et al. Nature 455, 648-651 (2008). John Watson 4/15/2009. Outline. Introduction and background Balasubramanian paper Proposed improvements Maze paper Proposed improvements Conclusion.

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Nanoscale imaging magnetometry with diamond spins under ambient conditions Balasubramanian, G., et al. Nature 455, 648

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  1. Nanoscale imaging magnetometry with diamond spins under ambient conditionsBalasubramanian, G., et al. Nature 455, 648-651 (2008). John Watson 4/15/2009

  2. Outline • Introduction and background • Balasubramanian paper • Proposed improvements • Maze paper • Proposed improvements • Conclusion

  3. Introduction: Why do we care? • Degen, C., Nature Nanotechnology 3, 643-644 (2008).

  4. Introduction: Why do we care? • Room temperature measurements • Biological applications • Single spin detection (electron and neutron) • Quantum experiments – mechanical transport of qubit? • Markers in bio applications

  5. The system • Vacancy produced by electron radiation • Number of vacancies measurable with fluorescence autocorrelation Taylor, J.M., et al., Nature Physics 4, 810-816 (2008).

  6. Method • Optically pump into ms=0 • Split ms=±1 with external B field • Microwave induced dipole transitions • Observe modulation of scattering fluorescence with confocal microscope Right: optically detected magnetic resonance spectra for single nitrogen vacancy

  7. Confocal microscope

  8. Experiment 1: map probe tip • Look at ESR spectra to determine |B| • Simultaneous AFM to locate vacancy

  9. Resolution • Lock microscope and AFM together • Fixed microwave B • Modulate fluorescence with probe tip • Note sub-wavelength resolution • Dark ring gives maximum resolution – 5 nm

  10. Experiment 2: Vector magnetometer • Excite with microwave field • Scan surface

  11. Results • Shadow due to polarization destruction • 5 mT line represents vacancy resonance • 20 nm line x 25 uT/nm gradient = .5 mT resolution

  12. Proposed improvements • Phase lock with AFM oscillation • Spin echo technique (i.e. ac B field) • Get narrower ESR linewidth • Predicted improvements: 3 uT and sub-nm spatial resolution • Possibly image nuclear spins at 5nm, room temperature

  13. Nanoscale magnetic sensing with an individual electronic spin in diamond. Maze, et al. Nature, 455, 644-647 (2008) • Bulk diamond with vacancy near surface or nanocrystal on substrate • Split degeneracy with DC B field (Helmholtz pair), manipulate with microwave B, spin echo with AC B field, observe ESR spectra with confocal microscopy

  14. Methods

  15. Spin echo technique <n> = .03 photons/324 ns • Problem: C13 spins limit coherence time • Solution: apply DC B field to tune frequency to AC field to measure • Measure fluorescence at peaks Nitrogen vacancy spin-echo signal Fluorescence signal

  16. Methods 3.15 kHz • Signal oscillation due to nitrogen spin accumulating phase from AC field • Phase corresponds to spin population difference • Leads to fluorescence variation 4.21 kHz Measured spin echo signal for two operating frequencies. Maximum slope corresponds to maximum sensitivity.

  17. Sensitivity • Expect sensitivity to scale as • Sensitivity optimized for frequencies comparable with spin echo coherence • Photon collection efficiency of .1% limits current sensitivity

  18. Results • Ultrapure bulk sample: 3 nT at kilohertz frequencies with 100 second averaging (roughly 30 nT/Hz-1/2) • Nanocrystal (34 ± 12 nm size): .5 ± .1 μT Hz-1/2 • Stuttgart group (40 nm, single vacancy crystal): .5 mT

  19. Future work • Get samples with fewer 13C isotopes • Improve photon collection with far-field optics or evanescent near-field coupling to waveguides

  20. Conclusion • Proof of principle demonstrated • Much smaller volume than current technology • Can detect ~ 7 electron spins • Significant improvement needed to resolve nuclear spins

  21. References • Nanoscale imaging magnetometry with diamond spins under ambient conditions. Balasubramanian, G., et al. Nature 455, 648-651 (2008). • Nanoscale Magnetometry – Microscopy with Single Spins. Degen, C., Nature Nanotechnology 3, 643-644 (2008). • High-sensitivity diamond magnetometer with nanoscale resolution. Taylor, J.M., et al., Nature Physics 4, 810-816 (2008). • Nanoscale magnetic sensing with an individual electronic spin in diamond. Maze, et al. Nature, 455, 644-647 (2008)

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