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Kehayias, Pauli

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Kehayias

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Pauli

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Kehayias, Pauli

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2017 - 20182

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Author's Publications: search.filters.isAuthorOfPublication.f0246b07-bcd4-4dd2-8ca4-3155982c797d

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    Micrometer‐scale Magnetic Imaging of Geological Samples Using a Quantum Diamond Microscope
    (American Geophysical Union (AGU), 2017-08) Glenn, D. R.; Fung, Raymond; Kehayias, Pauli; Le Sage, David; Lima, E; Weiss, B; Walsworth, Ronald
    Remanent magnetization in geological samples may record the past intensity and direction of planetary magnetic fields. Traditionally, this magnetization is analyzed through measurements of the net magnetic moment of bulk millimeter to centimeter sized samples. However, geological samples are often mineralogically and texturally heterogeneous at submillimeter scales, with only a fraction of the ferromagnetic grains carrying the remanent magnetization of interest. Therefore, characterizing this magnetization in such cases requires a technique capable of imaging magnetic fields at fine spatial scales and with high sensitivity. To address this challenge, we developed a new instrument, based on nitrogen‐vacancy centers in diamond, which enables direct imaging of magnetic fields due to both remanent and induced magnetization, as well as optical imaging, of room‐temperature geological samples with spatial resolution approaching the optical diffraction limit. We describe the operating principles of this device, which we call the quantum diamond microscope (QDM), and report its optimized image‐area‐normalized magnetic field sensitivity (20 µT⋅µm/Hz1/2), spatial resolution (5 µm), and field of view (4 mm), as well as trade‐offs between these parameters. We also perform an absolute magnetic field calibration for the device in different modes of operation, including three‐axis (vector) and single‐axis (projective) magnetic field imaging. Finally, we use the QDM to obtain magnetic images of several terrestrial and meteoritic rock samples, demonstrating its ability to resolve spatially distinct populations of ferromagnetic carriers.
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    Ultralong Dephasing Times in Solid-State Spin Ensembles via Quantum Control
    (American Physical Society (APS), 2018-07-25) Bauch, Erik; Hart, Connor; Schloss, Jennifer; Turner, Matthew; Barry, John; Kehayias, Pauli; Singh, Swati; Walsworth, Ronald
    Quantum spin dephasing is caused by inhomogeneous coupling to the environment, with resulting limits to the measurement time and precision of spin-based sensors. The effects of spin dephasing can be especially pernicious for dense ensembles of electronic spins in the solid state, such as nitrogen-vacancy (NV) color centers in diamond. We report the use of two complementary techniques, spin-bath driving, and double quantum coherence magnetometry, to enhance the inhomogeneous spin dephasing time (T∗2) for NV ensembles by more than an order of magnitude. In combination, these quantum control techniques (i) eliminate the effects of the dominant NV spin ensemble dephasing mechanisms, including crystal strain gradients and dipolar interactions with paramagnetic bath spins, and (ii) increase the effective NV gyromagnetic ratio by a factor of two. Applied independently, spin-bath driving and double quantum coherence magnetometry elucidate the sources of spin ensemble dephasing over a wide range of NV and bath spin concentrations. These results demonstrate the longest reported T∗2 in a solid-state electronic spin ensemble at room temperature and outline a path towards NV-diamond dc magnetometers with broadband femtotesla sensitivity.