Samuel J. Whiteley

Deflection of a vibrissa leads to a gradient of strain across mechanoreceptors in a mystacial follicle

Rodents use their vibrissae to detect and discriminate tactile features during active exploration. The site of mechanical transduction in the vibrissa sensorimotor system is the follicle sinus complex and its associated vibrissa. We study the mechanics within the ring sinus (RS) of the follicle in an ex vivo preparation of the mouse mystacial pad. The sinus region has a relatively dense representation of Merkel mechanoreceptors and longitudinal lanceolate endings. Two-photon laser-scanning microscopy was used to visualize labeled cell nuclei in an ∼ 100-nl vol before and after passive deflection of a vibrissa, which results in localized displacements of the mechanoreceptor cells, primarily in the radial and polar directions about the vibrissa. These displacements are used to compute the strain field across the follicle in response to the deflection. We observe compression in the lower region of the RS, whereas dilation, with lower magnitude, occurs in the upper region, with volumetric strain ΔV/V ∼ 0.01 for a 10° deflection. The extrapolated strain for a 0.1° deflection, the minimum angle that is reported to initiate a spike by primary neurons, corresponds to the minimum strain that activates Piezo2 mechanoreceptor channels.

Resonant optical spectroscopy and coherent control of Cr4+ spin ensembles in SiC and GaN

The authors identify a new class of optically controllable, semiconductor-based defect spin that is formed from the

Optical charge state control of spin defects in 4H-SiC

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Electrometry by optical charge conversion of deep defects in 4H-SiC

-orbital electrons of chromium ions in silicon carbide and gallium nitride. These ions possess a simple lambda optical structure that couples only weakly to phonons and lattice strain. Therefore, even though they probe an ensemble of many ions at once with varying strain environments, the optical transitions they observe are exceptionally narrow and possess a high radiative efficiency. These properties allow the authors to individually interrogate the magnetic sublevels of the ground-state spin using resonant optical excitation, enabling ensemble optical spin polarization as well as optically detected magnetic resonance in the time domain. Each ion species emits the majority of its luminescence within a near-infrared zero-phonon line, suggesting a capacity for efficient photonic integration. Additionally, as magnetically active

Probing spin-phonon interactions in silicon carbide with Gaussian acoustics.

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Coherent Control of Spins with Gaussian Acoustics

-orbital states, the spins of these ions possess a number of degrees of design freedom not available to other common defect spin species such as those based on vacancy complexes. The authors therefore expect that these studies will broaden the range of opportunities available to semiconductor-based quantum device engineering, and will motivate further explorations into the use of transition metal ions as optically active qubit states.

Quantum control of surface acoustic wave phonons

Defects in silicon carbide (SiC) have emerged as a favorable platform for optically active spin-based quantum technologies. Spin qubits exist in specific charge states of these defects, where the ability to control these states can provide enhanced spin-dependent readout and long-term charge stability. We investigate this charge state control for two major spin qubits in 4H-SiC, the divacancy and silicon vacancy, obtaining bidirectional optical charge conversion between the bright and dark states of these defects. We measure increased photoluminescence from divacancy ensembles by up to three orders of magnitude using near-ultraviolet excitation, depending on the substrate, and without degrading the electron spin coherence time. This charge conversion remains stable for hours at cryogenic temperatures, allowing spatial and persistent patterning of the charge state populations. We develop a comprehensive model of the defects and optical processes involved, offering a strong basis to improve material design and to develop quantum applications in SiC.Defects in silicon carbide represent a viable candidate for realization of spin qubits. Here, the authors show stable bidirectional charge state conversion for the silicon vacancy and divacancy, improving the photoluminescence intensity by up to three orders of magnitude with no effect on spin coherence.

Imaging dynamically-driven strain at the nanometer-scale using stroboscopic Scanning X-ray Diffraction Microscopy.

Significance Electric field sensing is an important tool in metrology and characterization applications. Here we show that photoluminescent defects in silicon carbide, such as divacancies and silicon vacancies, can provide local information of radio-frequency electric fields. Using all-optical excitation, the charge state of the defect is controlled, measured, and shown to be affected by this electric field. This sensing technique enables spatial 3D mapping as well as spectral resolution of the electric field. By taking advantage of the piezoelectricity in silicon carbide, the technique also provides similar information on local radio-frequency strain waves. This method is expected to be broadly applicable to other materials and of interest for high-power electronics and high-frequency microelectromechanical systems. Optically active point defects in various host materials, such as diamond and silicon carbide (SiC), have shown significant promise as local sensors of magnetic fields, electric fields, strain, and temperature. Modern sensing techniques take advantage of the relaxation and coherence times of the spin state within these defects. Here we show that the defect charge state can also be used to sense the environment, in particular high-frequency (megahertz to gigahertz) electric fields, complementing established spin-based techniques. This is enabled by optical charge conversion of the defects between their photoluminescent and dark charge states, with conversion rate dependent on the electric field (energy density). The technique provides an all-optical high-frequency electrometer which is tested in 4H-SiC for both ensembles of divacancies and silicon vacancies, from cryogenic to room temperature, and with a measured sensitivity of 41±8 (V/cm)2/Hz. Finally, due to the piezoelectric character of SiC, we obtain spatial 3D maps of surface acoustic wave modes in a mechanical resonator.