Dynamical sensitivity control of a single-spin quantum sensor.

The Nitrogen-Vacancy (NV) defect in diamond is a unique quantum system that offers precision sensing of nanoscale physical quantities at room temperature beyond the current state-of-the-art. The benchmark parameters for nanoscale magnetometry applications are sensitivity, spectral resolution, and dynamic range. Under realistic conditions the NV sensors controlled by conventional sensing schemes suffer from limitations of these parameters. Here we experimentally show a new method called dynamical sensitivity control (DYSCO) that boost the benchmark parameters and thus extends the practical applicability of the NV spin for nanoscale sensing. In contrast to conventional dynamical decoupling schemes, where π pulse trains toggle the spin precession abruptly, the DYSCO method allows for a smooth, analog modulation of the quantum probe's sensitivity. Our method decouples frequency selectivity and spectral resolution unconstrained over the bandwidth (1.85 MHz-392 Hz in our experiments). Using DYSCO we demonstrate high-accuracy NV magnetometry without |2π| ambiguities, an enhancement of the dynamic range by a factor of 4 · 103, and interrogation times exceeding 2 ms in off-the-shelf diamond. In a broader perspective the DYSCO method provides a handle on the inherent dynamics of quantum systems offering decisive advantages for NV centre based applications notably in quantum information and single molecule NMR/MRI

Laser-induced heating in a high-density ensemble of nitrogen-vacancy centers in diamond and its effects on quantum sensing.

Among quantum sensors, the single nitrogen-vacancy (NV) defect in diamond has the highest sensitivity-to-size factor. For instance, a single-NV spin when used as a magnetometer could achieve sensitivities of the order of nT/root Hz, while the dimensions of the sensor are merely atomic in size. The sensitivity is limited only by the photon shot noise. One method to boost the magnetometer sensitivity to pico-tesla scales is to use many NV defect centers as an ensemble sensor [Phys. Rev. X 5, 041001 (2015)]. However, during the absorption-emission (fluorescence) optical cycles, the NV centers transfer a portion of the irradiation laser energy into phonons and heat the diamond matrix. This results in unintended fluorescence decrease, spin resonance lines shifts, and fluctuations. Hence, the advantages gained by packing a high density of NV centers are significantly reduced. Here we investigate the heat generation of ensemble NV centers in micrometer-sized diamond under 532 nm laser irradiation and its effects pertaining to sensing applications. These investigations help us to find strategies that mitigate the detrimental effects of heating and yet permits the use of ensemble NV defects for improved metrology applications

Evaluation of the sealing ability of mineral trioxide aggregate repair HP, biodentine and white mineral trioxide aggregate as furcation repair materials: An in-vitro ultraviolet-spectrophotometric analysis

This study aims to evaluate the sealing ability of Mineral Trioxide Aggregate Repair HP, Biodentine and White Mineral Trioxide Aggregate(WMTA) as furcation repair materials by using Ultraviolet- Spectrophotometric analysis. A total of 80 freshly extracted human permanent mandibular first and second molar teeth were included. Teeth were decoronated 3mm above the cemento-enamel junction and roots were amputated 3mm below the furcation.  Endodontic access cavity opening was done and root canal orifices were sealed with sticky wax. Artificial perforations were made in furcation areas of teeth using round bur.80 specimens were divided into 3 Experimental groups with 20 specimens per group; Group A (MTA Repair HP), Group B (Biodentine), Group C (WMTA) used as furcation repair materials and the remaining 20 specimens were equally divided between Positive control and Negative control groups. Specimens were immersed in Indian ink dye for 48hours and were then subjected to dye extraction method by completely dissolving the teeth in 65% nitric acid and the obtained solutions were analysed using Ultraviolet-Spectrophotometer and readings were recorded as absorbance units. Obtained data was statistically analysed using One-way ANOVA and Tukey’s-Post hoc tests.&nbsp

Enhancing fluorescence excitation and collection from the nitrogen-vacancy center in diamond through a micro-concave mirror.

We experimentally demonstrate a simple and robust optical fiber based method to achieve simultaneously efficient excitation and fluorescence collection from Nitrogen-Vacancy (NV) defects containing micro-crystalline diamond. We fabricate a suitable micro-concave mirror that focuses scattered excitation laser light into the diamond located at the focal point of the mirror. At the same instance, the mirror also couples the fluorescence light exiting out of the diamond crystal in the opposite direction of the optical fiber back into the optical fiber within its light acceptance cone. This part of fluorescence would have been otherwise lost from reaching the detector. Our proof-of-principle demonstration achieves a 25 times improvement in fluorescence collection compared to the case of not using any mirrors. The increase in light collection favors getting high signal-to-noise ratio optically detected magnetic resonance signals and hence offers a practical advantage in fiber-based NV quantum sensors. Additionally, we compacted the NV sensor system by replacing some bulky optical elements in the optical path with a I x 2 fiber optical coupler in our optical system. This reduces the complexity of the system and provides portability and robustness needed for applications like magnetic endoscopy and remote-magnetic sensing. Published by AIP Publishing

An interlinked computational-experimental investigation into SnS nano-flakes for field emission application

Layered binary semiconductor materials have attracted significant interest as field emitters due to their low work function, mechanical stability, high thermal and electrical conductivity. Herein, we report a systematic experimental and theoretical investigation of SnS nanoflakes synthesized using a simple, low-cost, and non-toxic hot injection method for field emission studies. The field emission studies were carried out on SnS nanoflakes thin film prepared using a simple spin coat technique. The x-ray diffraction (XRD) and Raman spectroscopy analysis revealed an orthorhombic phase of SnS. Scanning electron microscopy (SEM) analysis revealed that as-synthesized SnS has flakes-like morphology. The formation of pure-phase SnS nanoflakes was further confirmed by x-ray photoelectron spectroscopy (XPS) analysis. The UV-Visible-NIR spectroscopy analysis shows that SnS nanoflakes have a sharp absorption edge observed in the UV region and have a band gap of ∼ 1.66 eV. In addition, the first-principles density functional theory (DFT) calculations were carried out to provide atomic-level insights into the crystal structure, band structure, and density of states (DOS) of SnS nanoflakes. The field emission properties of SnS nanoflakes were also investigated and found that SnS nanoflakes have a low turn-on field (∼ 6.2 V/μm for 10 μA/cm2), high emission current density (∼ 104 μA/cm2 at 8.0 V/μm), superior current stability (∼ 2.5 hrs for ∼ 1 μA) and a high field enhancement factor of 1735. The first principle calculations the predicted lower work function of different surfaces, especially for the most stable SnS (001) surface ( = 4.32 eV), is believed to be responsible for the observed facile electron emission characteristics. We anticipate that the SnS could be utilized for future vacuum nano/microelectronic and flat panel display applications due to the low turn-on field and flakes-like structure