arXiv subjects

Nikhita Khera

Publications and source records attributed to Nikhita Khera.

6 recordsLinked to original sources

arXiv2026

Methods for traceable scanning magnetometry using single nitrogen vacancy centers in diamond: determining orientation, distance and localization

Individual, scannable nitrogen vacancy (NV) centers in single crystal diamond nanostructures enable nanoscale, quantitative imaging of magnetic stray fields. Nevertheless, important parameters like distance between the NV center and the sample and the orientation of the NV high symmetry axis are often not known precisely and enter data evaluation as free fitting parameters. We here use scanning NV imaging on micro-patterned, perpendicularly magnetized stripes and discs. From these measurements, we directly infer NV - sample distance d_NV and the NV's azimuthal orientation without the need for an external vector magnet control. We determine d_NV = 31.5 nm, while we infer the azimuthal orientation with a precision of 3°. We additionally employ commercially available silicon needles to image the apex topography of our diamond nanostructures to detect surface contamination. Simultaneously, monitoring NV fluorescence as a function of the needle's position allows us to estimate the lateral placement of the NV inside the diamond nanostructure.

cond-mat.mes-hall↗

arXiv2026

Direct Laser Writing of Ferromagnetic Nickel Utilizing the Principle of Sensitized Triplet-Triplet Annihilation Upconversion

Direct laser writing of ferromagnetic microstructures is of great interest for sensing and data storage in compact three-dimensional architectures. However, reliable direct laser writing of metallic and even more so ferromagnetic materials remains a major challenge. Here, we present a novel photoresist suitable to direct laser write ferromagnetic nickel based on sensitized triplet-triplet annihilation upconversion. By combining an in-situ photochemical deoxygenation process with a sensitized triplet-triplet annihilation upconversion process as well as a photoreduction of Ni2+ ions, the deposition of metallic nickel is enabled under ambient conditions. Using this approach, nickel structures are fabricated as a proof of concept. Scanning electron microscopy and EDX analysis confirm the spatially confined deposition of nickel, while magnetic characterization by vibrating sample magnetometry and scanning NV magnetometry demonstrate the ferromagnetic nature of the printed structures. This work presents a major step forward in extending the possibilities of direct laser writing to metallic and ferromagnetic materials.

cond-mat.mtrl-sci↗

arXiv2026

FRET between NV centers in diamond and chlorophyll molecules: a novel resource for multimodal sensing and imaging in plant cells

This work demonstrates efficient Forster resonance energy transfer (FRET) between ensembles of shallow nitrogen-vacancy (NV) centers located 7 nm and 9 nm below a single-crystal diamond surface and a naturally occurring fluorophore, namely a mixture of chlorophyll a and b molecules extracted from Arabidopsis thaliana. The broad fluorescence band of NV centers spectrally overlaps with the absorption of chlorophyll molecules, enabling FRET. As a result, depositing a chlorophyll layer on the diamond surface reduces the NV fluorescence lifetime from approximately 14 ns to below 4 ns, indicating efficient energy transfer. Laser-induced photobleaching of chlorophyll restores the unquenched NV lifetime. In contrast, NV centers located deeper within the diamond at depths of 40 nm and 72 nm remain unaffected, confirming that the observed quenching originates from a short-range FRET mechanism. The NV ensembles retain their optically detected magnetic resonance contrast while FRET is observed, demonstrating preservation of their spin properties. These proof-of-principle experiments establish the feasibility of combining FRET-based distance measurements with magnetic sensing using optically readable spins.

physics.bio-ph↗

arXiv2025

Influence of Platinum Thin Films on the Photophysical and Quantum Properties of Near-Surface NV Centers

Nitrogen-vacancy (NV) centers in diamond are optically addressable spin defects with great potential for nanoscale quantum sensing. A key application of NV centers is the detection of external spins at the diamond surface. Among metals, platinum thin films - widely used in spintronics, catalysis and electrochemistry - provide a particularly interesting system for such studies. However, the interaction between NV centers and metals is known to affect their quantum sensing capabilities. In this work, we study five platinum-covered diamond samples containing shallow NVs created via nitrogen implantation with different energies (2.5-60 keV) and investigate the optical and quantum properties of NV ensembles beneath the metal films. We find a substantial reduction of the photoluminescence lifetime and a pronounced decrease of the NV$^{-}$ population for NV ensembles located near the platinum layer. As a result, optically detected magnetic resonance experiments could only be efficiently performed on diamonds implanted with at least 20 keV, where we observed a strong increase in the T$_{2}$ coherence time beneath the platinum thin films. Our study describes the various processes affecting NV centers near platinum films and provides guidance for the integration of thin metal films with near-surface NV centers.

cond-mat.mes-hall↗

arXiv2024

STRAW-b (STRings for Absorption length in Water-b): the second pathfinder mission for the Pacific Ocean Neutrino Experiment

Since 2018, the potential for a high-energy neutrino telescope, named the Pacific Ocean Neutrino Experiment (P-ONE), has been thoroughly examined by two pathfinder missions, STRAW and STRAW-b, short for short for Strings for Absorption Length in Water. The P-ONE project seeks to install a neutrino detector with a one cubic kilometer volume in the Cascadia Basin's deep marine surroundings, situated near the western shores of Vancouver Island, Canada. To assess the environmental conditions and feasibility of constructing a neutrino detector of that scale, the pathfinder missions, STRAW and STRAW-b, have been deployed at a depth of 2.7 km within the designated site for P-ONE and were connected to the NEPTUNE observatory, operated by Ocean Networks Canada (ONC). While STRAW focused on analyzing the optical properties of water in the Cascadia Basin, \ac{strawb} employed cameras and spectrometers to investigate the characteristics of bioluminescence in the deep-sea environment. This report introduces the STRAW-b concept, covering its scientific objectives and the instrumentation used. Furthermore, it discusses the design considerations implemented to guarantee a secure and dependable deployment process of STRAW-b. Additionally, it showcases the data collected by battery-powered loggers, which monitored the mechanical stress on the equipment throughout the deployment. The report also offers an overview of STRAW-b's operation, with a specific emphasis on the notable advancements achieved in the data acquisition (DAQ) system and its successful integration with the server infrastructure of ONC.

astro-ph.IM↗

arXiv2021

POCAM in the IceCube Upgrade

The IceCube Neutrino Observatory at the geographic South Pole instruments a gigaton of glacial Antarctic ice with over 5000 photosensors. The detector, by now running for over a decade, will be upgraded with seven new densely instrumented strings. The project focuses on the improvement of low-energy and oscillation physics sensitivities as well as re-calibration of the existing detector. Over the last few years we developed a Precision Optical Calibration Module (POCAM) providing self-monitored, isotropic, nanosecond, light pulses for optical calibration of large-volume detectors. Over 20 next-generation POCAMs will be calibrated and deployed in the IceCube Upgrade in order to reduce existing detector systematics. We report a general overview of the POCAM instrument, its performance and calibration procedures.

astro-ph.HE↗