arXiv subjects

Vinaya K. Kavatamane

Publications and source records attributed to Vinaya K. Kavatamane.

6 recordsLinked to original sources

arXiv2026

Nanophotonic quantum magnetometry in a spin-dense diamond cavity

Quantum sensors based on the nitrogen-vacancy (NV) center in diamond are leading platforms for high-sensitivity magnetometry with nanometer-scale resolution. State-of-the-art implementations, however, typically rely on bulky free-space optics or sacrifice spatial resolution to achieve high sensitivities. Here, we realize an integrated platform that overcomes this trade-off by fabricating monolithic whispering-gallery-mode cavities from a diamond chip containing a high density of NV centers and by evanescently coupling excitation to and photoluminescence from the cavity using a tapered optical fiber. Employing a lock-in-amplified Ramsey magnetometry scheme, we achieve a photon-shot-noise-limited DC sensitivity of $58\,\text{nT}/\sqrt{\text{Hz}}$---the best sensitivity reported to date for a nanofabricated cavity-based magnetometer. The microscopic cavity size enables micrometer-scale spatial resolution and low-power operation, while fiber-coupling provides a path to scalable on-chip integration. Arrays of such sensors could enable NV-NMR spectroscopy of sub-nanoliter samples, new magnetic-gradient imaging architectures, and compact biosensing platforms.

physics.optics↗

arXiv2026

Single-Spin Nitrogen-Vacancy Hybrid Magnetometer with Enhanced Static Field Sensitivity

Precision sensing and imaging of weak static magnetic fields are crucial for a variety of emerging nanoscale applications. While nitrogen-vacancy (NV) centers in diamond provide exceptional AC magnetic field sensitivity with nanoscale spatial resolution, their sensitivity to static (DC) magnetic fields is fundamentally limited by the short dephasing time (T2*) due to spin-spin interactions. In this work, we present a novel hybrid sensing approach that integrates a soft ferromagnetic microwire with a single near-surface NV center to amplify its response to external static magnetic fields. This hybrid configuration achieves a DC magnetic field sensitivity of 63 nT/sqrt(Hz) for a single NV center - about 500 times greater than conventional inhomogeneous broadening- or T2*-limited magnetometry, with potential for further enhancement. The compact and highly sensitive nature of this sensor opens new opportunities for quantum sensing applications involving the detection of static or slowly varying magnetic fields across diverse scientific and technological domains.

quant-ph↗

arXiv2026

Nonlinear optical charge state switching and pumping to a diamond NV center dark state

The photodynamics of diamond nitrogen-vacancy (NV) centers limits their performance in many quantum technologies. Quenching of photoluminescence, which degrades NV readout, is commonly ascribed to a dark state that is not fully understood. Using a nanoscale cavity to generate intense infrared fields that quench NV emission nonlinearly with field intensity, we show that the dark state is accessed by two-photon pumping into the $^4\!A_2$ quartet state of the neutrally charged NV (NV$^0$). We constrain this state's energy relative to the NV$^0$ ground-state ($^2\!E$) to ${<}0.58$\,eV and the recombination energy threshold to the NV$^-$ ground state ($^3\!A_2$) to $\leq2.33\,\text{eV}$. Furthermore, we estimate the intrinsic lifetime of $^4\!A_2$ state to be $1.78-6.06\,μ\text{s}$ and show that accessing this state allows sensing of local infrared fields. This new understanding will allow predictions of the limits of NV technologies reliant upon intense fields, including levitated systems, spin--optomechanical devices, and absorption--based magnetometers.

quant-ph↗

arXiv2026

Optical Switching of $χ^{(2)}$ in Diamond Photonics

Diamond's unique physical properties make it a versatile material for a wide range of nonlinear and quantum photonic technologies. However, unlocking diamond's full potential as a nonlinear photonic material with non-zero second-order susceptibility $χ^{(2)}\neq0$ requires symmetry breaking. In this work, we use a nanoscale cavity to demonstrate second-harmonic generation (SHG) in diamond, and demonstrate, for the first time, that the magnitude of the diamond's effective $χ^{(2)}$ strongly depends on the electronic configuration of defects in the diamond crystal, such as nitrogen-vacancy centres. The modification of $χ^{(2)}$ arises from photoionisation from the negative to neutral charge-state, and is manifested by quenching of SHG upon green illumination. Toggling the green illumination allows for optical switching of the device's $χ^{(2)}$. Optical control of $χ^{(2)}$ by defect engineering opens the door for second-order nonlinear processes in diamond.

physics.optics↗

arXiv2025

Reversing Annealing-Induced Optical Loss in Diamond Microcavities

A key challenge for quantum photonic technologies based on spin qubits is the creation of optically active defects in photonic resonators. Several of the most promising defects for quantum applications are hosted in diamond, and are commonly created through ion implantation and annealing at high temperatures and high vacuum. However, the impact of annealing on photonic resonator quality factor, a critical parameter governing their coupling to defects, has not been reported. In this work, we characterize the effect of annealing at temperatures >1200°C in high vacuum on the quality factors of diamond microdisk resonators. We investigate the optical losses associated with a non-diamond layer formed during annealing, and use Raman spectroscopy to analyze the resonator surface morphology and demonstrate that tri-acid cleaning can restore their optical quality factors. These results show the viability of creating defects in pre-fabricated diamond resonators without degrading their optical properties.

physics.optics↗

arXiv2022

Diamond Integrated Quantum Photonics: A Review

Integrated quantum photonics devices in diamond have tremendous potential for many quantum applications, including long-distance quantum communication, quantum information processing, and quantum sensing. These devices benefit from diamond's combination of exceptional thermal, optical, and mechanical properties. Its wide electronic bandgap makes diamond an ideal host for a variety of optical active spin qubits that are key building blocks for quantum technologies. In landmark experiments, diamond spin qubits have enabled demonstrations of remote entanglement, memory-enhanced quantum communication, and multi-qubit spin registers with fault-tolerant quantum error correction, leading to the realization of multinode quantum networks. These advancements put diamond at the forefront of solid-state material platforms for quantum information processing. Recent developments in diamond nanofabrication techniques provide a promising route to further scaling of these landmark experiments towards real-life quantum technologies. In this paper, we focus on the recent progress in creating integrated diamond quantum photonic devices, with particular emphasis on spin-photon interfaces, cavity optomechanical devices, and spin-phonon transduction. Finally, we discuss prospects and remaining challenges for the use of diamond in scalable quantum technologies.

quant-ph↗