Nanodiamond-Based Optical-Fiber Quantum Probe for Magnetic Field and Biological Sensing

Fluorescence dynamics of color centers in diamond needles

This study presents a detailed investigation into the fluorescence properties of color centers in single-crystal diamond needles (SCDNs) synthesized via chemical vapor deposition. Using steady-state and time-resolved photoluminescence (PL) techniques, we identified color centers with zero-phonon lines at 389 nm, 468 nm, 575 nm (NV0), 637 nm (NV-), and 738 nm (SiV-). PL excitation spectroscopy conducted at room temperature revealed the complex electronic structure of some of these centers, paving the way for further investigation into their fluorescence properties. Lifetime measurements were performed for each center, with the 389 nm one exhibiting the longest decay time (∼30 ns), which is advantageous for enhancing quantum coherence, improving photon emission efficiency, and reducing power consumption. Altogether, these findings highlight the potential of SCDNs for quantum applications and confirm their promise as a platform for next-generation photonic and quantum devices.

Fiber‐Integrated van der Waals Quantum Sensor with an Optimal Cavity Interface

Integrating quantum materials with fiber optics adds advanced functionalities to a variety of applications, and introduces fiber‐based quantum devices such as remote sensors capable of probing multiple physical parameters. However, achieving optimal integration between quantum materials and fibers is challenging, particularly due to difficulties in fabrication of quantum elements with suitable dimensions and an efficient photonic interface to a commercial optical fiber. Here a new modality for a fiber‐integrated van der Waals quantum sensor is demonstrated. A hole‐based circular Bragg grating cavity from hexagonal boron nitride (hBN) is designed and fabricated, engineer optically active spin defects within the cavity, and integrate the cavity with an optical fiber using a deterministic pattern transfer technique. The fiber‐integrated hBN cavity enables efficient excitation and collection of optical signals from spin defects in hBN, thereby enabling all‐fiber integrated quantum sensors. Moreover, remote sensing of a ferromagnetic material and of arbitrary magnetic fields is demonstrated. All in all, the hybrid fiber‐based quantum sensing platform may pave the way to a new generation of robust, remote, multi‐functional quantum sensors.

Exploring nanodiamonds: leveraging their dual capacities for anticancer photothermal therapy and temperature sensing

Cancer has become a primary global health concern, which has prompted increased attention towards targeted therapeutic approaches like photothermal therapy (PTT). The unique optical and magnetic properties of nanodiamonds (NDs) have made them versatile nanomaterials with promising applications in biomedicine. This comprehensive review focuses on the potential of NDs as a multifaceted platform for anticancer therapy, mainly focusing on their dual functionality in PTT and temperature sensing. The review highlighted NDs' ability to enhance PTT through hybridization or modification, underscoring their adaptability in delivering small molecule reagents effectively. Furthermore, NDs, particularly fluorescent nanodiamonds (FNDs) with negatively charged nitrogen-vacancy centers, enable precise temperature monitoring, enhancing PTT efficacy in anticancer treatment. Integrating FNDs into PTT holds promise for advancing therapeutic efficacy by providing valuable insights into localized temperature variations and cell death mechanisms. This review highlights new insights into cancer treatment strategies, showcasing the potential of NDs to revolutionize targeted therapeutics and improve patient outcomes.

Sensing at the Nanoscale Using Nitrogen-Vacancy Centers in Diamond: A Model for a Quantum Pressure Sensor

The sensing of stress under harsh environmental conditions with high resolution has critical importance for a range of applications including earth's subsurface scanning, geological CO2 storage monitoring, and mineral and resource recovery. Using a first-principles density functional theory (DFT) approach combined with the theoretical modelling of the low-energy Hamiltonian, here, we investigate a novel approach to detect unprecedented levels of pressure by taking advantage of the solid-state electronic spin of nitrogen-vacancy (NV) centers in diamond. We computationally explore the effect of strain on the defect band edges and band gaps by varying the lattice parameters of a diamond supercell hosting a single NV center. A low-energy Hamiltonian is developed that includes the effect of stress on the energy level of a ±1 spin manifold at the ground state. By quantifying the energy level shift and split, we predict pressure sensing of up to 0.3 MPa/Hz using the experimentally measured spin dephasing time. We show the superiority of the quantum sensing approach over traditional optical sensing techniques by discussing our results from DFT and theoretical modelling for the frequency shift per unit pressure. Importantly, we propose a quantum manometer that could be useful to measure earth's subsurface vibrations as well as for pressure detection and monitoring in high-temperature superconductivity studies and in material sciences. Our results open avenues for the development of a sensing technology with high sensitivity and resolution under extreme pressure limits that potentially has a wider applicability than the existing pressure sensing technologies.