Controlled Encapsulation of Nanodiamond Qubits by Metal-Organic Frameworks: Towards Enhanced Quantum Sensing

S. Crawford, R. Shugayev, G. Lander, H. Paudel, Y. Duan, J. Baltrus, N. Diemler, J. Ellis, K. Kim, P. Cvetic
National Energy Technology Laboratory/Leidos, Inc.,
United States

Keywords: nanodiamonds, quantum sensing, quantum materials, metal-organic framework, qubits


The field of quantum sensing is rapidly maturing, with an increasing number of commercial entrants, strategic government investments, and new innovations in quantum networking, sensing, and computing. Although this maturation will have important implications for a range of economic sectors, such as defense, finance, and industry, there are particularly intriguing opportunities for energy applications. Quantum sensing technologies will significantly aid oil and gas discovery, critical mineral detection, and pipeline integrity monitoring. A key challenge is the development of advanced qubit materials capable of highly selective analyte uptake and detection that can operate under environmentally relevant conditions. Nanodiamonds (NDs) containing nitrogen vacancy (NV) centers are an intriguing material for quantum information science applications, and quantum sensing in particular, as NV ND qubits are commercially available and can be operated at room temperature. The performance of NDs in quantum sensing applications can be significantly influenced by their surface coating. Here, we demonstrate the controlled encapsulation of NDs by the metal-organic framework (MOF) ZIF-8. MOFs are highly ordered, crystalline, porous materials with structural and chemical properties that can be tuned through the use of different metal centers and organic linkers, providing nearly unlimited possibilities for rational material design. Embedding qubits in porous crystalline materials such as MOFs creates new opportunities for enhanced quantum sensing, as the physical and chemical properties of the MOF pores can be controlled to selectively uptake specific target analytes such as ions or gasses to interact with encapsulated NDs. The ND@ZIF-8 composites were thoroughly characterized by multiple physical and optical methods. Environmental transmission electron microscopy videos demonstrate that the NDs are well-dispersed within the ZIF-8 matrix, and the NDs@ZIF-8 composites were further characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, confirming the ZIF-8 structure. The concentration of NDs in individual ZIF-8 crystals could be tuned by simply controlling the concentration of NDs added during the composite material synthesis. Crucially, the photoluminescent properties of the NDs are preserved following ZIF-8 encapsulation. Moreover, the NDs@ZIF-8 exhibited characteristic optically detected magnetic resonance (ODMR) spectra, an important quantum sensing experiment for detecting multiple targets, including electromagnetic fields, temperature, and pressure. Furthermore, ZIF-8 functionalization lengthens the spin longitudinal relaxation time T1 of the NDs by up to a factor of 4, which is a critical figure of merit for spin relaxometry-based quantum sensing to detect analytes such as metal ions. Taken together, this work provides a foundation for further development of ND@MOF composites, which has important implications for quantum sensing, quantum computing, and related applications.