Quantum sensing with optically accessible spin defects in van der Waals layered materials

Abstract

Quantum sensing has emerged as a powerful technique to detect and measure physical and chemical parameters with exceptional precision. One of the methods is to use optically active spin defects within solid-state materials. These defects act as sensors and have made significant progress in recent years, particularly in the realm of two-dimensional (2D) spin defects. In this article, we focus on the latest trends in quantum sensing that use spin defects in van der Waals (vdW) materials. We discuss the benefits of combining optically addressable spin defects with 2D vdW materials while highlighting the challenges and opportunities to use these defects. To make quantum sensing practical and applicable, the article identifies some areas worth further exploration. These include identifying spin defects with properties suitable for quantum sensing, generating quantum defects on demand with control of their spatial localization, understanding the impact of layer thickness and interface on quantum sensing, and integrating spin defects with photonic structures for new functionalities and higher emission rates. The article explores the potential applications of quantum sensing in several fields, such as superconductivity, ferromagnetism, 2D nanoelectronics, and biology. For instance, combining nanoscale microfluidic technology with nanopore and quantum sensing may lead to a new platform for DNA sequencing. As materials technology continues to evolve, and with the advancement of defect engineering techniques, 2D spin defects are expected to play a vital role in quantum sensing.

Fig. 1. An overview of quantum sensing with an optically accessible spin center.

Quantum sensing with optically accessible spin centers involves using paramagnetic defects in solids, such as nitrogen-vacancy (NV) centers in diamonds. Optically detected magnetic resonance (ODMR) is used to read the spin of solid-state color centers, which enables the creation of spin-based quantum sensors for measuring magnetic fields, electric fields, and temperature with high sensitivity. These sensors have broad applications in areas like microwave detection, superconductivity, and magnetic materials. Additionally, spin defects can be utilized in nanoscale nuclear magnetic resonance (NMR) spectroscopy. Ultrasensitive magnetometers can be used to perform nanoscale NMR. This technology has been used for detecting viruses, single proteins, and single protons

Fig. 2. Magnetic field sensing depends on the distance between the sample and the detecting spin.

a NV centers in diamonds that are aligned with the external magnetic field have sensing volumes that depend on their depth relative to the diamond’s surface. NV centers that are located closer to the diamond’s surface are more responsive to magnetic fields that are induced by the Larmor precession of nuclei from the sample outside of the diamond. b The dipolar fields originating from spins within a sample decrease exponentially with distance. Only spins that are located within a certain distance from a spin detector, like a nitrogen-vacancy center, will contribute to the measurable signal. The distance between the spin center and the surface of the sample material determines the effective spatial resolution. c Bringing a magnetometer into proximity to a field source provides a significant detection sensitivity advantage as the magnetic field strength decreases with distance according to ~1/r³. d Representation of the 3D crystal structure of diamond materials, showcasing their 3D atomic arrangement. e A monolayer of two-dimensional materials, which have an atomic thickness, benefits from the proximity effect, allowing for enhanced physical and electrical properties due to their proximity to other materials or fields

Fig. 3. Some representative works in the quantum defects within layered quantum materials and their development towards quantum sensing applications.

Given the rapid development of this field, we can only list part of them. For example, some of the research topics related to quantum emission from defects in transition metal dichalcogenides (TMDs)^–, room temperature single photon emitters in hBN, magnetic field-dependent photoluminescence, initialization and read-out of spin defects, nuclear spin polarization, quantum sensing imaging with layered materials (LMs), isotopic control of spin defects, and sensing in liquids. Figures adapted and reprinted with permission^,,,,,,,. Copyright by Springer Nature^,,,,,, American Physical Society, and American Chemical Society

Fig. 4. Representation of various spin defects.

a Depiction of the structural configuration of a boron vacancy (${\mathrm{V}}_B^{-}$) defect in hBN. b Zero-field ODMR spectrum of ${\mathrm{V}}_B^{-}$, showing resonance dips corresponding to spin transitions within the electronic state (in red), and the ground state (blue). c Simplified energy level structure of the ${\mathrm{V}}_B^{-}$ center in hBN^,. d Photoluminescence (PL) spectrum of an ensemble of carbon-related spin defects within hBN. e PL spectrum of an individual carbon-related spin defect. f ODMR of a carbon-related spin defect. g Calculated defect levels of Ti_VV defect in hBN. h Energy structure of the Ti_VV defect and their recombination rates. i Room temperature X-band EPR spectra of paramagnetic OB₃ in boron oxynitride (BNO) samples. Figures adapted and reprinted with permission from refs. ^,,,,. Copyright by Springer Nature^,,, and American Chemical Society

Fig. 5. Quantum sensing applications with 2D spin defects.

a Quantum sensing of nearby stray fields B_F produced by generated from Fe₃GeTe₂ (FGT). Two-dimensional maps show the static stray field B_F and the reconstructed magnetization 4 M of a suspended FGT slice, recorded at 6 K with a 142 G perpendicular magnetic field (B_ext). b Visualization of Joule heating and current density, stray magnetic fields in a graphene-based device using spin defects in hBN. c PL intensity distribution of a sensor array on the hBN flake. d An image and a schematic of a microfluidic channel integrated into a gold stripline microwave waveguide for quantum sensing in solution. Panel a, b are reproduced with permission from refs. ^,, respectively, Copyright by Springer Nature. Panel c is reproduced with permission from ref. , Copyright by American Institute of Physics. Panel c is reproduced with permission from ref. , Copyright by American Chemical Society

Fig. 6. Engineering quantum defects.

a–f Exploration of defect engineering techniques in two-dimensional (2D) materials, encompassing annealing, chemical treatments, ion, and electron irradiation, as well as focused beam, scanning tunneling microscopy (STM) tip, and laser writing methods for manipulating defects in 2D materials. g–j Focused ion beam write defect in layered materials. Reproduced with permission from ref. , Copyright by American Chemical Society. h Simulation of depth-dependent defect distribution using the stopping-and-range-of-ions-in-matter (SRIM) model, following the implantation of diverse ions such as He, C, N, and Ar. Reproduced with permission from ref. , Copyright by American Chemical Society. i Wield field and single-molecule localization microscopy of the isolated defect site. j Atomic force microscopy of the same region in (i). Reproduced with permission from ref. , Copyright by American Chemical Society. k–n Laser writing color centers in the hBN. Reproduced with permission from ref. , Copyright by Springer Nature

Fig. 7. Considerations and approaches for enhancing quantum sensing.

a Evaluation of spin defects for quantum sensing requires assessment of parameters including spin coherence, radiative recombination, intersystem crossing rates, energy level stability, and zero-field splitting. b The controlled generation of spin defects is critical and essential for the functionality of quantum sensing applications. c The proximity and surface effects significantly influence the sensing performance of two-dimensional spin defects. d The interaction between the spin and photonic structures may be leveraged to manipulate and enhance spin performance in quantum sensing^,. Panel d is reproduced with permission from refs. ^,, Copyright by American Chemical Society and Springer Nature, respectively

Fig. 8. Potential application of 2D spin defects.

a Schematic of a planar scanning probe microscope, in which the probe uses the spin center within 2D materials. b An optospintronic device is constructed from a heterostructure composed of a monolayer of WSe₂, a monolayer of graphene, and hBN deposited on a conventional SiO₂ substrate. With reproduce permission from, Copyright by American Chemical Society. c Different types of 2D materials. d The spin defects in 2D materials can be used to probe various phenomena in 2D nanodevices, like a spin wave, spin transport, ferromagnetic domain, and current flow in devices. e Sketch of using 2D spin defect in micro/nanofluidic devices. The plane illustrates a heterostructure nano-slit device. It overlays a super-resolved image showcasing masked ethanol-activated hexagonal boron nitride (hBN) and an atomic force microscopy (AFM) scan mapping the graphene spacers. Additionally, there is a super-resolved image that shows acetonitrile-activated emitters embedded within the nanoslits. Panel e is reproduced with permission from ref. , Copyright by Springer Nature. f Schematic of a quantum-enhanced DNA sequencing method by combining nanopore sequencing and quantum sensing using a 2D material membrane fabricated by a femtosecond laser to achieve high chemical resolution. The photo shows a nanopore in an hBN membrane fabricated by a femtosecond laser