Deterministic placement of ultra-bright near-infrared color centers in arrays of silicon carbide micropillars

7D High-Dynamic Spin-Multiplexing

Multiplexing technology creates several orthogonal data channels and dimensions for high-density information encoding and is irreplaceable in large-capacity information storage, and communication, etc. The multiplexing dimensions are constructed by light attributes and spatial dimensions. However, limited by the degree of freedom of interaction between light and material structure parameters, the multiplexing dimension exploitation method is still confused. Herein, a 7D Spin-multiplexing technique is proposed. Spin structures with four independent attributes (color center type, spin axis, spatial distribution, and dipole direction) are constructed as coding basic units. Based on the four independent spin physical effects, the corresponding photoluminescence wavelength, magnetic field, microwave, and polarization are created into four orthogonal multiplexing dimensions. Combined with the 3D of space, a 7D multiplexing method is established, which possesses the highest dimension number compared with 6 dimensions in the previous study. The basic spin unit is prepared by a self-developed laser-induced manufacturing process. The free state information of spin is read out by four physical quantities. Based on the multiple dimensions, the information is highly dynamically multiplexed to enhance information storage efficiency. Moreover, the high-dynamic in situ image encryption/marking is demonstrated. It implies a new paradigm for ultra-high-capacity storage and real-time encryption.

Quantum systems in silicon carbide for sensing applications

This paper summarizes recent studies identifying key qubit systems in silicon carbide (SiC) for quantum sensing of magnetic, electric fields, and temperature at the nano and microscale. The properties of colour centres in SiC, that can be used for quantum sensing, are reviewed with a focus on paramagnetic colour centres and their spin Hamiltonians describing Zeeman splitting, Stark effect, and hyperfine interactions. These properties are then mapped onto various methods for their initialization, control, and read-out. We then summarised methods used for a spin and charge state control in various colour centres in SiC. These properties and methods are then described in the context of quantum sensing applications in magnetometry, thermometry, and electrometry. Current state-of-the art sensitivities are compiled and approaches to enhance the sensitivity are proposed. The large variety of methods for control and read-out, combined with the ability to scale this material in integrated photonics chips operating in harsh environments, places SiC at the forefront of future quantum sensing technology based on semiconductors.

Metal-Dielectric Nanopillar Antenna-Resonators for Efficient Collected Photon Rate from Silicon Carbide Color Centers

A yet unresolved challenge in developing quantum technologies based on color centres in high refractive index semiconductors is the efficient fluorescence enhancement of point defects in bulk materials. Optical resonators and antennas have been designed to provide directional emission, spontaneous emission rate enhancement and collection efficiency enhancement at the same time. While collection efficiency enhancement can be achieved by individual nanopillars or nanowires, fluorescent emission enhancement is achieved using nanoresonators or nanoantennas. In this work, we optimise the design of a metal-dielectric nanopillar-based antenna/resonator fabricated in a silicon carbide (SiC) substrate with integrated quantum emitters. Here we consider various color centres known in SiC such as silicon mono-vacancy and the carbon antisite vacancy pair, that show single photon emission and quantum sensing functionalities with optical electron spin read-out, respectively. We model the dipole emission fluorescence rate of these color centres into the metal-dielectric nanopillar hybrid antenna resonator using multi-polar electromagnetic scattering resonances and near-field plasmonic field enhancement and confinement. We calculate the fluorescence collected photon rate enhancement for these solid state vacancy-centers in SiC in these metal-dielectric nanopillar resonators, showing a trade-off effect between the collection efficiency and radiative Purcell factor enhancement. We obtained a collected photon rate enhancement from a silicon monovacancy vacancy center embedded in an optimised hybrid antenna-resonator two orders of magnitude larger compared to the case of the color centres in bulk material.

Photon extraction enhancement of praseodymium ions in gallium nitride nanopillars

Lanthanoid-doped Gallium Nitride (GaN) integrated into nanophotonic technologies is a promising candidate for room-temperature quantum photon sources for quantum technology applications. We manufactured praseodymium (Pr)-doped GaN nanopillars of varying size, and showed significantly enhanced room-temperature photon extraction efficiency compared to unstructured Pr-doped GaN. Implanted Pr ions in GaN show two main emission peaks at 650.3 nm and 651.8 nm which are attributed to ³P₀-³F₂ transition in the 4f-shell. The maximum observed enhancement ratio was 23.5 for 200 nm diameter circular pillars, which can be divided into the emitted photon extraction enhancement by a factor of 4.5 and the photon collection enhancement by a factor of 5.2. The enhancement mechanism is explained by the eigenmode resonance inside the nanopillar. Our study provides a pathway for Lanthanoid-doped GaN nano/micro-scale photon emitters and quantum technology applications.

Optical and Spin Properties of NV Center Ensembles in Diamond Nano-Pillars

Nitrogen-vacancy (NV) color centers in diamond are excellent quantum sensors possessing high sensitivity and nano-scale spatial resolution. Their integration in photonic structures is often desired, since it leads to an increased photon emission and also allows the realization of solid-state quantum technology architectures. Here, we report the fabrication of diamond nano-pillars with diameters up to 1000 nm by electron beam lithography and inductively coupled plasma reactive ion etching in nitrogen-rich diamonds (type Ib) with [100] and [111] crystal orientations. The NV centers were created by keV-He ion bombardment and subsequent annealing, and we estimate an average number of NVs per pillar to be 4300 ± 300 and 520 ± 120 for the [100] and [111] samples, respectively. Lifetime measurements of the NVs’ excited state showed two time constants with average values of τ₁ ≈ 2 ns and τ₂ ≈ 8 ns, which are shorter as compared to a single color center in a bulk crystal (τ ≈ 10 ns). This is probably due to a coupling between the NVs as well as due to interaction with bombardment-induced defects and substitutional nitrogen (P1 centers). Optically detected magnetic resonance measurements revealed a contrast of about 5% and average coherence and relaxation times of T₂ [100] = 420 ± 40 ns, T₂ [111] = 560 ± 50 ns, and T₁ [100] = 162 ± 11 μs, T₁ [111] = 174 ± 24 μs. These pillars could find an application for scanning probe magnetic field imaging.

Hexagonal boron nitride: a review of the emerging material platform for single-photon sources and the spin-photon interface

Single-photon sources and their optical spin readout are at the core of applications in quantum communication, quantum computation, and quantum sensing. Their integration in photonic structures such as photonic crystals, microdisks, microring resonators, and nanopillars is essential for their deployment in quantum technologies. While there are currently only two material platforms (diamond and silicon carbide) with proven single-photon emission from the visible to infrared, a quantum spin-photon interface, and ancilla qubits, it is expected that other material platforms could emerge with similar characteristics in the near future. These two materials also naturally lead to monolithic integrated photonics as both are good photonic materials. While so far the verification of single-photon sources was based on discovery, assignment and then assessment and control of their quantum properties for applications, a better approach could be to identify applications and then search for the material that could address the requirements of the application in terms of quantum properties of the defects. This approach is quite difficult as it is based mostly on the reliability of modeling and predicting of color center properties in various materials, and their experimental verification is challenging. In this paper, we review some recent advances in an emerging material, low-dimensional (2D, 1D, 0D) hexagonal boron nitride (h-BN), which could lead to establishing such a platform. We highlight the recent achievements of the specific material for the expected applications in quantum technologies, indicating complementary outstanding properties compared to the other 3D bulk materials.