Thin films with quantum defects are emerging as a potential platform for quantum applications. Quantum defects in some thin films arise due to structural imperfections, such as vacancies or impurities. These defects generate localized electronic states with unique optical and electronic properties. Crystal vacancies or defects that occur when atoms are missing from a crystal lattice can influence a material's quantum properties. In this study, we investigated inexpensive, complementary metal oxide semiconductor compatible materials with quantum defects suitable for room temperature applications. The experiments indicated 5, 15, and 17 ns relaxation times for aluminum nitride, aluminum oxide or alumina, and tin oxides, respectively. For all these materials, distinct resonant peaks are observed at approximately 1.1, 1.6, 2.2, and 2.7 GHz at room temperature (i.e., 21 °C). These peaks exhibit slight frequency shifts, corresponding to known defect locations and thin film material properties. This discovery may lead the way to reliable, cost-effective quantum applications in our daily lives.
Thin films with quantum defects are emerging as a potential platform for quantum applications. Quantum defects in some thin films arise due to structural imperfections, such as vacancies or impurities. These defects generate localized electronic states with unique optical and electronic properties. Crystal vacancies or defects that occur when atoms are missing from a crystal lattice can influence a material's quantum properties. In this study, we investigated inexpensive, complementary metal oxide semiconductor compatible materials with quantum defects suitable for room temperature applications. The experiments indicated 5, 15, and 17 ns relaxation times for aluminum nitride, aluminum oxide or alumina, and tin oxides, respectively. For all these materials, distinct resonant peaks are observed at approximately 1.1, 1.6, 2.2, and 2.7 GHz at room temperature (i.e., 21 °C). These peaks exhibit slight frequency shifts, corresponding to known defect locations and thin film material properties. This discovery may lead the way to reliable, cost-effective quantum applications in our daily lives.
The development of quantum technologies is generating great interest, as they promise major breakthroughs in computational power, measurement sensitivity and precision, as well as communication security, with potential applications acrossdiverse fields such as healthcare or electronics. In this context, rare-earth-doped oxide thin films represent a competitivesolid-state quantum platform for light–matter interactions. This is due to the ability of rare-earth ions to exhibit quantumcoherent states with long coherence times, combined with the nanometric thickness of the films, which makes them compatible with diverse photonic architectures. Chemical vapor deposition (CVD) offers a fast and cost-effective techniquefor producing thin films with good crystalline quality. However, compared to bulk crystals and ceramics, their propertiesare often degraded, likely due to surface proximity, a higher density of point defects, and strain. The use of epitaxial thinfilms, with a reduced defect density, is expected to lead to improved coherence times. The aim of this PhD project istherefore to obtain epitaxial CVD thin films and to enhance their crystalline properties in order to achieve light–matterinterfaces with long coherence times. Thin films were grown on various substrates, including silicon, oxides (quartz, sapphire, yttria-stabilized zirconia, YSZ), and hybrid substrates with a first layer deposited by molecular beam epitaxy (MBE).In parallel, the influence of post-deposition annealing treatments on the crystalline and optical properties of the films wasinvestigated. Epitaxy on hybrid substrates and YSZ was confirmed, with optical coherence times (T2) of 1.1 µs and 0.8µs, respectively, more than twenty times longer than those measured in polycrystalline films of equivalent composition.This epitaxial architecture paves the way for nanostructuring and integration into photonic devices such as resonators andwaveguides.
Defect based qubit systems like the nitrogen vacancy center in diamond have recently emerged as promising candidates for quantum technologies due to their combination of long coherence times, room temperature operation, and robust optical interface. In order to realize many of their proposed applications, defect qubits must be incorporated into scalable devices architectures consisting of photonic, mechanical, or electrical degrees of freedom. Despite much recent progress, many challenges remain for diamond growth and device fabrication. As an alternate approach, we engaged in a search for nitrogen vacancy center analogues in alternative materials with the hope of obtaining a greater degree of control over defect and material properties. Ultimately, we discovered that divacancy-related point defects in all three of the most common forms of silicon carbide- termed 4H, 6H, and 3C- act as analogues to the nitrogen vacancy center in diamond. We chose to focus our research primarily on defects in 3C silicon carbide (termed 'Ky5' defects) because of its availability as a single crystal heteroepitaxial thin film grown on silicon, an advantage that greatly facilitates the fabrication of functional devices. We characterized the spin and optical properties of Ky5 defects in thin film geometries and observed many similarities to the nitrogen vacancy center. We performed the first measurements of spin dynamics in 3C silicon carbide and demonstrate coherent control of defect spins up to room temperature and observe coherence times of up to 22 microseconds. To demonstrate their use in real devices, we designed, fabricated, and characterized photonic crystal cavities in 3C silicon carbide thin films with mode volumes of less than (lambda/n)^3 and Q's as high as 1,500 with integrated Ky5 defects. Additionally, we performed simulations and analysis of the fabricated structures using observed structural imperfections to determine that the Q's are likely limited primarily by the non-vertical structure sidewall angle. Despite the modest Q's of these structures, they can be utilized to generate large local field intensities to enhance optical interactions with Ky5 qubit states within the cavities. We accomplish this by performing cavity enhanced photoluminescence excitation spectroscopy on cavity modes tuned to the zero phonon line of the defects and observe large (as high as 30 times) increases in the luminescence and optically detected magnetic resonance signals originating from the defect states and approximately 2x faster rates of ground state spin initialization. In addition, we use these techniques to probe the photoluminescence dynamics of the Ky5 defects' optical pumping cycle, perform excitation wavelength dependent studies of spin and spectral inhomogeneity, and use the small mode volume and narrowband photoluminescence enhancements of the cavities to observe spectrally distinct subensembles of defects with linewidths as narrow as 25 GHz within the inhomogeneously broadened zero phonon line. Although much is still unknown regarding the properties of these defects, they show great promise as a candidate system for defect qubit based quantum devices and technologies.
Abstract A way of obtaining new thin-film materials for forming photon echoes at room temperature on special exciton states in thin textured films obtained via magnetron sputtering is proposed, along with a model that explains the properties of new states and is associated with the formation of special exciton states. The dependence of the relaxation times of resonant transitions on the size of nanoscale clusters of surface defects is investigated for different film thicknesses and various semiconductor materials. Prospects for using such materials in medical technology are determined.
Experimental results of observations of a femtosecond photon echo excited in an ensemble of quantum nanometer-sized objects in thin semiconductor (ZnO, SiB, SiP) films at room temperature are presented. The observed properties of the photon echo are discussed. Recorded relaxation times of exciton quantum transitions and beats at the photon echo decay as a function of the increasing interval between the exciting pulses reveal the role played by the defects of the thin film in the formation of its exciton structure of quantum transitions investigated using angular optical echo spectroscopy.
Abstract Optically active point defects in wide‐bandgap crystals are leading building blocks for quantum information technologies including quantum processors, repeaters, simulators, and sensors. Although defects and impurities are ubiquitous in all materials, select defect configurations in certain materials harbor coherent electronic and nuclear quantum states that can be optically and electronically addressed in solid‐state devices, in some cases even at room temperature. Historically, the study of quantum point defects has been limited to a relatively small set of host materials and defect systems. In this article, we consider the potential for identifying defects in new materials, either to advance known applications in quantum science or to enable entirely new capabilities. We propose that, in principle, it should be possible to reverse the historical approach, which is partially based on accidental discovery, in order to design quantum defects with desired properties suitable for specific applications. We discuss the biggest obstacles on the road towards this goal, in particular those related to theoretical prediction, materials growth and processing, and experimental characterization.
Abstract The nitrogen-vacancy (NV) color center in diamond has demonstrated great promise in a wide range of quantum sensing. Recently, there have been a series of proposals and experiments using NV centers to detect spin noise of quantum materials near the diamond surface. This is a rich complex area of study with novel nano-magnetism and electronic behavior, that the NV center would be ideal for sensing. However, due to the electronic properties of the NV itself and its host material, getting high quality NV centers within nanometers of such systems is challenging. Band bending caused by space charges formed at the metal-semiconductor interface force the NV center into its insensitive charge states. Here, we investigate optimizing this interface by depositing thin metal films and thin insulating layers on a series of NV ensembles at different depths to characterize the impact of metal films on different ensemble depths. We find an improvement of coherence and dephasing times we attribute to ionization of other paramagnetic defects. The insulating layer of alumina between the metal and diamond provide improved photoluminescence and higher sensitivity in all modes of sensing as compared to direct contact with the metal, providing as much as a factor of 2 increase in sensitivity, decrease of integration time by a factor of 4, for NV T 1 relaxometry measurements.