Efficiency Optimization of Ge-V Quantum Emitters in Single-Crystal Diamond upon Ion Implantation and HPHT Annealing

The authors report on the characterization at the single-defect level of germanium-vacancy (GeV) centers in diamond produced upon Ge− ion implantation and different subsequent annealing processes, with a specific focus on the effect of high-pressure-high-temperature (HPHT) processing on their quantum-optical properties. Different post-implantation annealing conditions are explored for the optimal activation of GeV centers, namely, 900 °C 2 h, 1000 °C 10 h, 1500 °C 1 h under high vacuum, and 2000 °C 15 min at 6 GPa pressure. A systematic analysis of the relevant emission properties, including the emission intensity in saturation regime and the excited state radiative lifetime, is performed on the basis of a set of ion-implanted samples, with the scope of identifying the most suitable conditions for the creation of GeV centers with optimal quantum-optical emission properties. The main performance parameter adopted here to describe the excitation efficiency of GeV centers as single-photon emitters is the ratio between the saturation optical excitation power and the emission intensity at saturation. The results show an up to eightfold emission efficiency increase in HPHT-treated samples with respect to conventional annealing in vacuum conditions, suggesting a suitable thermodynamic pathway toward the repeatable fabrication of ultra-bright GeV centers for single-photon generation purposes

Ultrastrong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers

The critical step for future quantum industry demands realization of efficient information exchange between different-platform hybrid systems that can harvest advantages of distinct platforms. The major restraining factor for the progress in certain hybrids is weak coupling strength between the elemental particles. In particular, this restriction impedes a promising field of hybrid magnonics. In this work, we propose an approach for realization of on-chip hybrid magnonic systems with unprecedentedly strong coupling parameters. The approach is based on multilayered microstructures containing superconducting, insulating, and ferromagnetic layers with modified photon phase velocities and magnon eigenfrequencies. The enhanced coupling strength is provided by the radically reduced photon mode volume. Study of the microscopic mechanism of the photon-to-magnon coupling evidences formation of the long-range superconducting coherence via thick strong ferromagnetic layers in superconductor/ferromagnet/superconductor trilayer in the presence of magnetization precession. This discovery offers new opportunities in microwave superconducting spintronics for quantum technologies

Effect of Nitrogen Impurities on the Raman Line Width in Diamond, Revisited

The results of a high-resolution Raman scattering study of a diamond crystal with a high content of single substitutional nitrogen impurities (550 ppm) in the temperature range from 50 to 673 K are presented and compared with the data for defect-free diamond. It is established that the increase of the nitrogen concentration in diamond leads to the temperature-independent increase of the Raman line width. Analysis of the experimental data allows us to conclude that this broadening should be attributed to the defect-induced shortening of the Raman phonon lifetime. We believe that this mechanism is responsible for the increase of the Raman line width caused by most point-like defects in diamond. No pronounced effects of the nitrogen defects on the Raman line position and phonon anharmonicity are observed

Water Speciation and Storage Capacity of Olivine under the Reduced Fluid—Peridotite Interaction

The key features of the interaction between peridotites of the continental lithospheric mantle and reduced hydrocarbon-rich fluids have been studied in experiments conducted at 5.5 GPa and 1200 °C. Under this interaction, the original harzburgite undergoes recrystallization while the composition of the fluid changes from CH4-H2O to H2O-rich with a small amount of CO2. The oxygen fugacity in the experiments varied from the iron-wustite (IW) to enstatite-magnesite-olivine-graphite/diamond (EMOG) buffers. Olivines recrystallized in the interaction between harzburgite and a fluid generated by the decomposition of stearic acid contain inclusions composed of graphite and methane with traces of ethane and hydrogen. The water content of such olivines slightly exceeds that of the original harzburgite. Redox metasomatism, which involves the oxidation of hydrocarbons in the fluid by reaction with magnesite-bearing peridotite, leads to the appearance of additional OH absorption bands in the infrared spectra of olivines. The water content of olivine in this case increases by approximately two times, reaching 160–180 wt. ppm. When hydrocarbons are oxidized by interaction with hematite-bearing peridotite, olivine captures Ca-Mg-Fe carbonates, which are products of carbonate melt quenching. This oxidative metasomatism is characterized by the appearance of specific OH absorption bands and a significant increase in the total water content in olivine of up to 500–600 wt. ppm. These findings contribute to the development of criteria for reconstructing metasomatic transformations in mantle rocks based on the infrared spectra and water content of olivines

Effect of Rare-Earth Element Oxides on Diamond Crystallization in Mg-Based Systems

Diamond crystallization in Mg-R2O3-C systems (R = Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, and Yb) was studied at 7.8 GPa and 1800 °C. It was found that rare-earth oxide additives in an amount of 10 wt % did not significantly affect both the degree of graphite-to-diamond conversion and crystal morphology relative to the Mg-C system. The effect of higher amounts of rare-earth oxide additives on diamond crystallization was studied for a Mg-Sm2O3-C system with a Sm2O3 content varied from 0 to 50 wt %. It was established that with an increase in the Sm2O3 content in the growth system, the degree of graphite-to-diamond conversion decreased from 80% at 10% Sm2O3 to 0% at 40% Sm2O3. At high Sm2O3 contents (40 and 50 wt %), instead of diamond, mass crystallization of metastable graphite was established. The observed changes in the degree of the graphite-to-diamond conversion, the changeover of diamond crystallization to the crystallization of metastable graphite, and the changes in diamond crystal morphology with increasing the Sm2O3 content attested the inhibiting effect of rare-earth oxides on diamond crystallization processes in the Mg-Sm-O-C system. The crystallized diamonds were studied by a suite of optical spectroscopy techniques, and the major characteristics of their defect and impurity structures were revealed. For diamond crystals produced with 10 wt % and 20 wt % Sm2O3 additives, a specific photoluminescence signal comprising four groups of lines centered at approximately 580, 620, 670, and 725 nm was detected, which was tentatively assigned to emission characteristic of Sm3+ ions

Effect of HPHT Treatment on Spectroscopic Features of Natural Type Ib-IaA Diamonds Containing Y Centers

In this paper, we report a spectroscopic study of natural type Ib-IaA diamonds containing Y centers subjected to high-pressure high-temperature treatment at 7–7.5 GPa and 1700–2200 °C. Diamond samples showing the Y centers as the dominant absorption feature in the infrared spectra were selected from a collection of natural diamonds from alluvial placers of the northeastern Siberian Platform. The samples were investigated by spectroscopic techniques before and after each annealing stage. It was found that upon annealing at temperatures higher than 2000°C, the defect-induced one-phonon spectra changed from the Y centers to a new form with a characteristic band peaking at 1060 cm−1. Photoluminescence spectra of the samples were modified after each annealing stage starting from 1700 °C. The most significant changes in photoluminescence occurred at temperatures higher than 2000 °C and were associated with a sharp increase of the intensity of an emission band peaking at about 690 nm. A comparison with natural red-luminescing diamonds from Yakutian kimberlite pipes was performed. It was concluded that the observed 1060 cm−1 IR band and the 690 nm red emission band are genetically related to the Y centers and that defects or impurities responsible for the Y centers appear quite widespread in natural diamonds from various deposits worldwide

Crystallization of Diamond from Melts of Europium Salts

Diamond crystallization in melts of europium salts (Eu2(C2O4)3·10H2O, Eu2(CO3)3·3H2O, EuCl3, EuF3, EuF2) at 7.8 GPa and in a temperature range of 1800–2000 °C was studied for the first time. Diamond growth on seed crystals was realized at a temperature of 2000 °C. Spontaneous diamond nucleation at these parameters was observed only in an Eu oxalate melt. The maximum growth rate in the europium oxalate melt was 22.5 μm/h on the {100} faces and 12.5 μm/h on the {111} faces. The diamond formation intensity in the tested systems was found to decrease in the following sequence: Eu2(C2O4)3·10H2O > Eu2(CO3)3·3H2O > EuF3 > EuF2 = EuCl3. Diamond crystallization occurred in the region of stable octahedral growth in melts of Eu3+ salts and in the region of cubo-octahedral growth in an EuF2 melt. The microrelief of faces was characterized by specific features, depending on the system composition and diamond growth rate. In parallel with diamond growth, the formation of metastable graphite in the form of independent crystals and inclusions in diamond was observed. From the spectroscopic characterization, it was found that diamonds synthesized from Eu oxalate contain relatively high concentrations of nitrogen (about 1000−1200 ppm) and show weak PL features due to inclusions of Eu-containing species