Silicon-vacancy Color Centers Research Articles

Unraveling sources of emission heterogeneity in Silicon Vacancy color centers with cryo-cathodoluminescence microscopy

Diamond color centers have proven to be versatile quantum emitters and exquisite sensors of stress, temperature, electric and magnetic fields, and biochemical processes. Among color centers, the silicon-vacancy (SiV[Formula: see text]) defect exhibits high brightness, minimal phonon coupling, narrow optical linewidths, and high degrees of photon indistinguishability. Yet the creation of reliable and scalable SiV[Formula: see text]-based color centers has been hampered by heterogeneous emission, theorized to originate from surface imperfections, crystal lattice strain, defect symmetry, or other lattice impurities. Here, we advance high-resolution cryo-electron microscopy combined with cathodoluminescence spectroscopy and 4D scanning transmission electron microscopy (STEM) to elucidate the structural sources of heterogeneity in SiV[Formula: see text] emission from nanodiamond with sub-nanometer-scale resolution. Our diamond nanoparticles are grown directly on TEM membranes from molecular-level seedings, representing the natural formation conditions of color centers in diamond. We show that individual subcrystallites within a single nanodiamond exhibit distinct zero-phonon line (ZPL) energies and differences in brightness that can vary by 0.1 meV in energy and over 70% in brightness. These changes are correlated with the atomic-scale lattice structure. We find that ZPL blue-shifts result from tensile strain, while ZPL red shifts are due to compressive strain. We also find that distinct crystallites host distinct densities of SiV[Formula: see text] emitters and that grain boundaries impact SiV[Formula: see text] emission significantly. Finally, we interrogate nanodiamonds as small as 40 nm in diameter and show that these diamonds exhibit no spatial change to their ZPL energy. Our work provides a foundation for atomic-scale structure-emission correlation, e.g., of single atomic defects in a range of quantum and two-dimensional materials.

Core-shell diamond-graphene needles with silicon-vacancy color centers

Color centers in diamond nanostructures open new horizons in biomedicine, offering a biocompatible material platform for sensing temperature, pH, and magnetic field. Covering of the color centers enriched diamonds with graphene shell can essentially extend their application potential. Specifically, under irradiation with ultrashort laser pulses, the highly absorptive graphene shell can be used for excitation of a shock acoustic wave which can be used for cancer cell destruction or drug photoactivation through the Joule heating. In this study, we present a novel method for creating diamond-graphite core-shell structures. Through precise control of the growth of the graphitic layer on Single Crystal Diamond Needles (SCDNs) via vacuum annealing at 900°C for 30 minutes, we preserved 57% of the light emission from silicon-vacancy (SiV-) centers while maintaining their spectral peaks. Contrary to our expectations of reduced SiV- luminescence due to the presence of the graphitic shell, we observed that the initial high brightness of SiV- in the diamond needles persisted. This enabled us to detect SiV- luminescence spectrally, even within the core-shell structures. Our results underscore the tunability of these structures’ properties through temperature and duration control, suggesting promising prospects for their application in advanced biomedical tools with sensing capabilities.

Single-photon emission from silicon-vacancy color centers in polycrystalline diamond membranes

Single-color centers in thin polycrystalline diamond membranes allow the platform to be used in integrated quantum photonics, hybrid quantum systems, and other complex functional materials. While single-crystal diamond membranes are still technologically challenging to fabricate as they cannot be grown on a non-diamond substrate, free-standing polycrystalline diamond membranes can be conveniently fabricated at large-scale from nanocrystalline diamond seeds on a substrate that can be selectively etched. However, their practical application for quantum photonics is so far limited by crystallographic defects, impurities, graphitic grain boundaries, small grain sizes, scattering loss, and strain. In this paper, we report on a single-photon source based on silicon-vacancy color centers in a polycrystalline diamond membrane. We discuss the spectroscopic approach and quantify the photon statistics, obtaining a g2(0) ≈ 0.04. Our findings hold promise for introducing polycrystalline diamond to quantum photonics and hybrid quantum systems.

Qudit-Based Spectroscopy for Measurement and Control of Nuclear-Spin Qubits in Silicon Carbide.

Nuclear spins with hyperfine coupling to single electron spins are highly valuable quantum bits. Here we probe and characterize the particularly rich nuclear-spin environment around single silicon vacancy color centers (V2) in 4H-SiC. By using the electron spin-3/2 qudit as a four level sensor, we identify several sets of ^{29}Si and ^{13}C nuclear spins through their hyperfine interaction. We extract the major components of their hyperfine coupling via optical detected nuclear magnetic resonance, and assign them to shells in the crystal via the density function theory simulations. We utilize the ground-state level anticrossing of the electron spin for dynamic nuclear polarization and achieve a nuclear-spin polarization of up to 98±6%. We show that this scheme can be used to detect the nuclear magnetic resonance signal of individual spins and demonstrate their coherent control. Our work provides a detailed set of parameters and first steps for future use of SiC as a multiqubit memory and quantum computing platform.

Deterministic creation of strained color centers in nanostructures via high-stress thin films

Color centers have emerged as a leading qubit candidate for realizing hybrid spin-photon quantum information technology. One major limitation of the platform, however, is that the characteristics of individual color centers are often strain dependent. As an illustrative case, the silicon-vacancy center in diamond typically requires millikelvin temperatures in order to achieve long coherence properties, but strained silicon-vacancy centers have been shown to operate at temperatures beyond 1 K without phonon-mediated decoherence. In this work, we combine high-stress silicon-nitride thin films with diamond nanostructures to reproducibly create statically strained silicon-vacancy color centers (mean ground state splitting of 608 GHz) with strain magnitudes of ∼4×10−4. Based on modeling, this strain should be sufficient to allow for operation of a majority silicon-vacancy centers within the measured sample at elevated temperatures (1.5 K) without any degradation of their spin properties. This method offers a scalable approach to fabricate high-temperature operation quantum memories. Beyond silicon-vacancy centers, this method is sufficiently general that it can be easily extended to other platforms as well.

Silicon Vacancy in Boron-Doped Nanodiamonds for Optical Temperature Sensing.

Boron-doped nanodiamonds (BNDs) have recently shown a promising potential in hyperthermia and thermoablation therapy, especially in heating tumor cells. To remotely monitor eigen temperature during such operations, diamond color centers have shown a sensitive optical temperature sensing. Nitrogen-vacancy (NV) color center in diamonds have shown the best sensitivity in nanothermometry; however, spin manipulation of the NV center with green laser and microwave-frequency excitations is still a huge challenge for biological applications. Silicon-vacancy (SiV) color center in nano/bulk diamonds has shown a great potential to be a good replacement of the NV center in diamond as it can be excited and detected within the biological transparency window and its thermometry operations depends only on its zero-phonon line (ZPL) shift as a function of temperature changes. In this work, BNDs were carefully etched on smooth diamond nanocrystals' sharp edges and implanted with silicon for optical temperature sensing. Optical temperature sensing using SiV color centers in BNDs was performed over a small range of temperature within the biological temperature window (296-308 K) with an excellent sensitivity of 0.2 K in 10 s integration time. These results indicate that there are likely to be better application of more biocompatible BNDs in hyperthermia and thermoablation therapy using a biocompatible diamond color center.

Nanoscale thermal control of a single living cell enabled by diamond heater-thermometer

We report a new approach to controllable thermal stimulation of a single living cell and its compartments. The technique is based on the use of a single polycrystalline diamond particle containing silicon-vacancy (SiV) color centers. Due to the presence of amorphous carbon at its intercrystalline boundaries, such a particle is an efficient light absorber and becomes a local heat source when illuminated by a laser. Furthermore, the temperature of such a local heater is tracked by the spectral shift of the zero-phonon line of SiV centers. Thus, the diamond particle acts simultaneously as a heater and a thermometer. In the current work, we demonstrate the ability of such a Diamond Heater-Thermometer (DHT) to locally alter the temperature, one of the numerous parameters that play a decisive role for the living organisms at the nanoscale. In particular, we show that the local heating of 11–12 °C relative to the ambient temperature (22 °C) next to individual HeLa cells and neurons, isolated from the mouse hippocampus, leads to a change in the intracellular distribution of the concentration of free calcium ions. For individual HeLa cells, a long-term (about 30 s) increase in the integral intensity of Fluo-4 NW fluorescence by about three times is observed, which characterizes an increase in the [Ca2+]cyt concentration of free calcium in the cytoplasm. Heating near mouse hippocampal neurons also caused a calcium surge—an increase in the intensity of Fluo-4 NW fluorescence by 30% and a duration of ~ 0.4 ms.

Modular chip-integrated photonic control of artificial atoms in diamond waveguides

A central goal in creating long-distance quantum networks and distributed quantum computing is the development of interconnected and individually controlled qubit nodes. Atom-like emitters in diamond have emerged as a leading system for optically networked quantum memories, motivating the development of visible-spectrum, multi-channel photonic integrated circuit (PIC) systems for scalable atom control. However, it has remained an open challenge to realize optical programmability with a qubit layer that can achieve high optical detection probability over many optical channels. Here, we address this problem by introducing a modular architecture of piezoelectrically actuated atom-control PICs (APICs) and artificial atoms embedded in diamond nanostructures designed for high-efficiency free-space collection. The high-speed four-channel APIC is based on a splitting tree mesh with triple-phase shifter Mach–Zehnder interferometers. This design simultaneously achieves optically broadband operation at visible wavelengths, high-fidelity switching (>40dB) at low voltages, submicrosecond modulation timescales (>30MHz), and minimal channel-to-channel crosstalk for repeatable optical pulse carving. Via a reconfigurable free-space interconnect, we use the APIC to address single silicon vacancy color centers in individual diamond waveguides with inverse tapered couplers, achieving efficient single photon detection probabilities (∼15%) and second-order autocorrelation measurements g(2)(0)<0.14 for all channels. The modularity of this distributed APIC–quantum memory system simplifies the quantum control problem, potentially enabling further scaling to thousands of channels.

On the interpretation of confocal spectral depth profiling of color center and carrier concentration by photoluminescence and Raman of implanted 4H–SiC

Point defects in silicon carbide (SiC) formed after ion implantation can serve as color centers for quantum sensing, or as donors or acceptors to provide carriers to influence electrical performance. Confocal spectroscopic characterization allows the determination of point defect-related optical and electrical properties without sample preparation or destruction. However, phenomena such as refraction and aberration can complicate the interpretation of the results of three-dimensional spectroscopy. Here, we used H+, N+ and He+ implantation to fabricate silicon vacancy (VSi) color centers in SiC and used confocal spectroscopy to characterize bulk and thin layer of VSi contained materials. 270 keV H+ is more advantageous than 150 keV N+ in preparing VSi due to the preservation of better lattice integrity. For thin-layer VSi samples, the photoluminescence intensity maxima of VSi were distributed at 2–6.5 μm above the surface. To explain such confusing phenomenon in depth profiles focusing on and above the surface the effective excitation volume and chromatic aberration are discussed and proposed for explanation of the results. Furthermore, the ion-implanted layer exhibits a non-negligible effect on the underlying signal during confocal spectral depth profiling, which is attributed to the refraction-related focus degradation.

Silicon Vacancy Color Centers in 6H-SiC Fabricated by Femtosecond Laser Direct Writing

As a single photon source, silicon vacancy (VSi) centers in wide bandgap semiconductor silicon carbide (SiC) are expected to be used in quantum technology as spin qubits to participate in quantum sensing and quantum computing. Simultaneously, the new direct femtosecond (fs) laser writing technology has been successfully applied to preparing VSis in SiC. In this study, 6H-SiC, which has been less studied, was used as the processed material. VSi center arrays were formed on the 6H-SiC surface using a 1030-nm-wavelength fs pulsed laser. The surface was characterized by white light microscopy, atomic force microscopy, and confocal photoluminescence (PL)/Raman spectrometry. The effect of fs laser energy, vector polarization, pulse number, and repetition rate on 6H-SiC VSi defect preparation was analyzed by measuring the VSi PL signal at 785-nm laser excitation. The results show that fs laser energy and pulse number greatly influence the preparation of the color center, which plays a key role in optimizing the yield of VSis prepared by fs laser nanomachining.

Optical properties of SiV and GeV color centers in nanodiamonds under hydrostatic pressures up to 180 GPa

The silicon-vacancy (SiV) and germanium-vacancy (GeV) centers in diamond have a sharp photoluminescence with high brightness. In this work, the photoluminescence of these centers is measured up to 180 GPa using nanodiamonds integrated in a diamond anvil cell. The results show blueshifts in the mean emission energy determined by the atomic radii of the impurity. The agreement with $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations based on the lattice compression of diamond demonstrates the potential of these centers for sensing under extreme pressure conditions.

SiV Centers Electroluminescence in Diamond Merged Diode

The results of a study of electroluminescence of silicon vacancy color centers (SiV centers) in a diamond merged diode with a structure involving parallel connection of a p–i–n diode and a Schottky diode are presented. To create color centers, the inner region of the diode is doped with silicon. In the luminescence spectrum, only a line at a wavelength of 738 nm is detected, corresponding to the emission of a SiV color center in a negative charge state. Emission at a wavelength of 946 nm, corresponding to the SiV color center in the neutral charge state, is not detected. The electroluminescence of color centers is observed only in the p–i–n region of the diode, that is, it is experimentally demonstrated that both types of charge carriers are necessary to excite electroluminescence. A pronounced dependence of the photoluminescence intensity of SiV centers on the applied voltage is found.

Divacancy and silicon vacancy color centers in 4H-SiC fabricated by hydrogen and dual ions implantation and annealing

Silicon carbide (SiC), as a wide-band gap semiconductor, plays an important role in high temperature and high-power devices, and the spin defect has great application prospect in quantum technology. Divacancy in SiC (VCVSi, VV) has attracted more and more attention. There are a lot of experimental studies on color center preparation by ion implantation, but the mechanism of atomic scale defects in the experimental preparation process is not fully understood. EPI epitaxial 4H–SiC was implanted with 250 keV proton at room temperature under three fluence of 1E14 cm−2, 1E15 cm−2, 1E16 cm−2. Defects of implanted 4H–SiC samples were characterized by photoluminescence spectrum and electron paramagnetic resonance (EPR). The existence of the optimal implantation fluence for VSi and VCVSi (VV) color centers by hydrogen ion implantation was found. Molecular dynamics (MD) simulation by considering the ionization energy loss for swift ion implantation were used to study the defect distribution and transformation at atomic-scale during hydrogen ion implantation and post-annealing. The optimal implantation fluence was found and confirmed by comparing the atomic-scale implantation simulation with the experimental results. In the annealing simulation, the optimal annealing temperature for the color centers in 4H–SiC was verified, and its formation mechanism was analyzed by accurately calculating the defect transformation during the annealing process. Finally, in order to accurately control the depth of color center in 4H–SiC, dual ions implantation of carbon and proton has been studied to realize the optimal divacancy yield by SRIM and MD simulations. Molecular dynamics simulation results showed that low-fluence C pre-implantation is helpful to improve the color center yield for the dual ions implantation.

All‐Optical Thermometry with NV and SiV Color Centers in Biocompatible Diamond Microneedles (Advanced Optical Materials 15/2022)

Biocompatible single-crystal diamond needles enriched with nitrogen and silicon vacancy (NV and SiV) color centers in a controllable manner via modified chemical vapor deposition synthesis are employed by Lena Golubewa, Polina Kuzhir and co-workers (article number 2200631) for improved all-optical thermometry based on the temperature dependence of SiV zero-phonon-line (ZPL) peak position, FWHM, photoluminescence lifetime, and ratiometrically determined ZPL intensity. Simultaneous spectrally separated bioimaging with both color centers is performed.

Protected two-qubit entangling gate with mechanical driven continuous dynamical decoupling

In this work, we propose a high-fidelity phonon-mediated entangling gate in a hybrid mechanical system based on two silicon-vacancy color centers in diamond. In order to suppress the influence of the spin decoherence on the entangling gate, we use a continuous dynamical decoupling approach to create new dressed spin states, which are less sensitive to environmental fluctuations and exhibit an extended spin dephasing time. The effective spin–spin Hamiltonian modified by the mechanical driving field and the corresponding master equation are derived in the dispersive regime. We show that in the presence of the mechanical driving field, the effective spin–spin coupling can be highly controlled. By calculating the entangling gate fidelity in the dressed basis, we find that once the mechanical field is turned on, the gate fidelity can be significantly improved. In particular, under an optimized spin-phonon detuning and a stronger Rabi frequency of the mechanical driving field, the two-qubit gate is capable of reaching fidelity exceeding 0.99. Moreover, by employing appropriate driving modulation, we show that a high-fidelity full quantum gate can be also realized, in which the initial and final spin states are on a bare basis. Our work provides a promising scheme for realizing high-fidelity quantum information processing.

All‐Optical Thermometry with NV and SiV Color Centers in Biocompatible Diamond Microneedles

AbstractMonitoring of tiny intracell temperature variations is of high importance to understand the mechanisms of exothermic/endothermic processes inside the living cells. Small shifts in thermal balance may drastically influence cell functioning and induce pathological conditions. By using biocompatible diamond single‐crystal microneedles enriched with nitrogen‐vacancy (NV)/silicon‐vacancy (SiV) color centers, this study demonstrates all‐optical in vitro temperature monitoring in the physiologically significant range (25–55 °C). Zero‐phonon line (ZPL) of SiV centers belonging to the “therapeutic window” is used to improve measurement precision via suppression of the tissue autofluorescence. The simultaneous detection of the NV and SiV fluorescence enables two‐band visualization of the living cells combined with the temperature sensing. This study demonstrates experimentally that temperature can be measured by lifetime, full‐width at half maximum, and peak position of SiV ZPL, while accuracy can be further improved by normalizing the photoluminescence (PL) ZPL peak intensity on the PL signal measured at the wavelength where it is temperature independent. According to performed numerical simulations diamond microneedles enable real‐time temperature measurements because their characteristic heating time is less than 10 ns. The results open a way toward accurate, noninvasive, precise, and real‐time monitoring of temperature variations accompanying intracellular biochemical reactions and processes on the single‐cell level.

Coherent Interactions between Silicon-Vacancy Centers in Diamond.

We report tunable excitation-induced dipole-dipole interactions between silicon-vacancy color centers in diamond at cryogenic temperatures. These interactions couple centers into collective states, and excitation-induced shifts tag the excitation level of these collective states against the background of excited single centers. By characterizing the phase and amplitude of the spectrally resolved interaction-induced signal, we observe oscillations in the interaction strength and population state of the collective states as a function of excitation pulse area. Our results demonstrate that excitation-induced dipole-dipole interactions between color centers provide a route to manipulating collective intercenter states in the context of a congested, inhomogeneous ensemble.

Nonreciprocal Phonon Blockade in a Spinning Acoustic Ring Cavity Coupled to a Two-Level System

Quantum nonreciprocal devices have received extensive attention in recent years because they can be used to realize unidirectional quantum routing and noise isolation. In this work, we show that the shift of resonance frequencies of propagating phonons induced by spin-orbit interactions (SOI) of phonons in a rotating acoustic ring cavity can be used to realize nonreciprocal phonon blockade. When driving the cavity from different directions, nonreciprocal single-, two-phonon blockade and phonon-induced tunneling can take place by varying the parameters of the system to an appropriate value. To realize phonon blockade, the sublevels of the lower orbit branch of the ground state of silicon-vacancy (SiV) color centers in the diamond membrane are employed to induce self-interactions of phonons in the cavity. This work provides a way to achieve acoustic nonreciprocal devices, such as directional acoustic switches and quantum noise isolation, which may help acoustic information network processing.

High-pressure high-temperature industrial preparation of micron-sized diamond single crystals with silicon-vacancy colour centres

Negatively charged silicon-vacancy (SiV−) colour centres are considered to be promising room-temperature single-photon sources. The controlled preparation of high-grade industrial diamonds containing a certain amount of SiV− colour centres remains a significant technical challenge. Herein, micron-sized industrial-grade diamonds containing different concentrations of SiV− colour centres were prepared by adjusting the doping amount of Si powder under the pressure conditions of 5.0–5.2 GPa and temperatures of 1420–1500 °C. Al was used as the nitrogen getter in FeNiCo−C systems through the diamond film growth method (FGM). The results show that the intensity of the SiV− colour centres in synthesized diamond increases with increases in the Si doping amount. It has also been proved that nitrogen impurities inhibit the formation of SiV− colour centres in diamond. In addition, the diamond Raman peak positions exhibit a redshift (from 1330.88 cm−1 to 1329.55 cm−1), and an increase in the Raman full width at half maximum (FWHM) (from 4.78 cm−1 to 5.17 cm−1), indicating that Si enters the diamond lattice, but the diamond crystals still have a single sp3 structure. Our research provides a fast, efficient and low-cost method for the controlled batch preparation of industrial-grade diamond containing SiV− colour centres.

Effect of boron doping on luminescent properties of silicon--vacancy and germanium--vacancy color centers in diamond particles obtained by chemical vapor deposition

The effect of doping with boron on the luminescent properties of diamond particles synthesized by Hot Filament Chemical Vapor Deposition technique with color centers embedded during the growth process has been studied. It is shown that at low boron doping level, the photoluminescence intensity of a narrow zero-phonon line of the silicon-vacancy color center (738.2 nm) demonstrates a strong dependence on the concentration of boron atoms at the sites of the diamond lattice. The dependence of the intensity of a broad photoluminescence band in the wavelength range 520-800 nm on the concentration of boron atoms in the gas mixture in the range from 14 to 64000 ppm has been analyzed. The Raman scattering spectra of the obtained particles have been studied. At the concentration of boron atoms in the gas mixture up to 1540 ppm, the Raman scattering spectra of diamond particles practically do not change when the boron concentration is varied. At high boron doping level, the diamond band in the Raman spectra exhibit a spectral response typical of the Fano resonance. Keywords: diamond particles, color centers, boron doping, photoluminescence, chemical vapor deposition.