arXiv subjects

G. V. Astakhov

Publications and source records attributed to G. V. Astakhov.

At least 19 recordsLinked to original sources

arXiv2026

Telecom-band quantum memory with chlorine defects in silicon carbide

Realization of quantum memory with a photonic interface in the telecommunication bands in a wafer-scalable platform is a central requirement for long-distance quantum networks. Silicon carbide (SiC) provides a technologically mature host for integrated quantum photonics, yet only a limited number of defects combine spin functionality with telecom emission. Here we report on chlorine-based defects in 4H-SiC as a platform for telecom-band quantum memory. The emission of these defects spans the entire telecommunication range with zero-phonon lines in the O- and C-bands and a Debye-Waller factor of up to $39 \, \%$. Time-resolved photoluminescence measurements reveal a short excited-state lifetime in the sub-nanosecond range. We demonstrate that these defects are spin-active even at room temperature, exhibiting optically detected magnetic resonances (ODMR) in the sub-GHz frequency range. Using ODMR spectroscopy and Ramsey interferometry, we resolve the hyperfine structure arising from the interaction with $^{35}\mathrm{Cl}$ nuclear spins. The ODMR spectra exhibit complex behaviour in an external magnetic field due to mixing of electron-nuclear spin states, which is well reproduced by our simulations. The spin relaxation and coherence times are in the sub-microsecond range, limited by rapid quenching of the ODMR contrast and attributed to charge-state metastability. The combination of telecom-band emission, coherent spin control and compatibility with wafer-scale fabrication positions Cl-related defects in SiC as a promising platform for chip-scale quantum memories with spin-photon interfaces operating in the fiber-optic telecommunication windows.

quant-ph↗

arXiv2025

Engineering chlorine-based emitters in silicon carbide for telecom-band quantum technologies

We report the experimental realization and optical characterization of chlorine-vacancy (ClV) color centers in 4H-SiC emitting in the fiber-optic telecom bands. These defects are created via chlorine ion implantation followed by high-temperature annealing. Photoluminescence spectroscopy reveals four distinct ClV configurations with zero-phonon lines (ZPLs) located in the O-band (1260 - 1360 nm), S-band (1460 - 1530 nm) and C-band (1530 - 1565 nm). Controlled implantation and annealing experiments confirm that the ClV centers originate specifically from chlorine incorporation into SiC and are not intrinsic to this material. We optimize the creation conditions for ClV ensembles and demonstrate negligible reduction of the ZPL intensity up to a temperature of 30 K. These results establish ClV defects as a new class of telecom-band color centers in a CMOS-compatible platform, offering strong potential for scalable quantum networks.

quant-ph↗

arXiv2025

Imaging of electrical signals in a quantum SiC microscope

We report the experimental realization of a quantum silicon carbide microscope (QSiCM) and demonstrate its functionality by imaging magnetic fields generated by electrical currents. We employ a dual-frequency sensing protocol to enhance the readout contrast and suppress noise arising from strain and temperature fluctuations. This approach enables spatial imaging of current-induced magnetic fields with a field of view of $50 \times 50 $ virtual pixels, temporal resolution of $50\,\mathrm{ms}$, spatial resolution of $30\,\mathrm{μm}$ and sensitivity of about $2\,\mathrm{μT \, Hz^{-1/2}}$ per pixel. Further sensitivity enhancement is anticipated through the use of isotopically purified SiC and improved light collection in crystallographically optimized wafer orientations. In addition, we implement a microwave-free imaging protocol based on spin level anticrossing, offering simplified operation with enhanced sensitivity. The demonstrated platform is compatible with commercial, wafer-scale fabrication and holds strong potential for applications in biomedical imaging and diagnostics, as well as non-invasive current and temperature mapping in high-power electronic devices.

quant-ph↗

arXiv2024

Nuclear spin polarization in silicon carbide at room temperature in the Earth's magnetic field

Coupled electron-nuclear spins represent a promising quantum system, where the optically induced electron spin polarization can be dynamically transferred to nuclear spins via the hyperfine interaction. Most experiments on dynamic nuclear polarization (DNP) are performed at cryogenic temperatures and/or in moderate external magnetic fields, the latter approach being very sensitive to the magnetic field orientation. Here, we demonstrate that the $^{29}$Si nuclear spins in SiC can be efficiently polarized at room temperature even in the Earth's magnetic field. We exploit the asymmetric splitting of the optically detected magnetic resonance (ODMR) lines inherent to half-integer $S = 3/2$ electron spins, such that the certain transitions involving $^{29}$Si nuclei can be clearly separated and selectively addressed using radiofrequency (RF) fields. As a model system, we use the V3 silicon vacancy in 6H-SiC, which has the zero-filed splitting parameter comparable with the hyperfine interaction constant. Our theoretical model considers DNP under optical excitation in combination with RF driving and agrees very well with the experimental data. In the case of high-fidelity electron spin polarization, the proposed DNP protocol leads to ultra-deep optical cooling of nuclear spins with an effective temperature of about 50 nK. These results provide a straightforward approach for controlling the nuclear spin under ambient conditions, representing an important step toward realizing nuclear hyperpolarization for magnetic resonance imaging and long nuclear spin memory for quantum logic gates.

cond-mat.mtrl-sci↗

arXiv2024

Programmable activation of quantum emitters in high-purity silicon with focused carbon ion beams

Carbon implantation at the nanoscale is highly desired for the engineering of defect-based qubits in a variety of materials, including silicon, diamond, SiC and hBN. However, the lack of focused carbon ion beams does not allow for the full disclosure of their potential for application in quantum technologies. Here, we develop and use a carbon source for focused ion beams for the simultaneous creation of two types of quantum emitters in silicon, the W and G centers. Furthermore, we apply a multi-step implantation protocol for the programmable activation of the G centers with sub-100- nm resolution. This approach provides a route for significant enhancement of the creation yield of single G centers in carbon-free silicon wafers. Our experimental demonstration is an important step towards nanoscale engineering of telecom quantum emitters in silicon of high crystalline quality and isotope purity.

quant-ph↗

arXiv2024

Dynamical Reorientation of Spin Multipoles in Silicon Carbide by Transverse Magnetic Fields

The long-lived and optically addressable high-spin state of the negatively charged silicon vacancy ($\mathrm{V_{Si}}$) in silicon carbide makes it a promising system for applications in quantum technologies. Most studies of its spin dynamics have been performed in external magnetic fields applied along the symmetry axis. Here, we find that the application of weak magnetic fields perpendicular to the symmetry axis leads to nontrivial behavior caused by dynamical reorientation of the $\mathrm{V_{Si}}$ spin multipole under optical excitation. Particularly, we observe the inversion of the quadrupole spin polarization in the excited state and appearance of the dipole spin polarization in the ground state. The latter is much higher than thermal polarization and cannot be induced solely by optical excitation. Our theoretical calculations reproduce well all sharp features in the spin resonance spectra, and shine light on the complex dynamics of spin multipoles in these kinds of solid-state systems.

quant-ph↗

arXiv2023

Ultralong-term high-density data storage with atomic defects in SiC

There is an urgent need to increase the global data storage capacity, as current approaches lag behind the exponential growth of data generation driven by the Internet, social media and cloud technologies. In addition to increasing storage density, new solutions should provide long-term data archiving that goes far beyond traditional magnetic memory, optical disks and solid-state drives. Here, we propose a concept of energy-efficient, ultralong, high-density data archiving based on optically active atomic-size defects in a radiation resistance material, silicon carbide (SiC). The information is written in these defects by focused ion beams and read using photoluminescence or cathodoluminescence. The temperature-dependent deactivation of these defects suggests a retention time minimum over a few generations under ambient conditions. With near-infrared laser excitation, grayscale encoding and multi-layer data storage, the areal density corresponds to that of Blu-ray discs. Furthermore, we demonstrate that the areal density limitation of conventional optical data storage media due to the light diffraction can be overcome by focused electron-beam excitation.

cond-mat.mtrl-sci↗

arXiv2023

Identification of acoustically induced spin resonances of Si vacancy centers in 4H-SiC

The long-lived and optically addressable spin states of silicon vacancies ($\mathrm{V}_\mathrm{Si}$) in 4H-SiC make them promising qubits for quantum communication and sensing. These color centers can be created in both the hexagonal (V1) and in the cubic (V2) local crystallographic environments of the 4H-SiC host. While the spin of the V2 center can be efficiently manipulated by optically detected magnetic resonance at room temperature, spin control of the V1 centers above cryogenic temperatures has so far remained elusive. Here, we show that the dynamic strain of surface acoustic waves can overcome this limitation and efficiently excite magnetic resonances of V1 centers up to room temperature. Based on the width and temperature dependence of the acoustically induced spin resonances of the V1 centers, we attribute them to transitions between spin sublevels in the excited state. The acoustic spin control of both kinds of $\mathrm{V}_\mathrm{Si}$ centers in their excited states opens new ways for applications in quantum technologies based on spin-optomechanics.

quant-ph↗

arXiv2022

Unveiling the Zero-Phonon Line of the Boron Vacancy Center by Cavity Enhanced Emission

Negatively charged boron vacancies ($V_B^-$) in hexagonal boron nitride (hBN) exhibit a broad emission spectrum due to strong electron-phonon coupling and Jahn-Teller mixing of electronic states. As such, the direct measurement of zero-phonon line (ZPL) of $V_B^-$ has remained elusive. Here, we measure the room-temperature ZPL wavelength to be $773\pm2$ nm by coupling the hBN layer to the high-Q nanobeam cavity. As the wavelength of cavity mode is tuned, we observe a pronounced intensity resonance, indicating the coupling to $V_B^-$. Our observations are consistent with the spatial redistribution of $V_B^-$ emission. Spatially resolved measurements show a clear Purcell effect maximum at the midpoint of the nanobeam, in accord with the optical field distribution of the cavity mode. Our results are in good agreement with theoretical calculations, opening the way to using $V_B^-$ as cavity spin-photon interfaces.

cond-mat.mes-hall↗

arXiv2022

Wafer-scale nanofabrication of telecom single-photon emitters in silicon

A highly promising route to scale millions of qubits is to use quantum photonic integrated circuits (PICs), where deterministic photon sources, reconfigurable optical elements, and single-photon detectors are monolithically integrated on the same silicon chip. The isolation of single-photon emitters, such as the G centers and W centers, in the optical telecommunication O-band, has recently been realized in silicon. In all previous cases, however, single-photon emitters were created uncontrollably in random locations, preventing their scalability. Here, we report the controllable fabrication of single G and W centers in silicon wafers using focused ion beams (FIB) with a probability exceeding 50%. We also implement a scalable, broad-beam implantation protocol compatible with the complementary-metal-oxide-semiconductor (CMOS) technology to fabricate single telecom emitters at desired positions on the nanoscale. Our findings unlock a clear and easily exploitable pathway for industrial-scale photonic quantum processors with technology nodes below 100 nm.

quant-ph↗

arXiv2021

Inverted fine structure of a 6H-SiC qubit enabling robust spin-photon interface

Optically controllable solid-state spin qubits are one of the basic building blocks for applied quantum technology. Efficient extraction of emitted photons and a robust spin-photon interface are crucial for the realization of quantum sensing protocols and essential for the implementation of quantum repeaters. Though silicon carbide (SiC) is a very promising material platform hosting highly-coherent silicon vacancy spin qubits, a drawback for their practical application is the unfavorable ordering of the electronic levels in the optically excited state. Here, we demonstrate that due to polytypism of SiC, a particular type of silicon vacancy qubits in 6H-SiC possesses an unusual inverted fine structure. This results in the directional emission of light along the hexagonal crystallographic axis, making photon extraction more efficient and integration into photonic structures technologically straightforward. From the angular polarization dependencies of the emission, we reconstruct the spatial symmetry and determine the optical selection rules depending on the local deformation and spin-orbit interaction, enabling direct implementation of robust spin-photon entanglement schemes. Furthermore, the inverted fine structure leads to unexpected behavior of the spin readout contrast. It vanishes and recovers with lattice cooling due to two competing optical spin pumping mechanisms. Our experimental and theoretical approaches provide a deep insight into the optical and spin properties of atomic-scale qubits in SiC required for quantum communication and distributed quantum information processing.

quant-ph↗

arXiv2021

Acoustically induced coherent spin trapping

Hybrid spin-optomechanical quantum systems offer high flexibility, integrability and applicability for quantum science and technology. Particularly, on-chip surface acoustic waves (SAWs) can efficiently drive spin transitions in the ground states (GSs) of atomic-scale, color centre qubits, which are forbidden in case of the more frequently used electromagnetic fields. Here, we demonstrate that strain-induced spin interactions within their optically excited state (ES) can exceed by two orders of magnitude the ones within the GS. This gives rise to novel physical phenomena, such as the acoustically induced coherent spin trapping (CST) unvealed here. The CST manifests itself as the spin preservation along one particular direction under the coherent drive of the GS and ES by the same acoustic field. Our findings provide new opportunities for the coherent control of spin qubits with dynamically generated strain fields that can lead towards the realization of future spin-acoustic quantum devices.

quant-ph↗

arXiv2020

Stress-controlled zero-field spin splitting in silicon carbide

We report the influence of static mechanical deformation on the zero-field splitting of silicon vacancies in silicon carbide at room temperature. We use AlN/6H-SiC heterostructures deformed by growth conditions and monitor the stress distribution as a function of distance from the heterointerface with spatially-resolved confocal Raman spectroscopy. The zero-field splitting of the V1/V3 and V2 centers in 6H-SiC, measured by optically-detected magnetic resonance, reveal significant changes at the heterointerface compared to the bulk value. This approach allows unambiguous determination of the spin-deformation interaction constant, which turns out to be $0.75 \, \mathrm{GHz}$ for the V1/V3 centers and $0.5 \, \mathrm{GHz}$ for the V2 centers. Provided piezoelectricity of AlN, our results offer a strategy to realize the on-demand fine tuning of spin transition energies in SiC by deformation.

cond-mat.mtrl-sci↗

arXiv2020

Stress distribution at the AlN/SiC heterointerface probed by Raman spectroscopy

We grow AlN/4H-SiC and AlN/6H-SiC heterostructures by physical vapor deposition and characterize the heterointerface with nanoscale resolution. Furthermore, we investigate the spatial stress and strain distribution in these heterostructures using confocal Raman spectroscopy. We measure the spectral shifts of various vibrational Raman modes across the heterointerface and along the entire depth of the 4H- and 6H-SiC layers. Using the earlier experimental prediction for the phonon-deformation potential constants, we determine the stress tensor components in SiC as a function of the distance from the AlN/SiC heterointerface. In spite that the lattice parameter of SiC is smaller than that of AlN, the SiC layers are compressively strained at the heterointerface. This counterintuitive behavior is explained by different coefficients of thermal expansion of SiC and AlN when the heterostructures are cooled from growth to room temperature. The compressive stress values are maximum at the heterointerface, approaching one GPa, and relaxes to the equilibrium value on the scale of several tens of microns from the heterointerface.

cond-mat.mtrl-sci↗

arXiv2020

Mapping the stray fields of a nanomagnet using spin qubits in SiC

We report the use of optically addressable spin qubits in SiC to probe the magnetic stray fields generated by a ferromagnetic microstructure lithographically patterned on the surface of a SiC crystal. The stray fields cause shifts in the resonance frequency of the spin centers. The spin resonance is driven by a micrometer-sized microwave antenna patterned adjacent to the magnetic element. The patterning of the antenna is done to ensure that the driving microwave fields are delivered locally and more efficiently compared to conventional, millimeter-sized circuits. A clear difference in the resonance frequency of the spin centers in SiC is observed at various distances to the magnetic element, for two different magnetic states. Our results offer a wafer-scale platform to develop hybrid magnon-quantum applications by deploying local microwave fields and the stray field landscape at the micrometer lengthscale.

cond-mat.mtrl-sci↗

arXiv2020

Engineering telecom single-photon emitters in silicon for scalable quantum photonics

We create and isolate single-photon emitters with a high brightness approaching $10^5$ counts per second in commercial silicon-on-insulator (SOI) wafers. The emission occurs in the infrared spectral range with a spectrally narrow zero phonon line in the telecom O-band and shows a high photostability even after days of continuous operation. The origin of the emitters is attributed to one of the carbon-related color centers in silicon, the so-called G center, allowing purification with the $^{12}$C and $^{28}$Si isotopes. Furthermore, we envision a concept of a highly-coherent scalable quantum photonic platform, where single-photon sources, waveguides and detectors are integrated on a SOI chip. Our results provide a route towards the implementation of quantum processors, repeaters and sensors compatible with the present-day silicon technology.

physics.app-ph↗

arXiv2020

Anisotropic Spin-Acoustic Resonance in Silicon Carbide at Room Temperature

We report on acoustically driven spin resonances in atomic-scale centers in silicon carbide at room temperature. Specifically, we use a surface acoustic wave cavity to selectively address spin transitions with magnetic quantum number differences of $\pm$1 and $\pm$2 in the absence of external microwave electromagnetic fields. These spin-acoustic resonances reveal a non-trivial dependence on the static magnetic field orientation, which is attributed to the intrinsic symmetry of the acoustic fields combined with the peculiar properties of a half-integer spin system. We develop a microscopic model of the spin-acoustic interaction, which describes our experimental data without fitting parameters. Furthermore, we predict that traveling surface waves lead to a chiral spin-acoustic resonance, which changes upon magnetic field inversion. These results establish silicon carbide as a highly-promising hybrid platform for on-chip spin-optomechanical quantum control enabling engineered interactions at room temperature.

cond-mat.mes-hall↗

arXiv2020

Local vibrational modes of Si vacancy spin qubits in SiC

Silicon carbide is a very promising platform for quantum applications because of extraordinary spin and optical properties of point defects in this technologically-friendly material. These properties are strongly influenced by crystal vibrations, but the exact relationship between them and the behavior of spin qubits is not fully investigated. We uncover the local vibrational modes of the Si vacancy spin qubits in as-grown 4H-SiC. We apply the resonant microwave field to isolate the contribution from one particular type of defects, the so-called V2 center, and observe the zero-phonon line together with seven equally-separated phonon replicas. Furthermore, we present first-principles calculations of the photoluminescence lineshape, which are in excellent agreement with our experimental data. To boost up the calculation accuracy and decrease the computation time, we extract the force constants using machine learning algorithms. This allows us to identify dominant modes in the lattice vibrations coupled to an excited electron during optical emission in the Si vacancy. The resonance phonon energy of 36 meV and the Debye-Waller factor of about 6% are obtained. We establish experimentally that the activation energy of the optically-induced spin polarization is given by the local vibrational energy. Our findings give insight into the coupling of electronic states to vibrational modes in SiC spin qubits, which is essential to predict their spin, optical, mechanical and thermal properties. The approach described can be applied to a large variety of spin defects with spectrally overlapped contributions in SiC as well as in other 3D and 2D materials.

quant-ph↗