arXiv subjects

A. N. Anisimov

Publications and source records attributed to A. N. Anisimov.

11 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↗

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↗

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

Electron nuclear interactions and electronic structure of spin 3/2 color centers in silicon carbide: A high-field pulse EPR and ENDOR study

High-frequency pulse electron paramagnetic resonance (EPR) and electron nuclear double resonance (ENDOR) were used to clarify the electronic structure of the color centers with an optically induced high-temperature spin-3/2 alignment in hexagonal 4H-, 6H- and rhombic 15R- silicon carbide (SiC) polytypes. The identification is based on resolved ligand hyperfine interactions with carbon and silicon nearest, next nearest and the more distant neighbors and on the determination of the spin state. The ground state and the excited state were demonstrated to have spin S = 3/2. The microscopic model suggested from the EPR and ENDOR results is as follows: a paramagnetic negatively charged silicon vacancy that is noncovalently bonded to a non-paramagnetic neutral carbon vacancy, located on the adjacent site along the SiC symmetry c-axis.

cond-mat.mtrl-sci↗

arXiv2018

Excitation and coherent control of spin qudit modes with sub-MHz spectral resolution

Quantum bit or qubit is a two-level system, which builds the foundation for quantum computation, simulation, communication and sensing. Quantum states of higher dimension, i.e., qutrits (D = 3) and especially qudits (D = 4 or higher), offer significant advantages. Particularly, they can provide noise-resistant quantum cryptography, simplify quantum logic and improve quantum metrology. Flying and solid-state qudits have been implemented on the basis of photonic chips and superconducting circuits, respectively. However, there is still a lack of room-temperature qudits with long coherence time and high spectral resolution. The silicon vacancy centers in silicon carbide (SiC) with spin S = 3/2 are quite promising in this respect, but until now they were treated as a canonical qubit system. Here, we apply a two-frequency protocol to excite and image multiple qudit modes in a SiC spin ensemble under ambient conditions. Strikingly, their spectral width is about one order of magnitude narrower than the inhomogeneous broadening of the corresponding spin resonance. By applying Ramsey interferometry to these spin qudits, we achieve a spectral selectivity of 600 kHz and a spectral resolution of 30 kHz. As a practical consequence, we demonstrate absolute DC magnetometry insensitive to thermal noise and strain fluctuations.

quant-ph↗

arXiv2016

Optical thermometry based on level anticrossing in silicon carbide

We report a giant thermal shift of $2.1 \,$MHz/K related to the excited-state zero-field splitting in the silicon vacancy centers in 4H silicon carbide. It is obtained from the indirect observation of the optically detected magnetic resonance in the excited state using the ground state as an ancilla. Alternatively, relative variations of the zero-field splitting for small temperature differences can be detected without application of radiofrequency fields, by simply monitoring the photoluminescence intensity in the vicinity of the level anticrossing. This effect results in an all-optical thermometry technique with temperature sensitivity of $100 \,$mK/Hz$^{1/2}$ for a detection volume of approximately $10^{-6} \,$mm$^{3}$. In contrast, the zero-field splitting in the ground state does not reveal detectable temperature shift. Using these properties, an integrated magnetic field and temperature sensor can be implemented on the same center.

cond-mat.mtrl-sci↗

arXiv2016

All-optical dc nanotesla magnetometry using silicon vacancy fine structure in isotopically purified silicon carbide

We uncover the fine structure of a silicon vacancy in isotopically purified silicon carbide (4H-$^{28}$SiC) and find extra terms in the spin Hamiltonian, originated from the trigonal pyramidal symmetry of this spin-3/2 color center. These terms give rise to additional spin transitions, which are otherwise forbidden, and lead to a level anticrossing in an external magnetic field. We observe a sharp variation of the photoluminescence intensity in the vicinity of this level anticrossing, which can be used for a purely all-optical sensing of the magnetic field. We achieve dc magnetic field sensitivity of 87 nT Hz$^{-1/2}$ within a volume of $3 \times 10^{-7}$ mm$^{3}$ at room temperature and demonstrate that this contactless method is robust at high temperatures up to at least 500 K. As our approach does not require application of radiofrequency fields, it is scalable to much larger volumes. For an optimized light-trapping waveguide of 3 mm$^{3}$ the projection noise limit is below 100 fT Hz$^{-1/2}$.

cond-mat.mtrl-sci↗