Silicon Carbide Boosts Quantum Data Storage with Millisecond-Long Spin Coherence

Scientists have demonstrated a coherent spin-photon interface using single PL6 colour centres in silicon carbide, a material gaining prominence for quantum information processing. Zhen-Xuan He, Gergő Thiering (HUN-REN Wigner Research Centre for Physics), and Rui-Jian Liang (Laboratory of Quantum Information, University of Science and Technology of China) et al. present a comprehensive spectroscopic and theoretical analysis resolving the excited-state fine structure of these centres. This research is significant because it achieves high spin initialisation fidelity and readout contrast, alongside narrow optical linewidths and extended spin coherence times through dynamical decoupling. These findings establish PL6 centres as a viable and competitive solid-state platform for spin-photon interfaces within a commercially available semiconductor material.

This research demonstrates a strong and controllable interface between electron spins and photons, paving the way for advanced quantum information processing. The work details a comprehensive investigation of single PL6 centers, combining spectroscopic analysis with theoretical modelling to fully resolve the excited-state fine structure.

Strain-dependent measurements were crucial in validating the group-theoretical model developed to understand the center’s properties. A key achievement of this study is the demonstration of exceptionally high spin initialization fidelity, reaching 99.69%. This level of accuracy is vital for reliably preparing quantum bits, or qubits, in a known state, a fundamental requirement for performing complex quantum operations.
Furthermore, researchers achieved a readout contrast of 98.31%, indicating a clear distinction between quantum states and enhancing the reliability of measurements. The spin, photon transition exhibited narrow optical linewidths of approximately 180MHz and a polarization visibility of around 82%, facilitating efficient communication of quantum information using light.

Coherent optical driving enabled Rabi frequencies up to 2.895GHz, demonstrating strong coupling between light and the electron spin. Dynamical decoupling techniques extended the spin coherence time from 0.5ms to 5.70ms, prolonging the duration for which quantum information can be stored and processed.

These results firmly establish PL6 centers as a viable solid-state spin, photon interface within a commercially available semiconductor platform. Understanding the excited-state fine structure was essential, and the team developed a theoretical model validated by strain-dependent photoluminescence excitation spectroscopy.

This breakthrough combines exceptional spin, optical performance with the inherent technological advantages of silicon carbide, offering a promising pathway towards scalable quantum networks and advanced quantum devices. The high spin polarization fidelity, substantial optical Rabi frequencies, narrow optical linewidths, and extended coherence times position PL6 centers as a strong contender in the field of quantum information science.

Strain-dependent spectroscopy and Hamiltonian parameterisation of PL6 centres in silicon carbide

Spectroscopic analysis with group-theoretical modeling initiated a comprehensive investigation of single PL6 centers in silicon carbide. To fully resolve the excited-state fine structure, strain-dependent measurements were performed on seven PL6 centers, varying transverse strain from 0.688 to 12.416GHz.

Experimental energies obtained from multi-peak Lorentzian fits closely matched theoretical eigenvalues calculated using a full Hamiltonian, validated by global Bayesian fitting which yielded values of λ = 5.739GHz [5.656, 5.881], D1 = 0.026GHz [0.0004, 0.037], D2 = 0.285GHz [0.272, 0.302], and DES = 0.932GHz [0.913, 0.957]. Spin-selective photoluminescence excitation (PLE) spectra were measured under microwave driving resonant with the ground-state zero-field splitting of 1.365GHz, enabling excitation of specific spin states.

Representative PLE spectra of a low-strain PL6 center clearly resolved transitions A1, A2, Ex, Ey, E1, and E2, demonstrating a near-degeneracy of E1 and E2 similar to NV centers and c-axis divacancies. Time-resolved PLE measurements, comprising 895 scans, confirmed spectral stability comparable to previously reported values.

Analysis of linewidths as a function of resonant laser power revealed narrow features, with A2, A1, E1, and E2 transitions remaining below 450MHz at 900nW and measuring approximately 180MHz at 100nW. Resonant optical excitation drove selective spin-flip processes, with excitation via Ex and Ey transitions flipping the spin from |ms = 0⟩ to |ms = ±1⟩, while A1, A2, or E1,2 pathways returned the spin to |ms = 0⟩.

Fluorescence decay measurements under 800nW resonant excitation via A2, A1, and E1,2 transitions revealed a prolonged decay lifetime for the A2 state, indicating a well-isolated spin-photon interface. Optimization of laser power resulted in a spin initialization fidelity of 99.69 ±0.03%, a crucial metric for high-fidelity quantum operations. Rabi oscillations, observed under a 5.7 mT field, exhibited a contrast of 98.31 ±1.03%, further demonstrating precise spin control.

High-fidelity spin control and coherence in silicon carbide PL6 centres

Researchers have demonstrated a spin initialization fidelity of 99.69% for the PL6 color center in silicon carbide, establishing a competitive platform for solid-state quantum technologies. This achievement signifies a substantial step towards reliable quantum bit preparation, crucial for performing complex quantum operations with high accuracy.

Associated with this high fidelity is a readout contrast of 98.31%, indicating a strong and discernible signal for determining the quantum state. The study details narrow optical linewidths of approximately 180MHz for the spin, photon, entangled A2 transition, alongside a polarization visibility of around 82%.

These narrow linewidths are essential for high-spectral-purity optical addressing of the quantum bit, enabling precise control and manipulation. Coherent optical driving facilitated Rabi frequencies up to 2.895GHz, demonstrating the ability to rapidly manipulate the spin state using light. Dynamical decoupling techniques extended the spin coherence time from 0.5 milliseconds to 5.70 milliseconds.

This extension of coherence is vital for maintaining quantum information over longer periods, allowing for more intricate quantum computations. The research establishes PL6 centers as a viable spin, photon interface within a commercially available semiconductor platform, leveraging the advantages of silicon carbide for scalable quantum device fabrication.

Detailed analysis of the excited-state fine structure was achieved through group-theoretical modeling and strain-dependent measurements. These measurements validated a theoretical model describing the energy levels of the PL6 center, providing a deeper understanding of its quantum properties. Strain-dependent photoluminescence excitation spectroscopy further refined the characterization of the PL6 center, confirming the accuracy of the theoretical predictions.

High Fidelity Spin Control and Coherent Optical Properties of Silicon Carbide PL6 Centres

The PL6 center in silicon carbide represents a highly competitive platform for quantum information science. Researchers have comprehensively characterized the excited-state fine structure of these centers, demonstrating exceptional performance across key metrics relevant to quantum photonic applications.

Precise determination of spin-orbit coupling and spin-spin interaction parameters provides crucial experimental data for theoretical calculations aimed at identifying the specific atomic structure of the PL6 center. Notably, the demonstrated spin initialization fidelity reaches 99.69% with a readout contrast of 98.31%, comparable to the best results achieved with divacancy centers in silicon carbide.

Narrow optical linewidths, extending to approximately 450MHz even at higher power levels, ensure high spectral purity for optical addressing. Furthermore, coherent optical driving enables rapid quantum operations with Rabi frequencies up to 2.895GHz, and dynamical decoupling extends spin coherence times from approximately 0.5 milliseconds to 5.70 milliseconds.

The identification of an intrinsic spin, photon entangled state within the |A2⟩ excited state, confirmed by symmetric optical decay dynamics and high spin-dependent polarization visibility, offers a direct pathway for deterministic generation of entanglement in solid-state systems. While coherence times remain competitive despite the use of commercial-grade silicon carbide containing residual paramagnetic impurities, isotopically purified materials could further enhance performance. This combination of outstanding spin-optical properties, long coherence times, and compatibility with established semiconductor technology offers a compelling route towards practical quantum information processing.