Coherent Spin-Photon Interface of single PL6 Color Centers in Silicon Carbide

Abstract

The PL6 color center in silicon carbide has recently emerged as a promising platform for quantum information processing, yet its coherent spin--photon interface has remained largely unexplored. Here we present a comprehensive investigation of single PL6 centers, combining spectroscopy with theoretical analysis. The excited-state fine structure is fully resolved using group-theoretical modeling and strain-dependent measurements. Under resonant excitation, we achieve a spin initialization fidelity of $99.69 \pm 0.03\%$ and a readout contrast of $98.31 \pm 1.03\%$. The spin--photon--entangled $A_2$ transition exhibits narrow optical linewidths ($\sim 180$~MHz) and a polarization visibility of $\sim 82\%$. Coherent optical driving enables Rabi frequencies up to $2.895$~GHz, while dynamical decoupling extends the spin coherence time from $0.5$~ms to $5.70$~ms. Our results establish PL6 as a competitive solid-state spin--photon interface hosted in a commercially available semiconductor platform.

Figures (4)

• Figure 1: Low-temperature fine structure of the PL6 color center. (a) Energy-level diagram of the $^{3}\mathrm{E}$ excited state, showing splittings from spin-orbit coupling $\lambda$ and spin-spin interactions ($D_{\mathrm{ES}}$, $D_1$, $D_2$). (b) Spin-selective resonant excitation under microwave driving at $D_{\mathrm{GS}} = 1.365\ \mathrm{GHz}$. (c) Strain-dependent evolution of excited-state levels with transverse strain $\delta_{\perp}$. Solid curves: theoretical model; dots: experimental data from seven PL6 centers. Blue arrow indicates data from (d). (d) PLE spectrum of a low-strain PL6 center ($\delta_{\perp} = 0.688\ \mathrm{GHz}$) with multi-peak Lorentzian fit (red). (e) Time-resolved PLE measurement over 895 cycles, showing spectral stability. (f) Linewidth versus resonant laser power for transitions $A_2$, $A_1$, $E_x$, $E_y$, and $E_{1,2}$. Error bars indicate fitting uncertainties.
• Figure 2: High-fidelity spin control and readout via resonant excitation. (a) Schematic of spin-flip processes under resonant optical excitation. (b) Fluorescence decay under $800\ \mathrm{nW}$ resonant excitation via $A_2$, $A_1$, and $E_{1,2}$ transitions. $A_2$ shows prolonged decay lifetime. Solid lines: bi-exponential fits. (c) Spin polarization fidelity vs. $E_{1,2}$ laser power, reaching $99.69 \pm 0.03\%$ at optimum power. (d) Spin-flip rates on $E_x$ and $E_y$ transitions for three PL6 centers with different strains. Error bars indicate fitting uncertainties. (e) Upper: Pulse sequence using $914\ \mathrm{nm}$ initialization, $E_{1,2}$ polarization, and $E_y$ readout. Lower: Single-spin Rabi oscillations under $5.7\ \mathrm{mT}$ field, showing $98.31 \pm 1.03\%$ contrast.
• Figure 3: Optical Rabi oscillation and coherent control of a single PL6 color center. (a) Spin-selective and polarization-dependent optical transitions, showing $\lvert m_s = \pm1 \rangle \leftrightarrow \lvert A_2 \rangle$ and $\lvert m_s = 0 \rangle \leftrightarrow \lvert E_{x(y)} \rangle$ pathways. (b) Rabi oscillations for $\lvert m_s = 0 \rangle \leftrightarrow \lvert E_x \rangle$ at 23.8 $\mu$W (black), 37.5 $\mu$W (red), and 60 $\mu$W (blue). (c) Rabi oscillations for $\lvert m_s = \pm1 \rangle \leftrightarrow \lvert A_2 \rangle$ at 56 $\mu$W. Solid curves: numerical solutions from master equations. (d) Rabi frequency $\Omega$ as a function of $\sqrt{P}$ for $\lvert m_s = 0 \rangle \leftrightarrow \lvert E_{x(y)} \rangle$ (top) and $\lvert m_s = \pm1 \rangle \leftrightarrow \lvert A_2 \rangle$ (bottom), showing linear scaling. Data from Supplementary Notes 6 and 7. (e) Polarization visibility of $\lvert m_s = \pm1 \rangle \rightarrow \lvert A_2 \rangle$ transition. Points: photon counts during $\pi$-pulses at different QWP angles over $\sim 10^9$ repetitions. Solid curves: cosine fits yielding $\sim$ 82% visibility.
• Figure 4: Decoherence time under dynamical decoupling. (a-b) Hahn-echo measurements at $B \approx 5.7\ \mathrm{mT}$ and $17.1\ \mathrm{mT}$. (c) $T_2$ decay curves under XY8 sequences with increasing $\pi$-pulse number $N = 2, 4, 8, 16$ at $B \approx 17.1\ \mathrm{mT}$, fitted to stretched exponential. (d) Coherence time $T_2(N)$ vs. pulse number $N$ at both fields, following power-law scaling. All data at 6.35 K.