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arXiv:2203.08177 · Physical Review Applied

Spin-Optical Dynamics and Quantum Efficiency of a Single V1 Center in Silicon Carbide

Naoya Morioka, Di Liu, Öney O. Soykal, Izel Gediz, Charles Babin, Rainer Stöhr, Takeshi Ohshima, Nguyên Tiên Són, Jawad Ul‐Hassan, Florian Kaiser, Jörg Wrachtrup

Published May 3, 2022• 19 citations

Abstract

Color centers in silicon carbide are emerging candidates for distributed spin-based quantum applications due to the scalability of host materials and the demonstration of integration into nanophotonic resonators. Recently, silicon vacancy centers in silicon carbide have been identified as a promising system with excellent spin and optical properties. Here, we fully study the spin-optical dynamics of the single silicon vacancy center at hexagonal lattice sites, namely V1, in 4H-polytype silicon carbide. By utilizing resonant and above-resonant sublifetime pulsed excitation, we determine spin-dependent excited-state lifetimes and intersystem-crossing rates. Our approach to inferring the intersystem-crossing rates is based on all-optical pulsed initialization and readout scheme, and is applicable to spin-active color centers with similar dynamics models. In addition, the optical transition dipole strength and the quantum efficiency of V1 defect are evaluated based on coherent optical Rabi measurement and local-field calibration employing electric field simulation. The measured rates well explain the results of spin-state polarization dynamics, and we further discuss the altered photoemission dynamics in resonant enhancement structures such as radiative lifetime shortening and Purcell enhancement. By providing a thorough description of the V1 center's spin-optical dynamics, our work provides deep understanding of the system, which guides implementations of scalable quantum applications based on silicon vacancy centers in silicon carbide.

DOI: 10.1103/physrevapplied.17.054005

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Color centers in silicon carbide are emerging candidates for distributed spin-based quantum applications due to the scalability of host materials and the demonstration of integration into nanophotonic resonators. Recently, silicon vacancy centers in silicon carbide have been identified as a promising system with excellent spin and optical properties. Here, we fully study the spin-optical dynamics of the single silicon vacancy center at hexagonal lattice sites, namely V1, in 4H-polytype silicon carbide. By utilizing resonant and above-resonant sublifetime pulsed excitation, we determine spin-dependent excited-state lifetimes and intersystem-crossing rates. Our approach to inferring the intersystem-crossing rates is based on all-optical pulsed initialization and readout scheme, and is applicable to spin-active color centers with similar dynamics models. In addition, the optical transition dipole strength and the quantum efficiency of V1 defect are evaluated based on coherent optical Rabi measurement and local-field calibration employing electric field simulation. The measured rates well explain the results of spin-state polarization dynamics, and we further discuss the altered photoemission dynamics in resonant enhancement structures such as radiative lifetime shortening and Purcell enhancement. By providing a thorough description of the V1 center's spin-optical dynamics, our work provides deep understanding of the system, which guides implementations of scalable quantum applications based on silicon vacancy centers in silicon carbide.

Abstract The negatively charged silicon vacancy center (

{{\rm{V}}}_{{\rm{Si}}}^{-}

V Si − ) in silicon carbide (SiC) is an emerging color center for quantum technology covering quantum sensing, communication, and computing. Yet, limited information currently available on the internal spin-optical dynamics of these color centers prevents us from achieving the optimal operation conditions and reaching the maximum performance especially when integrated within quantum photonics. Here, we establish all the relevant intrinsic spin dynamics of the

{{\rm{V}}}_{{\rm{Si}}}^{-}

V Si − center at cubic lattice site (V2) in 4H-SiC by an in-depth electronic fine structure modeling including the intersystem-crossing and deshelving mechanisms. With carefully designed spin-dependent measurements, we obtain all the previously unknown spin-selective radiative and non-radiative decay rates. To showcase the relevance of our work for integrated quantum photonics, we use the obtained rates to propose a realistic implementation of time-bin entangled multi-photon GHZ and cluster state generation. We find that up to three-photon GHZ or cluster states are readily within reach using the existing nanophotonic cavity technology.

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

{{\rm{V}}}_{{\rm{Si}}}^{-}

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

A_2

~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.

The negatively-charged silicon vacancy center (

\rm V_{Si}^-

) in silicon carbide (SiC) is an emerging color center for quantum technology covering quantum sensing, communication, and computing. Yet, limited information currently available on the internal spin-optical dynamics of these color centers prevents us achieving the optimal operation conditions and reaching the maximum performance especially when integrated within quantum photonics. Here, we establish all the relevant intrinsic spin dynamics of negatively charged

0.5

center in 4H-SiC by an in-depth electronic fine structure modeling including intersystem-crossing and deshelving mechanisms. With carefully designed spin-dependent measurements, we obtain all previously unknown spin-selective radiative and non-radiative decay rates. To showcase the relevance of our work for integrated quantum photonics, we use the obtained rates to propose a realistic implementation of time-bin entangled multi-photon GHZ and cluster state generation. We find that up to 3-photon GHZ/cluster states are readily within reach using the existing nanophotonic cavity technology.

Silicon carbide has recently been developed as a platform for optically addressable spin defects. In particular, the neutral divacancy in the 4H polytype displays an optically addressable spin-1 ground state and near-infrared optical emission. Here, we present the Purcell enhancement of a single neutral divacancy coupled to a photonic crystal cavity. We utilize a combination of nanolithographic techniques and a dopant-selective photoelectrochemical etch to produce suspended cavities with quality factors exceeding 5000. Subsequent coupling to a single divacancy leads to a Purcell factor of ∼50, which manifests as increased photoluminescence into the zero-phonon line and a shortened excited-state lifetime. Additionally, we measure coherent control of the divacancy ground-state spin inside the cavity nanostructure and demonstrate extended coherence through dynamical decoupling. This spin-cavity system represents an advance toward scalable long-distance entanglement protocols using silicon carbide that require the interference of indistinguishable photons from spatially separated single qubits.

Silicon vacancy (VSi) centers in 4H silicon carbide have emerged as a highly promising platform for semiconductor-based quantum technologies, combining excellent spin and optical properties with an industrial-grade, CMOS-compatible material. As these defects are increasingly integrated into practical quantum devices, they inevitably encounter lattice strain. However, while the impact of strain is well documented for other solid-state defects like NV centers in diamond, its specific influence on key VSi spin dynamics such as initialization fidelity and state lifetimes remain largely unexplored. In this work, we address this critical gap by designing fully optical pulse sequences and incorporating the effective spin-3/2 strain Hamiltonian into our analysis. This combined approach allows us to isolate both axial and transverse strain contributions and systematically characterize their effect on the metastable state transition rates. Specifically, we reveal that strain significantly reduces the transition rates from the energetically lowest metastable state to the ground state quartet, leading to decreased photon emission. Supported by first-principles calculations, our findings provide a deeper understanding of VSi spin-strain dynamics, yielding crucial insights for the robust deployment of these centers in realistic, strain-prone environments.

Divacancy defects in silicon carbide have long-lived electronic spin states and sharp optical transitions. Because of the various polytypes of SiC, hundreds of unique divacancies exist, many with spin properties comparable to the nitrogen-vacancy center in diamond. If ensembles of such spins can be all-optically manipulated, they make compelling candidate systems for quantum-enhanced memory, communication, and sensing applications. We report here direct all-optical addressing of basal plane-oriented divacancy spins in 4H-SiC. By means of magneto-spectroscopy, we fully identify the spin triplet structure of both the ground and the excited state, and use this for tuning of transition dipole moments between particular spin levels. We also identify a role for relaxation via intersystem crossing. Building on these results, we demonstrate coherent population trapping -a key effect for quantum state transfer between spins and photons- for divacancy sub-ensembles along particular crystal axes. These results, combined with the flexibility of SiC polytypes and device processing, put SiC at the forefront of quantum information science in the solid state.