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Physical review. B./Physical review. B

Nitrogen vacancy center in cubic silicon carbide: A promising qubit in the 1.5μm spectral range for photonic quantum networks

Soroush Abbasi Zargaleh, Sophie Hameau, B. Eblé, Florent Margaillan, Hans Jürgen von Bardeleben, J. L. Cantin, Weibo Gao

Published Oct 15, 2018• 53 citations
Publisher

Abstract

We have investigated the optical properties of the ${(\mathrm{NV})}^{\ensuremath{-}}$ center in 3C-SiC to determine the photoluminscence zero phonon line (ZPL) associated with the $^{3}\mathrm{E}\ensuremath{\rightarrow}^{3}\mathrm{A}_{2}$ intracenter transition. Combining electron paramagnetic resonance and photoluminescence spectroscopy, we show that the ${\mathrm{NV}}^{\ensuremath{-}}\phantom{\rule{0.28em}{0ex}}\mathrm{center}$ in 3C-SiC has a ZPL line at 1.468 $\ensuremath{\mu}\mathrm{m}$ in excellent agreement with theoretical predictions. The ZPL line can be observed up to $T=100$ K. The negatively charged NV center in 3C-SiC is the structural isomorphe of the NV center in diamond and has equally a spin $S=1$ ground state and a spin $S=1$ excited state, long spin lattice relaxation times and presents optically induced groudstate spin polarization. These properties make it already a strong competitor to the NV center in diamond, but as its optical domain is shifted in the near infrared at $1.5\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$, the NV center in 3C-SiC is compatible with quantum photonic networks and silicon based microelectronics.

DOI
10.1103/physrevb.98.165203

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We have investigated the optical properties of the (NV)\ensuremath−{(\mathrm{NV})}^{\ensuremath{-}}(NV)\ensuremath− center in 3C-SiC to determine the photoluminscence zero phonon line (ZPL) associated with the 3E\ensuremath→3A2^{3}\mathrm{E}\ensuremath{\rightarrow}^{3}\mathrm{A}_{2}3E\ensuremath→3A2​ intracenter transition. Combining electron paramagnetic resonance and photoluminescence spectroscopy, we show that the NV\ensuremath−center{\mathrm{NV}}^{\ensuremath{-}}\phantom{\rule{0.28em}{0ex}}\mathrm{center}NV\ensuremath−center in 3C-SiC has a ZPL line at 1.468 \ensuremathμm\ensuremath{\mu}\mathrm{m}\ensuremathμm in excellent agreement with theoretical predictions. The ZPL line can be observed up to T=100T=100T=100 K. The negatively charged NV center in 3C-SiC is the structural isomorphe of the NV center in diamond and has equally a spin S=1S=1S=1 ground state and a spin S=1S=1S=1 excited state, long spin lattice relaxation times and presents optically induced groudstate spin polarization. These properties make it already a strong competitor to the NV center in diamond, but as its optical domain is shifted in the near infrared at 1.5\ensuremathμm1.5\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}1.5\ensuremathμm, the NV center in 3C-SiC is compatible with quantum photonic networks and silicon based microelectronics.
Robust single spin color centers in solid state systems with telecom wavelength emission are vital to quantum photonics and quantum networks. The nitrogen vacancy (NV) centers in silicon carbide (SiC) have become promising platforms for those applications. However, little is known about the detailed optical properties of the NV centers. In this paper, we investigate the photophysics of the single NV centers in 4H-SiC. The results demonstrate that the NV centers comprise three energy-level electronic structures. Particularly, for c -axis NV centers, both the excitation and the emission polarization degrees are larger than 90%. Photon purity and photostability of the single NV centers are maintained at an elevated temperature up to 400 K. These experiments constitute an important step toward using the NV centers in SiC with respect to quantum photonics.
Defect based qubit systems like the nitrogen vacancy center in diamond have recently emerged as promising candidates for quantum technologies due to their combination of long coherence times, room temperature operation, and robust optical interface. In order to realize many of their proposed applications, defect qubits must be incorporated into scalable devices architectures consisting of photonic, mechanical, or electrical degrees of freedom. Despite much recent progress, many challenges remain for diamond growth and device fabrication. As an alternate approach, we engaged in a search for nitrogen vacancy center analogues in alternative materials with the hope of obtaining a greater degree of control over defect and material properties. Ultimately, we discovered that divacancy-related point defects in all three of the most common forms of silicon carbide- termed 4H, 6H, and 3C- act as analogues to the nitrogen vacancy center in diamond. We chose to focus our research primarily on defects in 3C silicon carbide (termed 'Ky5' defects) because of its availability as a single crystal heteroepitaxial thin film grown on silicon, an advantage that greatly facilitates the fabrication of functional devices. We characterized the spin and optical properties of Ky5 defects in thin film geometries and observed many similarities to the nitrogen vacancy center. We performed the first measurements of spin dynamics in 3C silicon carbide and demonstrate coherent control of defect spins up to room temperature and observe coherence times of up to 22 microseconds. To demonstrate their use in real devices, we designed, fabricated, and characterized photonic crystal cavities in 3C silicon carbide thin films with mode volumes of less than (lambda/n)^3 and Q's as high as 1,500 with integrated Ky5 defects. Additionally, we performed simulations and analysis of the fabricated structures using observed structural imperfections to determine that the Q's are likely limited primarily by the non-vertical structure sidewall angle. Despite the modest Q's of these structures, they can be utilized to generate large local field intensities to enhance optical interactions with Ky5 qubit states within the cavities. We accomplish this by performing cavity enhanced photoluminescence excitation spectroscopy on cavity modes tuned to the zero phonon line of the defects and observe large (as high as 30 times) increases in the luminescence and optically detected magnetic resonance signals originating from the defect states and approximately 2x faster rates of ground state spin initialization. In addition, we use these techniques to probe the photoluminescence dynamics of the Ky5 defects' optical pumping cycle, perform excitation wavelength dependent studies of spin and spectral inhomogeneity, and use the small mode volume and narrowband photoluminescence enhancements of the cavities to observe spectrally distinct subensembles of defects with linewidths as narrow as 25 GHz within the inhomogeneously broadened zero phonon line. Although much is still unknown regarding the properties of these defects, they show great promise as a candidate system for defect qubit based quantum devices and technologies.
Nitrogen-vacancy (NV) centers in single-crystal CVD diamond are promising candidates for quantum sensing due to their remarkable optical and spin properties [1]. These defects exhibit stable photoluminescence (PL), long spin coherence times, and high sensitivity to external fields [2]. In this study, we present a room-temperature PL characterization of NV centers excited with a 532 nm laser. The setup was optimized for high signal-to-noise ratio and spectral resolution. Key parameters analyzed include emission intensity, zero-phonon line (ZPL) at ~637 nm, phonon sidebands, and the charge state distribution between NV⁰ and NV⁻. The NV⁻ state, crucial for spin-based sensing, is evaluated to understand its stability under different nitrogen doping conditions [3]. The relative intensities of NV⁰ and NV⁻ provide insights into nitrogen incorporation and vacancy formation. These results contribute to optimizing synthesis conditions for enhanced NV⁻ concentration, supporting the advancement of diamond-based quantum sensing technologies.
Solid-state spin defects in semiconductor matrices have become a robust medium for holding electron qubit ensembles. In this paper, the features of NV centers’ spin polarization in a silicon carbide 6 H -SiC crystal, and the laser excitation influence on the coherent properties of the color center were studied by the photoinduced pulsed EPR spectroscopy (W-band, 94 GHz). After the optical pulse, in the dark-mode regime, the characteristic time of the spin-phonon interaction of NV defects with the local environment lengthens by 1 order of magnitude compared to continuous laser irradiation, reaching a value of T 1 = 0.74 s at temperature of 50 K. An extremely efficient spin polarization (> 90%) of NV centers was discovered, which is necessary for establishing the initial pure quantum state. The obtained spin-optical and coherent properties delineate the time domain of multipulse quantum manipulations involving optical and microwave sources for promising NV centers in quantum photonics.
Photoluminescence (PL) spectra of single silicon vacancy (SiV) centers in diamond frequently feature very narrow room temperature PL lines in the near-infrared (NIR) spectral region, mostly between 820 nm and 840 nm, in addition to the well known zero-phonon line (ZPL) at approximately 738 nm [E. Neu et al., Phys. Rev. B 84, 205211 (2011)]. We here exemplarily prove for a single SiV center that this NIR PL is due to an additional purely electronic transition (ZPL). For the NIR line at 822.7 nm, we find a room temperature linewidth of 1.4 nm (2.6 meV). The line saturates at similar excitation power as the ZPL. The ZPL and NIR line exhibit identical polarization properties. Cross-correlation measurements between the ZPL and the NIR line reveal anticorrelated emission and prove that the lines originate from a single SiV center, furthermore indicating a fast switching between the transitions (0.7 ns). g(2){g}^{(2)}g(2) autocorrelation measurements exclude that the NIR line is a vibronic sideband or that it arises due to a transition from/to a metastable (shelving) state.
Silicon carbide (SiC) is a promising platform for scalable quantum technologies owing to its well-established, wafer-scale industrial processing. SiC also hosts a variety of optically active color centres including the nitrogen vacancy defect that has a spin-triplet ground state. However, strong phonon coupling in the infrared range limits photon extraction from these defects. Here, we use nanophotonic structures, specifically micro-pillar and micro-disk resonators, to enhance optical collection and spin-readout. The micro-pillar geometry yields a 4-fold increase in photon collection, accompanied by a 2.4-fold reduction in spectral noise in optically detected magnetic resonance measurements. Consequently, the magnetic field sensitivity is improved by 24%. The large mode volume of the micro-disk supports resonances spanning 1150-1250 nm, enabling broadband coupling to nitrogen vacancy emission lines. Our results demonstrate that fabrication of scalable photonic structures efficiently improves performance of silicon carbide color centers for integrated quantum light generation and sensing.