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arXiv:2201.11472 · Physical Review Applied

Spectral Broadening of a Single Er3+ Ion in a Si Nanotransistor

Jiliang Yang, Jian Wang, Wenda Fan, Yangbo Zhang, Chang‐Kui Duan, Guangchong Hu, Gabriele G. de Boo, Brett C. Johnson, Jeffrey Colin McCallum, Sven M. J. Rogge, Chunming Yin, Jiangfeng Du

Published Sep 8, 2022• 7 citations
arXivHTMLPDF

Abstract

Single rare-earth ions in solids show great potential for quantum applications, including single-photon emission, quantum computing, and high-precision sensing. However, the linewidths of single rare-earth ions are often broadened due to perturbations associated with the detection methods. Identifying the dominant broadening sources is key to reduce the linewidths for practical applications. We report a spectral broadening study on a single ${\mathrm{Er}}^{3+}$ ion in a $\mathrm{Si}$ nanotransistor. The single ion spectra display a Lorentzian lineshape at all light intensities considered. The linewidth remains nearly constant at 32\ifmmode\pm\else\textpm\fi{}2 MHz in the low-intensity regime, and shows a monotonic increase with the intensity in the high-intensity regime. The power broadening does not persist over the microsecond time scales considered after resonant excitation. Nor does it depend on the resonant excitation intensity or the Zeeman shift. These observations and temperature-dependent measurements suggest that charge fluctuations are likely to be a dominant broadening source. Laser heating may also contribute to the power broadening. Charge suppression in the ${\mathrm{Er}}^{3+}$-doped region and coupling ${\mathrm{Er}}^{3+}$ ions to a confined optical mode could be implemented to reduce the spectral linewidth and to enhance the sensing precision of single ${\mathrm{Er}}^{3+}$ ions in $\mathrm{Si}$.

DOI
10.1103/physrevapplied.18.034018

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•Jan 1, 2018•10 citations
Single rare-earth ions in solids show great potential for quantum applications, including single-photon emission, quantum computing, and high-precision sensing. However, the linewidths of single rare-earth ions are often broadened due to perturbations associated with the detection methods. Identifying the dominant broadening sources is key to reduce the linewidths for practical applications. We report a spectral broadening study on a single Er3+{\mathrm{Er}}^{3+}Er3+ ion in a Si\mathrm{Si}Si nanotransistor. The single ion spectra display a Lorentzian lineshape at all light intensities considered. The linewidth remains nearly constant at 32\ifmmode\pm\else\textpm\fi{}2 MHz in the low-intensity regime, and shows a monotonic increase with the intensity in the high-intensity regime. The power broadening does not persist over the microsecond time scales considered after resonant excitation. Nor does it depend on the resonant excitation intensity or the Zeeman shift. These observations and temperature-dependent measurements suggest that charge fluctuations are likely to be a dominant broadening source. Laser heating may also contribute to the power broadening. Charge suppression in the Er3+{\mathrm{Er}}^{3+}Er3+-doped region and coupling Er3+{\mathrm{Er}}^{3+}Er3+ ions to a confined optical mode could be implemented to reduce the spectral linewidth and to enhance the sensing precision of single Er3+{\mathrm{Er}}^{3+}Er3+ ions in Si\mathrm{Si}Si.
Rare-earth ions in solid-state hosts exhibit low homogeneous broadening and long spin coherence at cryogenic temperatures thus making them a promising candidate for optical quantum memories [1], optical-microwave transducers [2] and single dopant-based devices such as single photon emitters operating at the telecommunication wavelengths [3]. Here, we present an overview of the spin and optical properties of Er ensembles in Si accessed via resonant photoluminescence excitation (PLE) spectroscopy [4]. Samples were positioned directly on top of tailor-fabricated superconducting single photon detectors, placed in a dilution refrigerator unit and resonantly excited using fiber optics. Our method provided high collection efficiency and allowed spectral measurements of low Er density samples. The observed Er PLE spectra were strongly affected by the presence of co-dopants such as O, B or P reflecting their influence on the formation of optically active Er sites and corresponding Er optical transition energies. Higher O densities resulted in especially rich PLE spectra suggesting that a variety of Er-O complexes formed due to O doping. Lowering the O concentration, we achieved PLE spectra dominated by a single Er site in P doped samples. Interestingly, the Er spin relaxation and optical coherence properties were barely affected by the employed co-dopants and mainly depended on the Er concentration. By lowering the Er concentration from relatively high (1018cm-3) to low densities (1016cm-3), we were able to increase Er spin lifetimes from ~0.1 s to ~30 s. Long spin relaxation times allowed us to identify PLE spectra of new Er sites in Si. In both concentration regimes, we observed sub-MHz transient spectral holes suggesting long optical coherence times. Furthermore, we observed sub-MHz spin transitions in both natural and isotopically purified Si and achieved spin coherence times above 1 ms in isotopically purified Si. Narrow optical linewidths and long transverse and longitudinal spin relaxation times show that Er in Si is an excellent candidate for future quantum information and communication applications.
Rare Earth (RE) ion doped nanomaterials are promising candidates for a range of quantum technology applications. Among RE ions, the so-called Kramers' ions possess spin transitions in the GHz range at low magnetic fields, which allows for high-bandwidth multimode quantum storage, fast qubit operations as well as interfacing with superconducting circuits. They also present relevant optical transitions in the infrared. In particular, Er3+{\mathrm{Er}}^{3+}Er3+ has an optical transition in the telecom band, while Nd3+{\mathrm{Nd}}^{3+}Nd3+ presents a high-emission-rate transition close to 890 nm. In this paper, we measure spectroscopic properties that are of relevance to using these materials in quantum technology applications. We find the inhomogeneous linewidth to be 10.7 GHz for Er3+{\mathrm{Er}}^{3+}Er3+ and 8.2 GHz for Nd3+{\mathrm{Nd}}^{3+}Nd3+, and the excited state lifetime T1{T}_{1}T1​ to be 13.68 ms for Er3+{\mathrm{Er}}^{3+}Er3+ and $540\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{s}$ for Nd3+{\mathrm{Nd}}^{3+}Nd3+. We study the dependence of homogeneous linewidth on temperature for both samples, with the narrowest linewidth being 379 kHz (T2=839{T}_{2}=839T2​=839 ns) for Er3+{\mathrm{Er}}^{3+}Er3+ measured at 3 K, and 62 kHz (${T}_{2}=5.14\phantom{\rule{4pt}{0ex}}\textmu{}\mathrm{s}$) for Nd3+{\mathrm{Nd}}^{3+}Nd3+ measured at 1.6 K. Further, we investigate time-dependent homogeneous linewidth broadening due to spectral diffusion and the dependence of the homogeneous linewidth on magnetic field to get additional clarity of mechanisms that can influence the coherence time. In light of our results, we discuss two applications: single qubit-state readout and a Fourier-limited single photon source.
We identify the physical mechanisms responsible for the optical homogeneous broadening in Eu 3+:Y 2 O 3 nanoparticles to determine whether rare-earth crystals can be miniaturized to volumes less than λ 3 while preserving their appeal for quantum technology hardware. By studying how the homogeneous line width depends on temperature, applied magnetic field, and measurement time scale, the dominant broadening interactions for various temperature ranges above 3 K were characterized. Below 3 K the homogeneous line width is dominated by an interaction not observed in bulk crystal studies. These measurements demonstrate that broadening due to size-dependent phonon interactions is not a significant contributor to the homogeneous line width, which contrasts previous studies in rare-earth ion nanocrystals. Importantly, the results provide strong evidence that for the 400 nm diameter nanoparticles under study the minimum line width achieved (45 ± 1 kHz at 1.3 K) is not fundamentally limited. In addition, we highlight that the expected broadening caused by electric field fluctuations arising from surface charges is comparable to the observed broadening. Under the assumption that such Stark broadening is a significant contribution to the homogeneous line width, several strategies for reducing this line width to below 10 kHz are discussed. Furthermore, it is demonstrated that the Eu 3+ hyperfine state lifetime is sufficiently long to preserve spectral features for time scales up to 1 s. These results allow integrated rare-earth ion quantum optics to be pursued at a submicron scale and, hence, open up directions for greater scaling of rare-earth quantum technology.
Rare-earth ions (REIs) have incomplete 4f shells and possess narrow optical intra-4f transitions due to shielding from electrons in the 5s and 5p orbitals, making them good candidates for solid-state optical quantum memory. The emission of Er3+ in the telecom C-band (1530 nm–1565 nm) makes it especially attractive for this application. In order to build practical, scalable devices, the REI needs to be embedded in a non-interacting host material, preferably one that can be integrated with silicon. In this paper, we show that Er3+ can be isovalently incorporated into epitaxial Y2O3 thin films on Si (111). We report on the synthesis of epitaxial, single-crystalline Er:Y2O3 on Si with a narrow inhomogeneous linewidth in the photoluminescence (PL) spectra, 5.1 GHz (<100 mK), and an optical excited state lifetime of 8.1 ms. The choice of Y2O3 was driven by its low nuclear spin and small lattice mismatch with Si. Using PL and electron paramagnetic resonance, we show that Er3+ substitutes for Y in the crystal lattice. The role of interfacial SiOx, diffusion of silicon into the film, and the effect of buffer layers on the inhomogeneous PL linewidth are examined. We also find that the linewidth decreased monotonically with film thickness but surprisingly exhibits no correlation with the film crystalline quality, as measured by the x-ray rocking curve scans, suggesting other factors at play that limit the inhomogeneous broadening in Y2O3 films.
The implementation of scalable quantum networks requires photons at the telecom band and long-lived spin coherence. The single Er3+ in solid-state hosts is an important candidate that fulfills these critical requirements simultaneously. However, to entangle distant Er3+ ions through photonic connections, the emission frequency of individual Er3+ in solid-state matrix must be the same, which is challenging because the emission frequency of Er3+ depends on its local environment. Herein, we propose and experimentally demonstrate the Stark tuning of the emission frequency of a single Er3+ in a Y2SiO5 crystal by employing electrodes interfaced with a silicon photonic crystal cavity. We obtain a Stark shift of 182.9±0.8 MHz, which is approximately 27 times of the optical emission linewidth, demonstrating promising applications in tuning the emission frequency of independent Er3+ into the same spectral channels. Our results provide a useful solution for construction of scalable quantum networks based on single Er3+ and a universal tool for tuning emission of individual rare-earth ions.
We report on the coupling of the emission from a single europium-doped nanocrystal to a fiber-based microcavity under cryogenic conditions. As a first step, we study the properties of nanocrystals that are relevant for cavity experiments and show that embedding them in a dielectric thin film can significantly reduce scattering loss and increase the light–matter coupling strength for dopant ions. The latter is supported by the observation of a fluorescence lifetime reduction, which is explained by an increased local field strength. We then couple an isolated nanocrystal to an optical microcavity, determine its size and ion number, and perform cavity-enhanced spectroscopy by resonantly coupling a cavity mode to a selected transition. We measure the inhomogeneous linewidth of the coherent transition and find a value that agrees with the linewidth in bulk crystals, evidencing a high crystal quality. We detect the fluorescence from an ensemble of few ions in the regime of power broadening and observe an increased fluorescence rate consistent with Purcell enhancement. The results represent an important step towards the efficient readout of single rare earth ions with excellent optical and spin coherence properties, which is promising for applications in quantum communication and distributed quantum computation.