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Quantum Computing, Communication, and Simulation

Efficient collection of zero-phonon line emission from a single silicon T center

Chang-Min Lee, Fariba Islam, Samuel Harper, Mustafa Atabey Buyukkaya, Kartik A. Srinivasan, Daniel B. Higginbottom, Stephanie Simmons, Edo Waks A

Published Mar 13, 2024• 0 citations
Publisher

Abstract

T centers in silicon could serve as efficient quantum memories based on spin-photon interface. But these emitters have long excited state lifetimes and are therefore dim. We demonstrate high-efficiency single photon emission from the zero-phonon line of a single T center using a nanobeam. The tapered nanobeam features coupling efficiency of 71% into a lensed fiber, enabling an order of magnitude improvement in photon count rates as compared to previously reported values. Consequently, we demonstrate single photon emission from the zero-phonon line, representing the coherent emission from the T center. Our result is an important step towards CMOS-integrated spin-photon interfaces.

DOI
10.1117/12.3002748

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quant-pharXiv:2609.32205•Sep 29, 2026
T centers in silicon could serve as efficient quantum memories based on spin-photon interface. But these emitters have long excited state lifetimes and are therefore dim. We demonstrate high-efficiency single photon emission from the zero-phonon line of a single T center using a nanobeam. The tapered nanobeam features coupling efficiency of 71% into a lensed fiber, enabling an order of magnitude improvement in photon count rates as compared to previously reported values. Consequently, we demonstrate single photon emission from the zero-phonon line, representing the coherent emission from the T center. Our result is an important step towards CMOS-integrated spin-photon interfaces.
Color centers in Si could serve as both efficient quantum emitters and quantum memories with long coherence times in an all-silicon platform. Of the various known color centers, the T-center holds particular promise because it possesses a spin ground state that has long coherence times, but this color center exhibits a long excited state lifetime that results in a low-photon emission rate, requiring methods to extract photon emission with high efficiency. We demonstrate high-efficiency single-photon emission from a single T-center using a nanobeam. The nanobeam efficiently radiates light in a mode that is well-matched to a lensed fiber, enabling us to couple over 70% of the photons in the nanobeam directly into a single-mode fiber. This efficiency enables us to directly demonstrate single-photon emission from the zero-phonon line, which represents the coherent emission from the T-center. Our results represent an important step toward silicon-integrated spin–photon interfaces for quantum computing and quantum networks.
Monolithic integration of single-photon sources into silicon photonics offers a compelling solution for realizing scalable quantum telecommunication architectures. Among the candidate silicon color centers, the C-center features a zero-phonon emission in the telecom L-band, corresponding to the spectral window of minimum transmission loss in optical fibers. Despite this advantage, isolating single C-centers has remained an unrealized challenge in solid-state quantum optics. In this work, we report the isolation of a single silicon C-center. We enhance the spontaneous emission rate of the zero-phonon line by coupling the single emitter to a nanophotonic crystal cavity, observing a fivefold reduction in the excited-state lifetime compared to bulk conditions, which corresponds to a Purcell factor lower bound of 33. Second-order autocorrelation measurements confirm single-photon emission from the investigated defect, obtaining an optical purity of g(2)(0)=0.23g^{(2)}(0) = 0.23g(2)(0)=0.23 without background correction. Our results establish a native telecom L-band quantum light source in silicon, laying the foundation for ultra-low-loss and long-distance quantum applications.
Novel T centers in silicon hold great promise for quantum networking applications due to their telecom band optical transitions and the long-lived ground state electronic spins. An open challenge for advancing the T center platform is to enhance its weak and slow zero phonon line (ZPL) emission. In this work, by integrating single T centers with a low-loss, small mode-volume silicon photonic crystal cavity, we demonstrate an enhancement of the fluorescence decay rate by a factor of F = 6.89. Efficient photon extraction enables the system to achieve an average ZPL photon outcoupling rate of 73.3 kHz under saturation, which is about two orders of magnitude larger than the previously reported value. The dynamics of the coupled system is well modeled by solving the Lindblad master equation. These results represent a significant step towards building efficient T center spin-photon interfaces for quantum information processing and networking applications.
Silicon is an attractive host for scalable quantum photonics, but the absence of bright telecom-band emitters with optically addressable spin states has limited its use for spin-photon interfaces. Here we demonstrate the Al1-center, an aluminum--carbon defect in silicon, as a bright waveguide-integrated single-photon emitter with a ground-state spin. Using isotopically purified silicon-on-insulator nanophotonic devices, we isolate individual Al1-centers and observe high-purity single-photon emission with g(2)(0)=0.04g^{(2)}(0)=0.04g(2)(0)=0.04 without background subtraction. Time-resolved photoluminescence spectroscopy reveals a fast excited-state lifetime of 135 ns, nearly an order of magnitude shorter than the benchmark provided by the well-studied T-center. Resonant photoluminescence excitation measurements further resolve the zero-phonon transition and reveal a narrow homogeneous linewidth reaching 47 MHz, threefold narrower than the T-center under comparable temperature. Through magneto-optical spectroscopy, we resolve the spin-dependent transitions of the bound-exciton manifold and achieve spin-selective optical pumping, fulfilling the prerequisite for quantum state initialization and readout. These results establish the Al1-center as a bright telecom-band spin-photon interface in silicon photonics and introduce a promising platform for integrated quantum networks.
Silicon G centers show significant promise as single photon sources in a scalable silicon platform. But these color centers have large nonradiative decay and a low Debye-Waller factor, limiting their usability in quantum applications. In this work, we demonstrate bright Purcell-enhanced emission from a silicon G center by coupling it to a nanophotonic cavity. The nanobeam cavity enhances the spontaneous emission rate of a single G center by a factor of 6, corresponding to a Purcell factor greater than 31 when accounting for decay into the phonon sideband. We obtain a spontaneous emission rate of 0.97 ns, which is the fastest single photon emission rate reported in silicon. With this radiative enhancement, we achieve an order of magnitude improvement in emitter brightness compared to previously reported values. These results pave the way for scalable quantum light sources on a silicon photonic chip.
Telecom-band spin defects in silicon offer a compelling platform for integrated quantum networks by combining scalable silicon photonics with spin-based quantum memories and multiqubit registers. The T center and recently demonstrated Al1 center are particularly promising, but their limited coherent zero-phonon emission requires strong cavity enhancement for efficient spin-photon interfaces. Here, we inverse-design silicon nanobeam cavities for both centers using a unified adjoint-optimization framework targeting Purcell enhancement, resonance alignment, and photon extraction. For each emitter, symmetric cavities maximize Purcell enhancement, while asymmetric cavities provide directional coupling to an integrated waveguide. Three-dimensional finite-difference time-domain simulations yield loaded quality factors up to 3.25 x 10^6, Purcell factors up to 1.43 x 10^5, and cooperativities of approximately 280-5000, corresponding to cavity-coupled emission fractions exceeding 99.6%. The asymmetric cavities direct approximately 90% of emitted power into a single on-chip waveguide while maintaining cooperativity above 280. Under nanometer-scale fabrication perturbations, all four designs remain within the high-cooperativity regime, and high cooperativity persists when the cavity quality factor is constrained to a realistic absorption-limited value of 10^5. This unified, fabrication-compatible framework establishes a scalable cavity-design route for silicon telecom spin-photon interfaces and, to our knowledge, the first cavity designs for the Al1 center.