Implementation of large-scale quantum networks have the potential to augment the capabilities of existing quantum information technologies. By linking quantum processors over photonic channels, future quantum networks could enable applications such as remote quantum sensing, distributed quantum computing, and secure quantum communication. Atomic defects in solids are readily integrated with photonic structures, making them promising candidates for use in quantum networking devices. In particular, the silicon material platform holds great promise due to the technologically mature silicon electronic and photonic industries. The T center defects in silicon possess telecom O-band optical transitions, as well as long-lived electronic and nuclear spins, making it the focus of particular interest. These spin and optical properties of single T centers, together with their accessibility to the existing integrated electronic and photonic technologies, opening the door to modular long-distance quantum networking technologies built on the T center platform. This work outlines the integration of single T centers with a silicon photonic crystal cavity; we observe cavity-enhanced fluorescence emission, resulting in a decay rate enhancement factor of F = 6.89 compared to the bulk emission rate. Through the use of silicon photonic circuits and an angle-polished fiber for light coupling, we achieve a maximum zero phonon line photon outcoupling rate of 73.3 kHz. The design and fabrication of the nanophotonic cavity used in experiment is detailed. This work represents a major step towards use of the silicon T center as a telecom spin-photon interface in future quantum networking applications.
Implementation of large-scale quantum networks have the potential to augment the capabilities of existing quantum information technologies. By linking quantum processors over photonic channels, future quantum networks could enable applications such as remote quantum sensing, distributed quantum computing, and secure quantum communication. Atomic defects in solids are readily integrated with photonic structures, making them promising candidates for use in quantum networking devices. In particular, the silicon material platform holds great promise due to the technologically mature silicon electronic and photonic industries. The T center defects in silicon possess telecom O-band optical transitions, as well as long-lived electronic and nuclear spins, making it the focus of particular interest. These spin and optical properties of single T centers, together with their accessibility to the existing integrated electronic and photonic technologies, opening the door to modular long-distance quantum networking technologies built on the T center platform. This work outlines the integration of single T centers with a silicon photonic crystal cavity; we observe cavity-enhanced fluorescence emission, resulting in a decay rate enhancement factor of F = 6.89 compared to the bulk emission rate. Through the use of silicon photonic circuits and an angle-polished fiber for light coupling, we achieve a maximum zero phonon line photon outcoupling rate of 73.3 kHz. The design and fabrication of the nanophotonic cavity used in experiment is detailed. This work represents a major step towards use of the silicon T center as a telecom spin-photon interface in future quantum networking applications.
Quantum networks represent one of the most promising technologies for the future development of quantum information science (QIS), with broad applications that range from secure communication and distributed quantum computing to enhanced sensing. Solid-state platforms are ideal candidates for the implementation of such quantum networks, since they offer easy accessibility to device integration and spin-photon interfaces capable of processing and storing qubits, as well as connecting remote network nodes by sending photons through optical fibers. In this thesis, we focus on single T centers, which are a novel type of color centers in silicon. This quantum defect stands out as a promising candidate for quantum networking applications due to its telecom optical transition, superior spin performance, and its compatibility with the technologically mature silicon platform. Here, we present our initial studies on single T centers, including the design and fabrication of nanophotonic devices in a silicon-on-insulator (SOI) sample with integrated T centers, and the cavity-enhanced fluorescence emission of single T centers, which have achieved the highest Purcell factor (Pt = 43) to date. Moreover, our experimental and numerical results allow us to determine a lower bound to the T center quantum efficiency of η = 23.4%, which is a key optical parameter for T centers that is largely overlooked in the community. Additionally, we present preliminary bulk spectroscopy work on ensemble T centers. The same setup will be exploited towards the exploration of novel quantum defects in silicon, including the boron-carbon (B-C) complex defect and the Ti+ defect, which are expected to have similar or better optical properties than the T center.
Quantum networking is a crucial technology towards constructing large-scale distributed quantum systems. The structure of photonic link and distributed network nodes allows high-speed and high-fidelity interconnect, enabling various applications such as distributed quantum computing and sensing, as well as secure quantum communications. Optically interfaced solid-sate spins are promising candidates for building a quantum network due to their active spin-photon interfaces, compatibility, and scalability for device integration. Especially for defect spins in silicon, the platform benefits from mature silicon photonic industry, and can access to the integration techniques developed over the past decades. T center in silicon particularly holds great expectations because of the telecom-O band optical interface, ground state doublet spin manifold, and long-lived nuclear spin coherence. Their telecom spin-photon interface provides a direct link between stationary quantum memory and flying qubits that are compatible with the existing telecommunication fiber network infrastructure. This work focuses on investigating cavity quantum electrodynamics (cQED) for cavity-coupled single T centers, its applications in quantum optical control of T center optical properties, and in realizing single-shot spin state readout. The cavity enhanced light-matter interaction mitigates the caveats of T center, such as long radiative lifetime, low Debye-Waller factor, and lack of polarization selection rule for the optical transitions. In this work, by integrating single T centers with a low-loss, small mode volume silicon photonic cavity, we have achieved the Purcell enhancement for boosting the T center fluorescence rate with a factor of 6.89. We build up the theoretical framework based on the Jaynes-Cummings model and Lindblad master equation to explain experimental observations and reveal cQED parameters. The further study on the electronic spin state readout is carried out as the fast, high-fidelity single-shot readout is critical for quantum information processing. Two methods are proposed based on realistic cQED parameters: resonant fluorescence readout in the low-cooperativity regime and spin-dependent cavity-reflection readout for intermediate- and high-cooperativity regimes. Both approaches demonstrate feasibility of high-fidelity (F > 0.95) readout, particularly the reflection readout allows F > 0.99 within a short readout time of 50 μs. This work demonstrates a promising telecom spin-photon interface with high-fidelity readout based on cavity-coupled single T centers in silicon, which are promising candidates for building future large-scale 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)=0.23 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.
Solid-state quantum light sources offer a scalable pathway for interfacing stationary spin qubits with flying photonic qubits, forming the backbone of future quantum networks. Telecom-band spin-photonic qubits, operating in the 1260-1675 nm wavelength range, are particularly well-suited for long-distance quantum communication due to minimal loss in standard optical fibers. Achieving scalability, however, hinges on fulfilling several stringent criteria: coherent spin-state control, deterministic and indistinguishable single-photon emission, and integration with nanophotonic structures that enhance radiative properties, such as lifetime, coherence, and photon indistinguishability. This study explores the state-of-the-art spin-photonic qubits across solid-state platforms, including diamond color centers, silicon carbide defect centers, quantum dots, and two-dimensional materials. Special attention is given to silicon-based emitters, particularly G, T, C- and Ci-centers, which promise monolithic integration with complementary metal-oxide-semiconductor (CMOS) technology and telecom-band operation. We classify these systems based on spin-photon interface availability, CMOS process compatibility, and emitter scalability. We also discuss recent advances in cavity quantum electrodynamics (cQED), including Purcell enhancement and quality factor engineering in integrated photonic (circuits) environments. The work highlights emerging demonstrations of quantum networking over metropolitan scales and outlines the trajectory toward chip-scale quantum photonic integrated circuits (QPICs). It combines deterministic emitter creation, coherent spin manipulation, and quantum information processing. These developments pave the way for global quantum networks, enabling secure communication, distributed quantum computing, and quantum-enhanced sensing.
Artificial atoms in solids are leading candidates for quantum networks, scalable quantum computing, and sensing, as they combine long-lived spins with mobile photonic qubits. Recently, silicon has emerged as a promising host material where artificial atoms with long spin coherence times and emission into the telecommunications band can be controllably fabricated. This field leverages the maturity of silicon photonics to embed artificial atoms into the world's most advanced microelectronics and photonics platform. However, a current bottleneck is the naturally weak emission rate of these atoms, which can be addressed by coupling to an optical cavity. Here, we demonstrate cavity-enhanced single artificial atoms in silicon (G-centers) at telecommunication wavelengths. Our results show enhancement of their zero phonon line intensities along with highly pure single-photon emission, while their lifetime remains statistically unchanged. We suggest the possibility of two different existing types of G-centers, shedding new light on the properties of silicon emitters.