Spin-photon Qubits Operating at 1260-1675nm Enable Scalable Quantum Networks with Solid-State Integration

The development of scalable quantum networks demands efficient connections between stationary quantum bits (qubits) and flying photonic qubits, and researchers are actively pursuing solid-state light sources to achieve this crucial interface.

Md Sakibul Islam, Kuldeep Singh, Yunhe Zhao, Nitesh Singh, and Wayesh Qarony, all from the University of Central Florida, investigate the most promising solid-state platforms for creating these spin-photon qubits, focusing on materials like diamond, silicon carbide, and innovative silicon-based emitters. Their work addresses the critical requirements for scalability, precise control of qubit states, reliable single-photon emission, and seamless integration with nanophotonic structures, and classifies these systems based on compatibility with existing technology and potential for large-scale production. By exploring advances in cavity electrodynamics and demonstrating networking over metropolitan distances, this research highlights a clear trajectory towards compact, chip-scale photonic integrated circuits that will underpin future global quantum networks, enabling secure communication, distributed computing, and advanced sensing capabilities. Silicon Defects for Quantum Light Sources Scientists are investigating defects and impurities within silicon as potential building blocks for future quantum technologies, specifically for creating reliable sources of single photons and developing quantum memories. These components are essential for advancements in quantum communication and computation, offering the potential for secure data transmission and powerful new computing paradigms. Research focuses on harnessing the unique optical properties of these defects to control and manipulate quantum information. Several types of defects are under scrutiny, each with distinct characteristics. Carbon-related defects, such as interstitial carbon and carbon vacancies, are being explored for their ability to emit light. Erbium, a rare-earth element incorporated into silicon, is a strong candidate for both quantum memories and single-photon sources, particularly because its emission wavelength aligns with the standard telecom band used in fiber optic communication. Enhancing Erbium’s performance involves combining it with oxygen and integrating it with nanophotonic structures to improve light interaction. Key concepts driving this research include Purcell enhancement, which uses nanophotonic structures to confine light and increase emission rates, and achieving telecom-band emission, crucial for compatibility with existing fiber optic networks. Maintaining long coherence times, a measure of how long quantum information can be stored, is also paramount for effective quantum memories. Researchers employ techniques like molecular beam epitaxy to precisely control defect concentrations and silicon-on-insulator technology to create nanophotonic devices. Current efforts involve using high-purity, isotopically enriched silicon to minimize spectral broadening and improve defect performance. Scientists are also focused on precisely controlling the type and concentration of defects within silicon and integrating them with nanophotonic structures to create efficient single-photon sources and quantum memories.

This research aims to leverage the existing infrastructure of silicon manufacturing to create scalable quantum devices, paving the way for practical quantum technologies. Silicon Telecom-Band Qubit Development and Control Scientists are developing solid-state light sources to connect stationary and flying quantum bits, forming the foundation for future quantum networks. Their work centers on telecom-band spin-photonic qubits, operating within a specific wavelength range that minimizes signal loss during long-distance communication. Achieving scalability requires precise control of spin states, deterministic emission of single photons, and integration with nanophotonic structures to optimize radiative properties like lifetime and coherence. Researchers are concentrating on specific defects in silicon, including G, T, C-, and Ci-centers, due to their potential for integration with complementary metal-oxide-semiconductor (CMOS) technology and operation within the telecom band. These systems are classified based on their ability to interface with photons, compatibility with CMOS processing, and potential for mass production.

The team is also exploring advanced cavity electrodynamics, including Purcell enhancement and quality factor engineering within integrated photonic circuits, to improve light-matter interactions. Experiments demonstrate networking over metropolitan distances and pave the way for chip-scale photonic integrated circuits. Scientists utilize annealing processes, crucially incorporating hydrogen co-doping, to create high densities of Ci-centers. Implanting carbon isotopes into silicon-on-insulator wafers and annealing at high temperatures yields Ci-centers emitting at a specific wavelength while suppressing unwanted defects. They employ femtosecond lasers to precisely activate and deactivate Ci-centers, enabling deterministic placement of single emitters directly within prefabricated photonic circuits. The Ci-center exhibits a narrow emission line within the telecom band and displays exceptionally narrow linewidths, limited only by the resolution of measurement instruments. Time-resolved measurements reveal fast radiative lifetimes, enabling highly indistinguishable photon emission, particularly when using isotopically enriched silicon. The Ci-center possesses a paramagnetic ground state and two optically addressable charge states, making it a promising candidate for a spin-photon qubit.

Scientists have isolated single Ci-centers with controlled positioning, achieving high yields and producing clean single-photon emission, enabling precise defect placement crucial for building complex quantum circuits. Telecom-Band Spin Qubits in Silicon Solid-state light sources are crucial for building scalable quantum networks, interfacing stationary spin qubits with flying photonic qubits. Researchers have focused on telecom-band spin-photonic qubits, operating within a specific wavelength range to minimize signal loss in standard optical fibers. This work comprehensively examines solid-state qubit platforms, classifying them by spin-photon interface availability, compatibility with standard manufacturing processes, and potential for scaling up production. The study highlights silicon-based emitters, specifically G, T, C- and Ci-centers, as promising candidates for integration with complementary metal-oxide-semiconductor (CMOS) technology. Experiments demonstrate that initializing a spin into a coherent superposition of states using microwave or radio frequency pulses, followed by optical excitation, results in photon emission carrying information about the spin qubit. Verification of spin-photon entanglement relies on joint measurements of both spin and photonic properties, with high-visibility correlations confirming entanglement and enabling quantum protocols like entanglement swapping and quantum teleportation. These protocols have been successfully demonstrated over kilometer-scale fiber links using nitrogen-vacancy (NV) centers in diamond, across metropolitan distances with silicon-vacancy (SiV) centers in integrated nanophotonics, and in free-space and fiber networks with III-V quantum dots. Researchers achieved demonstrations of networking over metropolitan scales and are progressing towards chip-scale photonic integrated circuits. The study evaluated five principal material systems, diamond, III-V quantum dots, silicon carbide, two-dimensional materials, and silicon, based on emission wavelength, zero-phonon line (ZPL) fraction, spin coherence times, optical lifetimes, and photon statistics. Diamond defect centers, particularly nitrogen-vacancy (NV) and silicon-vacancy (SiV) centers, have proven foundational, enabling key milestones in quantum information science. Experiments with SiV centers demonstrate efficient coupling between long-lived spin qubits and photonic flying qubits, enhancing entanglement distribution for scalable quantum networks.

Silicon Defects Advance Quantum Technologies Solid-state quantum emitters have experienced significant advances, offering multiple pathways towards scalable quantum technologies. Researchers have demonstrated essential quantum functionalities, long spin coherence, high-purity single-photon emission, and integration with nanophotonic structures, across diverse platforms including diamond color centers, quantum dots, silicon carbide defects, and two-dimensional materials. These systems have facilitated landmark demonstrations in quantum communication, sensing, and computation, though each platform presents trade-offs between emission wavelength, scalability, and fabrication complexity. Silicon defect centers and dopants now represent a particularly promising area of development. Their intrinsic telecom-band optical transitions ensure compatibility with existing fiber infrastructure, while silicon’s established CMOS processing benefits from decades of industrial maturity. Recent achievements include coherent spin control of single G centers, multi-qubit spin registers in T centers, narrow linewidth emission from Ci centers, and optically detected magnetic resonance in C centers, demonstrating the rich quantum functionalities achievable within silicon. Integration with silicon photonics further enables low-loss routing, enhanced cavity properties. 👉 More information 🗞 Spin-photon Qubits for Scalable Quantum Network 🧠 ArXiv: https://arxiv.org/abs/2512.06285 Tags: