Eliminating cryogenic operating requirements while preserving microsecond-scale quantum coherence and enabling CMOS scalability remains a central challenge for telecom quantum technologies. Addressing this, we introduce a CMOS-compatible quantum system comprising single-erbium-(Er)-ion qudits (five-level systems) operating across the visible and telecom C-band. Through innovative nanofabrication, we achieve self-aligned ion placement, enabling spatial isolation of single-Er ions and suppressing dephasing. We realize individually addressable single-Er-devices with record-long optical coherence times in the telecom C-band exceeding 500 μs at ambient conditions, a performance previously limited to vacuum conditions at temperatures over 900 times lower. Furthermore, we present the first demonstration of background-free, upconversion-enabled single-photon Er-emissions providing coherent, high-contrast optical readouts. This work showcases the first room-temperature single-Er-qudit system with unprecedented properties enabling next-generation cryogen-free telecom quantum technologies.
Eliminating cryogenic operating requirements while preserving microsecond-scale quantum coherence and enabling CMOS scalability remains a central challenge for telecom quantum technologies. Addressing this, we introduce a CMOS-compatible quantum system comprising single-erbium-(Er)-ion qudits (five-level systems) operating across the visible and telecom C-band. Through innovative nanofabrication, we achieve self-aligned ion placement, enabling spatial isolation of single-Er ions and suppressing dephasing. We realize individually addressable single-Er-devices with record-long optical coherence times in the telecom C-band exceeding 500 μs at ambient conditions, a performance previously limited to vacuum conditions at temperatures over 900 times lower. Furthermore, we present the first demonstration of background-free, upconversion-enabled single-photon Er-emissions providing coherent, high-contrast optical readouts. This work showcases the first room-temperature single-Er-qudit system with unprecedented properties enabling next-generation cryogen-free telecom quantum technologies.
Advancing quantum information science demands solid-state quantum systems that maintain long quantum coherence at elevated temperatures while supporting scalable, CMOS-compatible fabrication and telecom C-band operation. No existing platform has simultaneously achieved these requirements, as state-of-the-art demonstrations of coherent control of erbium ions, with an intrinsic telecom-band optical transition, have been confined to cryogenic temperatures below < 10 K under controlled vacuum conditions. This thesis introduces a new paradigm in which materials science and engineering provides the enabling pathway to quantum coherence. A foundry-compatible nanofabrication approach, paired with targeted materials engineering, is developed to realize a new class of CMOS-scalable quantum system: arrays of spatially isolated single-erbium-ion qudits (five-level systems) embedded in silicon-based (e.g., silicon carbide (SiC) and SiCxOy) hollow nanopillars (HNPs). Non-lithographically defined nanostructure geometries with ≤ 5 nm critical dimensions, achieved through conformal chemical vapor deposition (CVD) with growth rates of ~0.3 Å/s, impose a geometric confinement that self-aligns and spatially isolates individual Er3+ ions with nanometer-scale placement accuracy. Oxygen co-doping during growth introduces Si–C–O defect centers that mediate efficient energy transfer to Er3+ ions, yielding an effective excitation cross section of ~2 × 10−17 cm2, two to three orders of magnitude larger than in bulk crystalline hosts, enabling room-temperature single-ion optical detection without the use of nanophotonic cavities. Within these devices, record-long room-temperature optical quantum coherence in the telecom C-band is demonstrated: T2 = 568 µs via photon echo and T2* = 32 µs via Ramsey interferometry, a performance previously limited to vacuum conditions at temperatures over 900 times lower. Coherent Rabi oscillations are observed with >96% contrast, and pulsed photon-correlation measurements confirm single-photon emission (g2(0) = 0.25) from spatially isolated Er3+ ions at ambient conditions. Furthermore, an upconversion-mediated readout protocol accesses the multi-level qudit structure, producing background-free single-photon emission at 518 nm (g2(0) = 0.06) and 980 nm (g2(0) = 0.18) without the use of an optical cavity, the first such demonstration for erbium. Together, these results establish a materials-driven engineering approach that integrates scalable thin-film growth, nanostructure design, implantation optimization, and quantum-optical characterization, overcoming the fundamental requirement for cryogenic operation in telecom quantum systems. Thus, it establishes a pathway toward revolutionary breakthroughs in cryogenic-free quantum photonic integrated devices for practical, deployable quantum sensing, communication, and networking application
Advancing quantum sensing and photonics requires quantum devices that are compatible with existing wafer-scale processing, enabling scalable integration into photonic integrated circuits (PICs) and operation at higher temperatures (≥77 K). In this context, telecom single-photon emitters and qubits based on single ions/defects in solid-state materials are vital for the development of quantum PICs. However, scaling these materials beyond the lab remains practically elusive due to materials’ constraints and stringent operating conditions, rendering them unsuitable for real-world implementation at the telecom C-band. Our approach utilizes a novel, scalable nanofabrication scheme to address these challenges, enabling the creation of spatially isolated and individually addressable single erbium ion qubits in silicon-based nanopillars, thereby paving the way for significant breakthroughs. Our quantum devices exhibit room-temperature operation and unparalleled characteristics, paving the way for quantum advantage by building a foundry-fabricated quantum sensor platform that is practical for widespread deployment in aerospace applications.
Solid-state spin-based quantum systems have emerged as popular platforms for quantum networking applications due to their optical interfaces, their long-lived quantum memories, and their natural compatibility with semiconductor manufacturing. Photonic crystal cavities are often used to enhance radiative emission; however, fabrication of the necessary subwavelength cavities is typically limited to small batch electron beam lithography. In this work, we demonstrate high quality factor, small mode volume nanobeam cavities fabricated on a scalable silicon photonic foundry platform. The foundry fabricated cavities are then interfaced with single erbium ions through backend deposition of TiO 2 thin films lightly doped with erbium. Single ion lifetime measurements indicate Purcell enhancement up to about 500, thereby demonstrating a route toward manufacturable deterministic single photon sources in the telecom C-band.
Single atoms and atomlike defects in solids are ideal quantum light sources and memories for quantum networks. However, most atomic transitions are in the ultraviolet-visible portion of the electromagnetic spectrum, where propagation losses in optical fibers are prohibitively large. Here, we observe for the first time the emission of single photons from a single Er^{3+} ion in a solid-state host, whose optical transition at 1.5 μm is in the telecom band, allowing for low-loss propagation in optical fiber. This is enabled by integrating Er^{3+} ions with silicon nanophotonic structures, which results in an enhancement of the photon emission rate by a factor of more than 650. Dozens of distinct ions can be addressed in a single device, and the splitting of the lines in a magnetic field confirms that the optical transitions are coupled to the electronic spin of the Er^{3+} ions. These results are a significant step towards long-distance quantum networks and deterministic quantum logic for photons based on a scalable silicon nanophotonics architecture.
Single quantum emitters embedded in solid-state hosts are an ideal platform for realizing quantum information processors and quantum network nodes. Among the currently investigated candidates, Er^{3+} ions are particularly appealing due to their 1.5 μm optical transition in the telecom band as well as their long spin coherence times. However, the long lifetimes of the excited state-generally in excess of 1 ms-along with the inhomogeneous broadening of the optical transition result in significant challenges. Photon emission rates are prohibitively small, and different emitters generally create photons with distinct spectra, thereby preventing multiphoton interference-a requirement for building large-scale, multinode quantum networks. Here we solve this challenge by demonstrating for the first time linear Stark tuning of the emission frequency of a single Er^{3+} ion. Our ions are embedded in a lithium niobate crystal and couple evanescently to a silicon nanophotonic crystal cavity that provides a strong increase of the measured decay rate. By applying an electric field along the crystal c axis, we achieve a Stark tuning greater than the ion's linewidth without changing the single-photon emission statistics of the ion. These results are a key step towards rare earth ion-based quantum networks.
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.