Erbium-doped single crystal diamond materials for enabling narrow-linewidth quantum communication in the telecom band

Background

Quantum communication is an emerging field that leverages the principles of quantum mechanics to enable ultra-secure data transmission and advanced information processing. A critical requirement for practical quantum networks is the ability to generate and manipulate quantum states of light at wavelengths compatible with existing telecommunications infrastructure, particularly in the telecom C-band (1530–1565 nm), where optical fibers exhibit minimal loss. Rare earth ions, especially erbium (Er3+), are uniquely suited for this purpose due to their emission in the C-band, making them highly attractive for quantum repeaters and memory devices. Diamond, as a host material, offers exceptional properties such as a wide bandgap, high chemical stability, and low intrinsic magnetic noise, which are advantageous for preserving quantum coherence and enabling robust device operation.

Despite these advantages, current approaches to integrating rare earth ions like erbium into diamond or other host crystals face significant challenges. Ion implantation, the standard method for introducing rare earth elements, often causes substantial lattice damage in the crystal, leading to degraded optical and spin properties of the resulting defects. Furthermore, most host crystals suffer from high levels of magnetic noise due to impurities such as nitrogen, which severely limits the spin coherence times essential for quantum information applications. Achieving the necessary combination of high optical quality, precise dopant placement, low impurity content, and minimal strain has proven difficult with conventional fabrication techniques. As a result, the performance and scalability of quantum devices based on these materials remain constrained, impeding progress toward practical quantum communication networks.

Technology

The described technology is an advanced erbium-doped single crystal diamond engineered for quantum communication applications, particularly those operating in the telecom C-band (1530–1565 nm). This material is characterized by its ability to emit photoluminescence at 1508 nm with an exceptionally narrow spectral linewidth (less than 1.0 nm) and a short decay lifetime (under 4 microseconds), making it ideal for high-fidelity optical signaling. The erbium concentration is precisely controlled between 20 and 80 ppm and is localized within a thin surface layer of 500 nm or less, while the diamond’s single substitutional nitrogen content is kept below 10 ppb to minimize magnetic noise. The fabrication process involves pre-etching the diamond with inductively coupled plasma to reduce surface strain, followed by ion implantation of erbium at energies between 10 and 350 keV, and a high-pressure, high-temperature annealing step (at least 5 GPa and 1600°C) to repair lattice damage and stabilize the optically active defects. The resulting diamond exhibits low surface roughness (≤10 nm) and minimal optical birefringence, ensuring high optical quality and device reliability.

This technology is differentiated by its unique combination of material purity, precise dopant control, and advanced processing techniques that collectively address longstanding challenges in quantum device fabrication. Unlike previous attempts to integrate rare earth ions into diamond—which often resulted in degraded optical properties due to lattice damage and magnetic noise—this solution leverages a carefully optimized sequence of surface preparation, ion implantation, and HPHT annealing to produce stable, optically addressable erbium centers with narrow emission lines and minimal background interference. The ultra-low nitrogen content and controlled erbium distribution significantly enhance spin coherence times and optical performance, making the material exceptionally well-suited for quantum communication devices that require operation in the telecom C-band. Furthermore, the scalable and reproducible fabrication method enables integration into practical quantum networks, positioning this solution as a critical enabler for next-generation secure communication technologies.

Benefits

• Enables narrow-linewidth photoluminescence at 1508 nm within the telecom C-band, ideal for low-loss quantum communication over optical fibers.
• Provides short photoluminescence lifetime (<4 microseconds), supporting fast optical addressing and quantum operations.
• Maintains extremely low magnetic noise through ultra-pure diamond (<10 ppb nitrogen), enhancing spin coherence and quantum performance.
• Confines erbium dopants to a thin, well-controlled surface layer (≤500 nm), enabling precise defect engineering and device integration.
• Utilizes a fabrication process (ICP etching, ion implantation, HPHT annealing) that repairs lattice damage and stabilizes optically active erbium centers.
• Achieves low surface roughness and minimal optical birefringence, reducing strain and improving optical quality and uniformity.
• Results in stable, optically addressable erbium defects suitable for scalable quantum communication devices and systems.

Applications

• Quantum communication repeaters
• Telecom C-band quantum memories
• Single-photon sources for fiber networks
• Quantum key distribution devices

Additional info

This erbium-doped single crystal diamond exhibits photoluminescence at 1508 nm with a spectral linewidth under 1.0 nm and decay lifetime below 4 microseconds. It maintains 20–80 ppm rare earth concentration within a 500 nm surface layer and nitrogen levels below 10 ppb. Produced through ICP etching, ion implantation, and HPHT annealing at 5 GPa and 1600°C, this low-birefringence material is engineered for high-performance quantum communication devices.