Silicon T Center Achieves Long-Distance Quantum Communication with Enhanced Fidelity

The pursuit of stable and efficient quantum networks hinges on identifying and harnessing systems that can both transmit and store quantum information, and researchers are increasingly focused on spin-interface (SPI) platforms to achieve this goal. Nicholas Brunelle, Joshua Kanaganayagam, and Mehdi Keshavarz, all from Simon Fraser University, alongside colleagues including Chloe Clear and Oney Soykal, investigate the silicon T centre, a promising SPI with unique properties for building such networks. This research determines the precise hyperfine coupling within the T centre, revealing crucial details about how its internal quantum bits interact, and introduces innovative methods to shield the T centre’s memory qubit from disruptive environmental noise during operation. By addressing a key challenge in maintaining qubit stability, this work represents a significant step towards realising practical, long-distance quantum communication using silicon-based technology.

Silicon Color Centers as Promising Qubits

Research into silicon-based quantum technologies focuses on utilizing color centers, such as the ‘T center’ and Group-IV centers in both diamond and silicon, as potential qubits, the fundamental building blocks of quantum computers. Silicon offers a strong advantage for scalable quantum technologies because its compatibility with existing semiconductor manufacturing processes allows for potentially cost-effective and large-scale production. A major challenge in this field is decoherence, the loss of quantum information, caused by interactions with the surrounding environment. Researchers are exploring techniques like isotopic purification and dynamic decoupling to minimize these interactions and extend qubit coherence times. Furthermore, scientists are investigating architectures for distributed quantum computing, connecting multiple silicon-based qubit modules to enhance scalability and exploring hybrid approaches that combine silicon color centers with other qubit technologies. These efforts aim to create cell-based architectures, consisting of interconnected groups of qubits, to build more powerful and complex quantum systems.

T Centre Hyperfine Coupling via ODMR Spectroscopy

Scientists meticulously characterized the T center, a point defect in silicon with potential for quantum networking, by precisely determining its hydrogen hyperfine coupling tensor. They employed optically-detected magnetic resonance (ODMR) to resolve the ground state level structure of the T center, enabling detailed analysis beyond the limits of conventional optical resolution. The experimental setup involved exciting an ensemble of T centers with a near-infrared laser and detecting the resulting light with a sensitive detector. Radio frequency and tunable magnetic fields were applied to manipulate and probe the T center’s spin states. Researchers utilized an isotopically purified silicon crystal with a high carbon concentration, maintained at extremely low temperatures, to minimize environmental noise. ODMR spectra revealed a unique grouping of energy levels, differing significantly from simple hyperfine coupling, allowing the team to extract the hydrogen hyperfine tensor, a crucial parameter for understanding and controlling the T center’s spin properties.

Silicon T Centres Exhibit Narrow Linewidths

Scientists have achieved a significant breakthrough in developing robust quantum networks by characterizing the hydrogen hyperfine coupling within silicon T centers, a promising platform for spin-photon interfaces. Measurements reveal that the T center possesses remarkably narrow homogeneous linewidths, as narrow as 0.69MHz, making it ideal for integration into silicon photonic nanostructures like waveguides and cavities. Long spin coherence times, exceeding 2 milliseconds for the electron spin and 1 second for the nuclear spin, further enhance its potential for quantum information processing. Through detailed analysis, scientists unambiguously determined the hyperfine coupling tensor, a crucial parameter for understanding and controlling the interaction between the electron and nuclear spins. They modeled the impact of magnetic fields on memory qubit decoherence during optical excitation, identifying operational conditions that preserve the nuclear spin qubit state during remote entanglement attempts. These findings demonstrate the potential for building scalable quantum networks utilizing the T center’s inherent spin register, where the electron and nuclear spins can be assigned communication and memory roles respectively.

Silicon T Centre Decoherence Suppression Demonstrated

This work presents precise measurements of the silicon T center’s ground-state structure and, for the first time, determines the anisotropic hyperfine coupling between its bound electron and hydrogen nucleus. Researchers also identified a dephasing protection manifold, demonstrating the possibility of selecting external magnetic fields that eliminate optically-induced nuclear spin decoherence. The demonstrated ability to suppress decoherence is particularly significant, as it enables high-fidelity entanglement between cavity-coupled T centers within silicon photonic circuits and across fibre networks, supporting the development of networked quantum computing and secure quantum communication technologies. Researchers acknowledge that further research is needed to fully explore the potential of these T centers, particularly in extending these findings to the carbon nuclei and implementing more sophisticated quantum logic.