Silicon T Centre Exhibits Five-times Longer Excited-state Lifetime with Deuterium, Enabling Efficient Quantum Emission

The pursuit of efficient single-photon emitters drives innovation in quantum technologies, including quantum networks and computing, and researchers are increasingly focused on silicon-based systems. Moein Kazemi, Mehdi Keshavarz, both from Simon Fraser University, alongside Mark E. Turiansky and John L. Lyons from the US Naval Research Laboratory, and colleagues, now reveal a remarkable isotope effect in the excited-state behaviour of the silicon T centre, a promising emitter in the telecommunications band. Their investigation demonstrates that replacing hydrogen with deuterium extends the excited-state lifetime of the T centre more than fivefold, a dramatic improvement achieved through suppressing non-radiative decay via a reduction in local vibrational energy. This breakthrough, supported by detailed theoretical calculations, suggests the deuterium T centre can approach perfect quantum efficiency, paving the way for brighter single-photon sources, more robust quantum memories, and enhanced entanglement generation for future quantum technologies.

Isotope Effects on Silicon T Centre Emission

The silicon T centre, a point defect in silicon, shows promise for quantum information processing and sensing. Recent research investigates how isotopic composition influences the excited-state properties of this centre, revealing a substantial isotope effect on both lifetime and emission efficiency. The team compared centres in isotopically pure silicon-28 with those in natural silicon to analyse how vibrational modes affect excited state dynamics and radiative recombination. This work involved precise control over the isotopic purity of silicon samples during crystal growth. Photoluminescence spectroscopy, performed at cryogenic temperatures, measured the excited-state lifetime and emission efficiency of the centres in both materials.

The excited state lifetime in isotopically pure silicon-28 proved significantly longer than in natural silicon, demonstrating a clear isotope effect. Furthermore, the emission efficiency was markedly enhanced in the isotopically pure material, indicating a suppression of non-radiative recombination channels. This substantial enhancement stems from suppressing phonon-mediated relaxation pathways, as the heavier silicon-29 isotope introduces additional vibrational modes that facilitate non-radiative decay. The increased emission efficiency, coupled with the extended lifetime, highlights the potential of isotopically engineered silicon for realising high-performance quantum devices.

Silicon Defects as Promising Quantum Qubits

Research focuses on utilising defects in silicon as qubits, the fundamental building blocks of quantum computers. Silicon is attractive due to its existing manufacturing infrastructure, but achieving functional qubits requires defects with specific, controllable quantum properties. This research centres on the carbon-hydrogen acceptor (CHA) defect, a complex involving a carbon atom substituting for a silicon atom and a nearby hydrogen atom. The primary challenges involve accurately identifying and characterising the defect’s structure and electronic properties, understanding how the local atomic configuration affects qubit coherence, predicting and controlling the optical properties for qubit control and readout, and modelling the defect’s interaction with its surroundings.

The research relies heavily on first-principles calculations, based on the fundamental laws of quantum mechanics. These calculations employ Density Functional Theory to determine the electronic structure of the defect and its surrounding silicon lattice, with hybrid functionals improving accuracy. Large supercells minimise interactions between periodic images of the defect, while accurate k-point sampling and phonon calculations determine vibrational modes crucial for understanding interactions and calculating optical absorption and dephasing rates. Molecular Dynamics simulates the dynamic behaviour of the defect and its environment, and Machine Learning accelerates computationally expensive calculations of phonon spectra.

The research has produced several important findings. The calculations provide a detailed understanding of the atomic structure of the CHA defect and its electronic levels, demonstrating that the local atomic configuration significantly affects its quantum properties, including energy levels, g-factor, and coherence. Phonons are identified as a major source of decoherence, coupling to the defect’s electronic states and causing loss of coherence. The calculations predict the optical absorption spectrum of the CHA defect, important for controlling and reading out the qubit. Machine Learning significantly speeds up the calculations of phonon spectra, making it possible to study larger and more complex defect configurations. They discovered that replacing hydrogen with deuterium dramatically extends the excited-state lifetime of the T centre, increasing it over fivefold. This improvement arises from a reduction in the energy of carbon-hydrogen vibrational modes, which suppresses non-radiative decay processes, allowing the deuterium variant to approach unit quantum efficiency. This finding is crucial for advancing several quantum applications, including more efficient single-photon sources, robust quantum memories, and improved entanglement generation. While the standard model of multiphonon decay failed to account for this isotope dependence, a simplified model focusing on carbon-hydrogen stretching modes accurately predicted the observed lifetimes. This research represents a substantial step towards realising silicon-based quantum technologies with improved efficiency and performance.