Key Discovery

A recent study has demonstrated that replacing common hydrogen (protium) with a heavier isotope, deuterium, within silicon's T-center defect significantly enhances its ability to produce single photons. This adjustment could have substantial implications for quantum computing and secure communication networks, potentially enabling silicon to power future quantum internet infrastructure.

Understanding the T Center

The T center is a specific defect in a silicon crystal lattice, comprising two carbon atoms and one hydrogen atom. When energized, this defect can emit a single photon, which is crucial for quantum technologies. It is particularly valuable because it emits light in the telecommunications O-band, making it compatible with existing fiber-optic internet cables.

Previously, T centers sometimes lost energy through nonradiative decay – dissipating energy as vibration – instead of emitting light. Scientists did not fully understand why this occurred or how to prevent it.

Isotope Effect and Methodology

Researchers investigated the role of hydrogen isotopes, specifically using deuterium due to its heavier mass, which alters atomic vibrations within the crystal.

The study utilized exceptionally pure silicon crystals, originally developed for the Avogadro project. T centers were created by irradiating the silicon with high-energy particles, followed by specific heating and cooling processes. Three types of samples were prepared: one with natural hydrogen, one infused with deuterium, and a third enriched with carbon-13. Samples were cooled to below 4 Kelvin to isolate quantum effects.

Findings and Impact

Using photoluminescence spectroscopy and Fourier transform infrared spectrometry, the team identified that replacing hydrogen with deuterium lowered the energy of the carbon-hydrogen (C–H) bond vibration. This reduction in vibrational energy suppresses the nonradiative decay pathway, leading to more efficient light emission.

Measurements of excited-state lifetime using pulsed resonant laser excitation showed that the deuterated T center's lifetime was 5.4 times longer than that of the protium version. Initial estimates suggest the deuterated T center could achieve efficiencies exceeding 90%, possibly reaching over 98%. This phenomenon was termed a "giant isotope effect," indicating a strong link between energy loss and local C–H bond vibrations. Modeling corroborated that considering only the C-H stretch mode accurately reflects the strong isotope dependence.

The heavier isotope also improved "optical cyclicity," allowing the system to be excited and emit light approximately 300 times more often than the protium version before needing a reset.

This improvement makes single-shot readout of the electron spin feasible and could accelerate quantum operations on T centers.

Future Outlook

This research challenges the previous perception of silicon color centers as inefficient compared to defects in materials like diamond, providing evidence that silicon can host highly efficient single-photon emitters. The inherent emission of T centers in the telecom O-band makes them suitable for distributing quantum information across existing optical fiber infrastructure. Photonic Inc. has reportedly begun integrating the deuterated T center into its development process.

Further research is planned to comprehensively study the fundamental vibrational modes across all possible isotopic variants of the T center to understand how its vibrational structure affects optical properties.