Optical observation of single spins in silicon

The article presents a breakthrough in the optical detection of individual spins in silicon, which is crucial for the development of scalable quantum information networks. It demonstrates the integration of silicon-based T center photon-spin qubits in photonic devices, marking a significant step towards building telecommunications-band, silicon-integrated quantum systems.

Key Findings:

1. T Center Characteristics:

• The T center in silicon is a radiation damage center consisting of two carbon atoms, one hydrogen atom, and an unpaired electron. It features a zero-phonon line (ZPL) transition at 935.1 meV, in the near-infrared telecommunications band.

• The T center’s electron spin and nuclear spin are long-lived, with coherence times exceeding 2 ms for the electron and 1.1 s for the hydrogen nucleus in isotopically pure silicon.

2. Photon-Spin Interface:

• The T center offers a photon-spin interface with spin-dependent optical transitions in the telecommunications band. The transitions are fine-tuned by a static magnetic field, and the spins can be optically initialized and measured.

• The team used a custom-built cryogenic confocal microscope to resolve individual T centers and measure their spin-dependent optical transitions.

3. Fabrication of Micropucks:

• The study involved generating tens of thousands of silicon photonic devices by embedding T centers in micropucks on standard silicon-on-insulator (SOI) wafers. These devices enhance the coupling efficiency and optical collection by increasing the out-coupling of light through Purcell enhancement.

4. Resonant Excitation and Spectroscopy:

• Single T centers were optically addressed using resonant excitation. The linewidths of individual T center transitions were measured to be significantly narrower than the inhomogeneously broadened ensemble, with some centers exhibiting linewidths 40 times narrower.

5. Single Spin Detection:

• The article reports the successful optical initialization and readout of single electron spins in silicon. Using two-color resonant excitation spectroscopy, the researchers resolved spin-selective transitions and measured spin lifetimes.

• Spin lifetime measurements showed that the T centers can maintain coherent spin states over long timescales, which is essential for quantum information processing.

6. Autocorrelation and Single-Photon Emission:

• The Hanbury Brown-Twiss measurement confirmed the single-photon nature of the emission from individual T centers. The background-subtracted autocorrelation function yielded a g2(0) value of 0.20(6), indicating single-spin behavior and confirming the feasibility of using these centers for quantum technologies.

7. Future Applications:

• These silicon T centers, with their long spin coherence times and efficient optical transitions, are well-suited for integration into scalable quantum networks. With further development, they could serve as building blocks for telecommunications-linked quantum communication and computing systems.

Conclusion:

This work represents a significant advancement in the development of silicon-based quantum technologies. By integrating T center spin qubits into photonic structures, the authors have demonstrated that silicon can serve as a platform for scalable, telecommunications-band quantum networks, pushing the field closer to realizing practical quantum communication systems.