This CDT project develops a 4H-SiC integrated platform for spin–photon interfaces and on-chip single-photon detection, providing key building blocks for the implementation of scalable
quantum repeaters.
4H-SiC hosts colour centres that act as artificial atoms. These spin-active centres can be created by electron-beam irradiation and annealing. For example, the electron-spin confined in a SiC silicon-vacancy has been demonstrated as a room-temperature, bright dipole-emission qubit, with optical initialisation/readout and microwave coherent control. To bring this system closer to applications, the project addresses the 4H-SiC platform from the points of scalability (deterministic coupling) and device interface (chip-integration with SNSPDs).
The primary supervisor (PS) has an internationally recognised track record in semiconductor cavity QED [1]. The work builds on two funded programmes currently ongoing in the PS’s lab at UofG: (i) high Q/V 4H-SiC nanocavities (Royal Society Fellowship) and (ii) fabrication of 4H-SiC thin-film-on-insulator (EPSRC-PQA).
Scientific Objectives
1. Demonstrate Purcell-enhanced emission of SiC colour centres deterministically coupled to photonic crystal nanocavity (PCN) modes. PCNs designed by in-house developed machine-learning-guided inverse design. Tuning of cavity/emitter emissions by digital etch [2] and in-situ controlled condensation [3] by a specially designed cryostat. Spatial nanopositioning [4]. Spectroscopy by µ-PL, cross-polarisation resonant scattering and photon correlation measurements.
Key Challenges: Precise spatial/spectral alignment of emitters and cavity; spectral diffusion and pure dephasing; yield of high-brightness centres.
Mitigation/contingency: If yield limits progress, deploy shallow-implant arrays to raise coupling probability. Leverage Attocube facilities (cryostat maker) to improve condensation tuning and the
optical nanopositioning implemented in the cryostat.
2. Increase Q/V to access a deterministic strong coupling regime and enable coherent state exchange between a colour centre spin and a cavity photon. Inverse-designed/ML-optimised PCNs with fabrication tolerance-aware objectives.
Key Challenges: Achieving Q > 5×10⁴ in SiC with reproducibility; electron–phonon coupling that reduces effective g; dephasing under resonant drive.
Mitigation/contingency: Leverage in-kind by RENA Technology to improve etching. If single emitter coupling is insufficient, transition to collectively enhanced coupling with small ensembles (boosting effective g as gₑff ≈ g√N), or pivot to a high-Purcell-enhanced regime for fast, high-fidelity spin readout so that O3 can start.
3. Implement on-chip photon routing/demultiplexing co-integrated with SNSPDs, with a path t photon-number resolution, to form an optical quantum interconnect primitive.
Key Challenges: Coupling/insertion losses across interfaces; fabrication tolerances; detector timing jitter/dark counts; cryogenic integration complexity.
Mitigation/contingency: Tolerance-aware ML design embedding fabrication spreads; adiabatic mode converters and critically coupled cavity–nanowire interfaces for near-unity absorption. If on-chip efficiency initially falls short, use hybrid packaging with off-chip SNSPDs and external demultiplexers as an interim step while iterating to full integration.
Outcomes & Training
The project is ambitious yet de-risked through defined mitigations anchored in ongoing, funded programmes. It can deliver SiC building blocks—deterministic single-photon sources, spin-photon
interfaces, and integrated single-photon detection—constituting a chip-level interconnect acting as quantum links. The doctoral researcher will gain end-to-end skills in nanofabrication, spectroscopy, ML-assisted photonic design, cryogenic measurements, nanopositioning, and systems-level integration, aligning them to lead the next generation of scalable quantum hardware