Event
Ph.D. Research Proposal Exam: Amirehsan Alizadehherfati
Monday, November 30, 2026
3:00 p.m.
AVW 2328
ANNOUNCEMENT: Ph.D. Research Proposal Exam
Name: Amirehsan Alizadehherfati
Committee:
Professor Edo Waks (Chair)
Professor Saikat Guha
Professor Ronald Walsworth,
Date/time: November 30 at 3:00 PM
Location: AVW 2328 (ECE)
Title: The Al-C Center as a Bright Telecom Spin–Photon Interface in Silicon
Abstract: Optically addressable solid-state spins provide the stationary memory that quantum networks connect through photons, and in the past decade, silicon has emerged as the unmatched foundation for the integrated photonics such networks require. However, the field still lacks a viable defect capable of simultaneously meeting the optical, coherence, and spin requirements necessary for scalable processors linked by telecom-band photonic qubits. While the well-known T-center proved that silicon could host an accessible spin memory, its microsecond radiative lifetime and thermally fragile excited state limit its photon rate and optical coherence.
This proposal develops the Al-C center, an aluminum–carbon defect in silicon, as a spin–photon interface that retains the advantages of the T-center while removing both limitations. In recent work I co-led, we demonstrated waveguide-integrated, high-purity single-photon emission from individual Al-C centers with a 135 ns excited-state lifetime, an order of magnitude shorter than that of the T-center, and twentyfold higher brightness in identical devices. Their homogeneous linewidth of about 20 MHz lies within a factor of about twenty of the lifetime limit and remains narrow up to 6 K. Magneto-optical spectroscopy resolved all four spin-dependent transitions, and time-resolved measurements demonstrated spin-selective optical pumping and determined the cyclicity and spin relaxation time.
However, coherent control of the spin remains unexplored, the measured single-center resonance spans a 10.85 GHz spectral-diffusion envelope, and coupling to nuclear spins or cavities has not been established. The proposed research addresses these gaps in four aims. Aim 1 establishes ensemble microwave control through spectral holes and antiholes and benchmarks the spin properties against the T-center. Aim 2 investigates high-temperature annealing and electron irradiation to separate lattice repair from Al-C formation and narrow the optical line. Aim 3 develops the intrinsic ²⁷Al nucleus and isotope-engineered ¹³C into a local nuclear spin register. Aim 4 couples single centers to photonic crystal cavities to enhance emission and pursue high-visibility photon interference and spin–photon entanglement.
Together, these efforts will advance the Al-C center from a bright telecom emitter toward a coherently controlled spin–photon interface for silicon-based quantum networks.
