Colloquia

Title: Engineering and Controlling Semiconductor Spin Qubits with Light

Abstract

Semiconductor quantum dots provide a solid-state platform for optically addressable spin qubits, combining confined electronic states with direct optical access and compatibility with semiconductor nanophotonic structures. Their development for quantum technologies requires reliable methods for spin preparation, coherent control and readout, as well as approaches that improve the reproducibility and positioning of individual quantum emitters.

Recent work from the Experimental Quantum Nanoscience Lab at the University of Strathclyde has investigated optical control of individual spins in semiconductor quantum dots. In self-assembled InAs quantum dots, an unconventional magnetic-field geometry is used in which the field is applied at an oblique angle to the quantum-dot growth axis. This allows the ground-state spin eigenstates and optical selection rules to be tuned between the conventional Faraday and Voigt configurations. Using this geometry, optical spin initialization and ultrafast coherent control of the electron spin have been demonstrated, including control of both the population and phase of the spin state. Ongoing work extends these experiments to multi-pulse coherent-control sequences, including the implementation of composite π-rotations under oblique magnetic fields.

A complementary research direction, carried out in collaboration with Tyndall National Institute, investigates site-controlled InGaAs pyramidal quantum dots. These structures offer deterministic spatial positioning and therefore provide an alternative to randomly nucleated self-assembled quantum dots. Experiments on charged pyramidal dots have demonstrated optical spin pumping and initialization, together with ultrafast coherent control of the optical transition, establishing several of the ingredients required for further investigation of spin control in site-controlled quantum-dot systems.

Together, these studies explore how magnetic-field geometry, optical excitation and quantum-dot design can be used to control quantum states in semiconductor nanostructures, with the broader aim of developing optically addressable solid-state systems for quantum technologies.

Selected references

[1] K. Barr et al., Phys. Rev. B 109, 075433 (2024).

[2] I. Samaras et al., Quantum Sci. Technol., in press (2026).

[3] R. A. Barcan et al., Phys. Rev. B 112, L121301 (2025).

[4] R. A. Barcan et al., Sci. Rep. 16, 4114 (2026).

Short biography

Konstantinos G. Lagoudakis is a Reader (Associate Professor) in Physics at the University of Strathclyde and leads the Experimental Quantum Nanoscience Lab. His research spans quantum nanophotonics, semiconductor spin qubits and strongly coupled light–matter systems, with a particular focus on the optical control of quantum states in nanoscale solid-state platforms. During his PhD at EPFL, he made key contributions to the study of exciton–polariton condensates, including work on quantized and half-quantum vortices. He subsequently moved to Stanford University, where he worked on coherent control and spin–photon interfaces in semiconductor quantum dots and diamond colour centres. At Strathclyde, his group is developing new approaches to spin-qubit control, scalable quantum-dot platforms and hybrid photonic systems aimed at future quantum technologies.