EPSRC Programme Grant 2016-2021

Semiconductor Quantum Photonics: Control of Spin, Exciton and Photon Interactions by Nano-Photonic Design

This grant exploits the advantageous properties of III-V semiconductors to achieve agenda setting advances in the quantum science and technology of solid state materials. We work in the regime of next generation quantum effects such as superposition and entanglement, where III-V systems have many favourable attributes, including strong interaction with light, picosecond control times, and microsecond coherence times. The grant is a collaboration between the Universities of Sheffield, Cambridge (D A Ritchie) and Lancaster (H Schomerus), capitalising on the advanced, complementary expertise in each institution.

We employ the principles of nano-photonic design to access new regimes of physics and potential long term applications. Many of these opportunities have only opened up in the last few years, due to conceptual and fabrication advances. The conceptual advances include the realisation that quantum emitters emit only in one direction if precisely positioned in an optical field, that wavepackets which propagate without scattering may be achieved by specific design of lattices, and that non-linearities are achievable at the level of one photon. The fabrication advances allow reconfigurable devices to be realised, with on-chip control of electronic and photonic properties.

Key goals include reconfigurable devices at the single photon level, a single photon logic gate based on the fully confined states in quantum dots positioned precisely in nano-photonic structures, and coupling of states by designed optical fields, taking advantage of the reconfigurable capability, to enhance or suppress optical processes. We plan to achieve spins connected together by photons in an on-chip geometry, a route towards a quantum network.

As well as quantum dots, III-V quantum wells interact strongly with light to form new particles termed polaritons. We propose to exploit the new field of topological polaritonics, where the nano-photonic design of lattices leads to states which are protected from scattering and where artificial magnetic fields are generated. This opens the way to new coupled states of matter which mimic the quantised Hall effects, but in a system with fundamentally different wavefunctions from electrons.

SEM image of  proof-of-concept micro-opto-electromechanical comb-drive actuated structure. An applied voltage is applied to vary the gap between the directional coupler waveguides (arrow in (b)).

SEM image of proof-of-concept micro-opto-electromechanical comb-drive actuated structure. An applied voltage is applied to vary the gap between the directional coupler waveguides (arrow in (b)).

Finally, our programme also depends on excellent crystal growth. We target one of the main issues limiting long term scale up of quantum dot technologies, namely site control. We will employ two approaches, which involve a combination of patterning, cleaning and crystal growth to define precisely the quantum dot location, both based around the formation of pits to seed growth in predetermined locations.

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