Integrated quantum photonics
The nano-optics section focusses its research on wavelength-scale structures to control photon propagation and the interaction of photons with electronic excitations and spins in semiconductor quantum dots. The principal long term goal is the integration of such functions to achieve the first Semiconductor Integrated Quantum Optical Circuits. Both photonic crystals and suspended nanobeam structures are employed to guide and control the photon propagation. Cavities also play a key role, to enable the regime of cavity quantum electrodynamics to be attained.
The research is carried in well-equipped laboratories, with a variety of continuous wave and ultrafast lasers, highly stable low temperature optical systems and high resolution spectrometers all available. We have access to excellent fabrication facilities in the EPSRC National Epitaxy Facility in Sheffield, where we fabricate our structures using high resolution electron beam lithography and reactive ion etching techniques.
A semiconductor topological photonic ring resonator
Topological insulators are fermionic systems in which the bulk material is insulating, but conduction is nevertheless possible due to the presence at the surface of topologically-protected edge states (see the quantum Hall effect for a famous example). Recently, a bosonic analogy – topological photonics – has become a new paradigm in nano-photonics research. Of particular interest is the possibility of topologically-protected optical waveguiding in nano-photonic structures, with the potential for very low-loss light transmission, protected against backscatter. Here, we demonstrate the operation of a micron-scale photonic ring resonator in GaAs, formed using a quantum spin Hall-type topological photonic crystal membrane. We use embedded InGaAs quantum dots to generate an internal white-light probe for the resonator modes, and show how the transverse confinement of the modes can be tuned via the photonic crystal lattice parameters.
Further reading: Appl. Phys. Lett. 116 061102 (2020)
Manipulating photon statistics of light on-chip using Fano interference
Quantum light is a fundamental resource for quantum photonic technologies. Here, we convert a classical coherent laser into either bunched or anti-bunched (non-classical) light on-chip. We embed a single QD in a nano-photonic waveguide in which back reflections (from the waveguide terminations) lead to Fabry-Perot resonances. The phase of light in the waveguide/weak cavity is then used as a tool to control quantum interference when single photons scatter from the QD. We show that by varying the detuning of a weak coherent laser injected into the waveguide relative to the QD exciton transition, the transmitted light can be tuned from bunched, to coherent, to antibunched. This is in contrast to the case of an ideal waveguide without back reflections, in which the transmitted light can only be bunched.
Further reading: Phys. Rev. Lett. 122 173603 (2019)
Electrically-tunable photon-photon interactions
Light is an almost ideal information carrier with a very long coherence time, and is therefore of great interest for quantum computation. However, this comes at the cost of intrinsically weak photon-photon interactions, which are necessary for the deterministic operation of quantum photonic gates. One technique to address this challenge is to leverage an intermediary element which can enable an effective photon-photon interaction. Here, we couple a single QD to the single optical mode of a waveguide, and demonstrate that the QD acts as such an intermediary. We show that this effect can be tuned by electrically controlling the QD, allowing future scale-up of the device to multiple QDs.
Further reading: Optica 5(5) 644-650 (2018)