Quantum materials
A fundamental building block of quantum technologies are the materials used. To exploit quantum phenomena we need materials that allow us to access and precisely control individual particles, such as electrons and protons, at the quantum level.
III-V semiconductors
Our research in quantum science and technology is largely carried in the III-V semiconductor family of materials. Much of the physics and technologies outcomes are described in the Quantum light section.
The University of Sheffield is very well placed to achieve high impact in this area through its hosting of the National Epitaxy Facility for III-V materials crystal growth, which feeds into our wide-ranging physics and technology activities.
Much of our work is based on semiconductor quantum dots, nanometre scale islands with very strong confinement which exhibit single photon emission with nearly ideal radiative and decoherence properties.
Our research covers a wide range of wavelengths including 900nm, 1.3μm and 1.55μm which all exhibit high quality single photon emission. This has enabled a series of quantum physics and technology publications described in the Quantum light section, including:
Optica, 5(5) 644-650 (2018) (900 nm)
Science, 364, 62, (2019) (900 nm)
Nature Communications, 9, 862 (2018) (1.55 μm)
A typical transmission electron microscope image of a quantum emitter.
Facilities
The state of the art quantum dots are grown by molecular beam epitaxy (MBE) (900nm) and metalorganic chemical vapour deposition (MOCVD) (1.55μm) in the National Epitaxy Facility. Overall the facility has three MBE and three MOCVD reactors dedicated to the growth of advanced electronic materials.
We employ a typical MBE machine to grow most of our quantum dot structures. Our most advanced epitaxy machine, commissioned in summer 2019 for quantum dot growth, is a three chamber ‘cluster’ tool funded by the UK National Quantum Technology programme. It is specially designed to achieve site control of quantum dot growth, a key factor to achieve scalability of the technology in the coming years.
As well as the wide ranging epitaxy facilities, we are very well equipped for device fabrication to achieve quantum circuit functions of the type realised in the Quantum light section.
Our equipment includes electron beam lithography, two inductively coupled plasma (ICP) etching machines, ICP-PECVD for dielectric deposition and plasma ashing. The crystal growth and device fabrication equipment is housed in modern 500 m² clean rooms, enabling both growth and fabrication in highly favourable conditions.
Lead researchers
Ian Farrer, Jon Heffernan, Edmund Clarke.
MBE machine used to grow most of our quantum dot structures.
Advanced epitaxy machine, commissioned in 2019.
2D materials
Hundreds of two-dimensional (2D) graphene-like atomically thin crystals are a new type of quantum nano-materials. They provide unprecedented versatility for how a new meta-material or a nanoscale device can be designed and created. We work on unravelling this potential by studying how such materials and artificial stacks of atomic 2D layers (so-called van der Waals heterostructures) interact with light.
Highlights
We have discovered that when two atomically thin graphene-like materials are placed on top of each other their properties change, and a material with novel hybrid properties emerges. This happens without physically mixing the two atomic layers, not through a chemical reaction, but just by attaching the layers to each other via weak van der Waals interaction, similar to how a sticky tape attaches to a flat surface.
This novel quantum phenomenon opens unprecedented control on the design of novel quantum nano-materials.
We have discovered the strong light-matter interaction regime within an atomically thin 2D monolayer semiconductor placed in a tunable optical microcavity. We have observed that the bound electron and hole pairs called excitons strongly interact with the microcavity photonic mode to form a new type of a quasi-particle called polariton.
Polaritons are expected to open the way to very strong optical non-linearities, and allow control of light with low-intensity light on ultra-fast time-scales.
Nature Communications, 6, 8579 (2015)
We have discovered that the part-light part-matter polaritons in 2D semiconductors transition metal dichalcogenides (TMDs) provide additional protection to the quantum degrees of freedom inherent to excitons in TMDs.
So-called valley pseudo-spin and its coherence have been found to be enhanced when excitons in a TMD monolayer are coupled to a microcavity photonic mode.
Nature Photonics, 11, 497 (2017)
Nature Communications, 9, 4797 (2018)
Lead researcher
Alexander Tartakovskii.
