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.
Below we detail some of our activities in this area:
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 of the Research tab on the web site. 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 (http://www.nationalepitaxyfacility.co.uk/), which feeds into our wide-ranging physics and technology activities (https://ldsd.group.shef.ac.uk/).
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. A typical transmission electron microscope image of such a quantum emitter is shown above.
Our research covers a wide range of wavelengths including 900 nm, 1.3 μm and 1.55 μm 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 of this web site, including Nature Nanotechnology 13, 835–840 (2018) (900 nm), Optica 5(5) 644-650 (2018) (900 nm), Science 364, 62, (2019) (900 nm), Nature Communications 9, 862 (2018) (1.55 μm). A fuller listing may be found at https://ldsd.group.shef.ac.uk/publications/.
The state of the art quantum dots are grown by molecular beam epitaxy (MBE) (900 nm) and metalorganic chemical vapour deposition (MOCVD) (1.55 μm) in the National Epitaxy Facility. Overall the facility has 3 MBE and 3 MOCVD reactors dedicated to the growth of advanced electronic materials. A typical MBE machine employed to grow most of our quantum dot structures is shown on the left below. 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, shown on the right below. 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, and as shown for example in the figure to the right. 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.
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, no 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 open unprecedented control on the design of novel quantum nano-materials. (Nature 567, 81 (2019))
- 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))