[quantum-info] Colloquium Institute for Quantum Computing Monday, 21 October

[Matthew Fries]

Colloquium

Institute for Quantum Computing

Monday, 21 October 2013 at 2:30PM

QNC 0101

Coherent electronic states in semiconductor nanowires: flux quantization, and proximity-effect superconductivity

Jonathan Baugh

Institute for Quantum Computing

Nanotechnology is continually providing new materials to explore for use in future classical and quantum devices. We have recently investigated low temperature electronic transport in various device configurations based on InAs nanowires. In a simple field-effect transistor geometry, magnetoconductance experiments on core-shell nanowires reveal phase coherent electronic states. In particular, oscillations in axial-field magnetoconductance with periodicity corresponding to the flux quantum are a signature of coherent 'ring' states around the wire circumference, owing to a surface accumulation layer of electrons [1]. These results suggest a high degree of structural order, i.e. that properly tailored nanowires can serve as a reasonably clean system for a variety of quantum transport experiments. Secondly, motivated by the recent search for topological states in semiconductor-superconductor heterostructures, we have investigated a nanowire in the quasi-ballistic regime contacted with a type-II superconductor, Niobium. A supercurrent is observed in this junction below a critical current of up to 40 nA; the critical current varies with local gating in proportion to the normal state conductance. Detailed analysis of a wide range of data from this device reveals certain features that are expected for SNS junctions, and some that are as yet puzzling, and may be related to the quasi-1D nature of the nanowire. I will discuss these results in the light of potential quantum device applications. [1] http://lanl.arxiv.org/abs/1305.5552