第6.7回 物理工学科教室談話会（講師：Prof. L.P. Kouwenhoven/Prof. D. Loss）
Prof. L.P. Kouwenhoven (Delft Univerity of Technology, The Netherlands)
Majorana Fermions, from particle physics on a chip to topological quantum computing
Majoranas can emerge as robust quasi-particles in properly engineered electronics devices. The needed ingredients include low-dimensional semiconductors with strong spin-orbit interaction and superconductivity.
Within appropriate ranges of magnetic field and chemical potential a spin-less and charge-less quantum state emerges that is firmly pinned at zero energy. This zero energy state has all the experimental signatures of a Majorana bound state. Majoranas become particularly interesting when we can operate them as qubits since these are expected to be protected against many noise sources. This protection has a topological origin which persists as long as the global parity (i.e. even or odd total particle number) in the sample remains fixed. We have observed parity lifetimes of order a minute.
Current research is developing superconducting circuits that allow for Majorana qubit operations. These operations involve braiding Majoranas, or exchanging pairs of Majoranas, which should demonstrate that their quantum statistics is non-Abelian.
Prof. D. Loss (University of Basel, Switzerland and RIKEN Center for Emergent Matter Science)
From Majorana- to Para-Fermions in Nanowires and Atomic Chains
要旨：I will present recent theoretical results on exotic bound states which can emerge in lower dimensions in the presence of spin orbit interaction or spatially periodic magnetic fields, and in RKKY systems forming intrinsic spin helices. I will discuss candidate materials such as semiconducting Rashba nanowires and atomic magnetic chains. Examples of such bound states are fractionally charged fermions, Majorana fermions, and, in particular, parafermions whose braiding statistics enables entanglement (in contrast to Majoranas). I will mention recent progress on error correction for topological quantum computation.