PHYSICS COLLOQUIUM The College of William and Mary Time: Friday November 12 2010, 4:00 PM. Location: Millington Hall 150 Sankar Das Sarma

Condensed Matter Theory Center, University of Maryland

Computing with Quantum Knots: Majorana Fermions, Non-Abelian Anyons, and Topological Quantum Computation

Abstract

I will discuss the revolutionary new concept of topological quantum computation, which is fault- tolerant at the hardware level with no need, in principle, of any quantum error correction protocols. Errors simply do not happen since the physical and the computation steps are protected against decoherence by non-local topological correlations in the underlying physical system. The key idea is non-Abelian statistics of the (called 'anyons' as opposed to fermions or bosons), where the space-time braiding of the anyons around each other, i.e. quantum 'knots', form topologically protected quantum gate operations. I will describe in detail the status of the subject by discussing the theoretical principles guiding the experimental search for the appropriate topological phases of matter where such non-Abelian anyons may exist. Among the most significant possibilities are certain even-denominator fractional quantum Hall states, exotic chiral p-wave superconductors, sandwich structures made from superconductors/ or superconductors/insulators, and suitably designed cold atomic systems. In this context, I will also discuss the race to find Majorana fermions in solid state systems, with the Majorana fermions being the simplest generic examples of non-Abelian objects in nature. I will explain how the subject of topological quantum computation synergistically brings together conformal field theory and advanced mathematics on one hand with materials science and on the other.

About the Speaker

Sankar Das Sarma is the Richard E. Prange Chair in Physics & Distinguished University Professor & Director of Condensed Matter Theory Center at the University of Maryland, College Park. He has coauthored more than 400 scholarly articles. His highly cited work (currently collecting more than 22,000 citations) spans from the physics of electrons in low dimensions, to the , Quantum Computation, Topological Quantum Computation, Spintronics, and Cold Atoms. He is the editor of the book Perspectives in Quantum Hall Effects and of several well-known review articles. The Condensed Matter Theory Center that he founded in 2002 and of which he is the permanent director, currently employs 15 Postdoctoral Associates and several graduate students.