Seminar

Abstract

A welded tree is a graph consisting of two binary trees "welded"
together with a random cycle between the leaves. In 2003, Childs et
al. showed that a quantum walk has an exponential speedup over
classical algorithms when traversing the graph from one root vertex to
the other. I give evidence that related graphs also have an
exponential gap between classical algorithms and the quantum walk.

David Gosset, Institute for Quantum Computing (IQC)

Pragya Shukla, Indian Institute of Technology Kharagpur

Abstract

We provide the first two-party protocol allowing Alice and Bob to evaluate privately even against active adversaries a completely positive, trace-preserving map F, given as a quantum circuit, upon their joint quantum input state. Our protocol leaks no more to any active adversary than an ideal functionality for F provided Alice and Bob have the cryptographic resources for active secure two-party classical computation.

Helen Fay Dowker, Imperial College London

Abstract

Slow neutrons are used in a very broad spectrum of scientific investigations. I will discuss how neutrons are liberated from nuclei and lowered in energy to regimes of interest. I will also discuss some examples of experiments, mainly motivated by questions in nuclear/particle/astrophysics.

Aashish Clerk, McGill University

Abstract

Evidence is presented for the finite wave vector crossing of the two lowest one-dimensional spin-split subbands in quantum point contacts fabricated from two-dimensional hole gases with strong spin-orbit interaction. This phenomenon offers an elegant explanation for the anomalous sign of the spin polarization filtered by a point contact, as observed in magnetic focusing experiments. Anticrossing is introduced by a magnetic field parallel to the channel or an asymmetric potential transverse to it.