Contents

Departments

Theoretical Physics in Sheffield

Colloquia and Seminars

29 November 2011 The Maggot in the apple: peaceful coexistence of incompatible theories
Sir Michael Berry FRS, University of Bristol
5pm, LT6, Hicks building
In physics, as in science generally, most phenomena can be understood in more than one way: the gas in an engine obeys not only the laws of thermodynamics but also those of the motion of its molecules. The different theories correspond to different levels of description. These must overlap, but their consilience is far from straightforward because they seem based on incompatible concepts. The discordance arises from the fact, appreciated in its generality only recently, that the limit in which the more encompassing theory reduces to the less general (usually older) theory is mathematically singular. One consequence is a range of phenomena, of intense current interest, inhabiting the borderlands between the theories. I will explore this theme with examples from the physics of fluids, light and the quantum world.
14 December 2011 Effective horizons for quantum communication in a Schwarzschild spacetime
Dominic Hosler, University of Sheffield
Nottingham University
Communication between a free-falling observer and an observer hovering above the Schwarzschild horizon of a black hole suffers from Unruh-Hawking noise, which degrades communication channel capacities. Ignoring time dilation, which affects all channels equally, we show that for bosonic communication using single and dual rail encoding the classical channel capacity reaches a finite value and the quantum channel capacity falls off exponentially. The latter defines an effective horizon, beyond which quantum communication becomes exponentially resource inefficient. The characteristic length scale associated with this quantum horizon depends on the mass of the black hole and the frequency of the communication channel.