Past Quantum Field Theory Seminar

23 April 2013
Philip Stamp (Vancouver)
              Conventional decoherence (usually called 'Environmental Decoherence') is supposed to be a result of correlations established between some quantum system and the environment. 'Intrinsic decoherence' is hypothesized as being an essential feature of Nature - its existence would entail a breakdown of quantum mechanics. A specific mechanism of some interest is 'gravitational decoherence', whereby gravity causes intrinsic decoherence. I will begin by discussing what is now known about the mechanisms of environmental decoherence, noting in particular that they can and do involve decoherence without dissipation (ie., pure phase decoherence). I will then briefly review the fundamental conflict between Quantum Mechanics and General Relativity, and several arguments that suggest how this might be resolved by the existence of some sort of 'gravitational decoherence'.  I then outline a theory of gravitational decoherence (the 'GR-Psi' theory) which attempts to give a quantitative discussion of gravitational decoherence, and which makes predictions for experiments. The weak field regime of this theory (relevant to experimental predictions) is discussed in detail, along with a more speculative discussion of the strong field regime.
  • Quantum Field Theory Seminar
15 January 2013
Mir Faizal
We will first review the construction of N =1 supersymmetric Yang-Mills theory in three dimensions. Then we will construct a superloop space formulation for this super-Yang-Mills theory in three dimensions.Thus, we will obtain expressions for loop connection and loop curvature in this superloop space. We will also show that curvature will vanish, unless there is a monopole in the spacetime. We will also construct a quantity which will give the monopole charge in this formalism. Finally, we will show how these results hold even in case of deformed superspace.
  • Quantum Field Theory Seminar
30 October 2012
Alastair Kay

Topological quantum error correcting codes, such as the Toric code, are
ideal candidates for protecting a logical quantum bit against local noise.
How are we to get the best performance from these codes when an unknown
local perturbation is applied? This talk will discuss how knowledge, or lack
thereof, about the error affects the error correcting threshold, and how
thresholds can be improved by introducing randomness to the system. These
studies are directed at trying to understand how quantum information can be
encoded and passively protected in order to maximise the span of time between successive rounds of error correction, and what properties are
required of a topological system to induce a survival time that grows
sufficiently rapidly with system size. The talk is based on the following
papers: arXiv:1208.4924 and Phys. Rev. Lett. 107, 270502 (2011).

  • Quantum Field Theory Seminar