Past Quantum Field Theory Seminar

21 May 2013
12:00
Ivette Fuentes (Nottingham)
Abstract
Cutting-edge experiments in quantum communications are reaching regimes where relativistic effects can no longer be neglected. For example, there are advanced plans to use satellites to implement teleportation and quantum cryptographic protocols. Relativistic effects can be expected at these regimes: the Global Positioning System (GPS), which is a system of satellites that is used for time dissemination and navigation, requires relativistic corrections to determine time and positions accurately. Therefore, it is timely to understand what are the effects of gravity and motion on entanglement and other quantum properties exploited in quantum information. In this talk I will show that entanglement can be created or degraded by gravity and non-uniform motion. While relativistic effects can degrade the efficiency of teleportation between moving observers, the effects can also be exploited in quantum information. I will show that the relativistic motion of a quantum system can be used to perform quantum gates. Our results, which will inform future space-based experiments, can be demonstrated in table-top experiments using superconducting circuits.
  • Quantum Field Theory Seminar
23 April 2013
12:00
Philip Stamp (Vancouver)
Abstract
              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

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