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Title: Gaussian non-classical correlations in bipartite dissipative continuous variable quantum systems
Author: Quinn, Niall
ISNI:       0000 0004 5364 8126
Awarding Body: University of St Andrews
Current Institution: University of St Andrews
Date of Award: 2015
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This thesis probes the usefulness of non-classical correlations within imperfect continuous variable decoherent quantum systems. Although a consistent function and practical usefulness of these correlations is largely unknown, it is important to examine their characteristics in more realistic dissipative systems, to gain further insight into any possible advantageous behaviour. A bipartite separable discordant state under the action of controlled loss on one subsystem was considered. Under these conditions the Gaussian quantum discord not only proved to be robust against loss, but actually improves as loss is intensified. Harmful imperfections which reduce the achievable level of discord can be counteracted by this controlled loss. Through a purification an explanation of this effect was sought by considering system-environment correlations, and found that a flow of system-environment correlations increases the quantumness of the state. Entanglement recovery possibilities were discussed and revealed the importance of hidden quantum correlations along bi-partitions across the discordant state and a classically prepared "demodulating" system, acting in such a way as to partially cancel the entanglement preventing noise. Entanglement distribution by separable states was studied by a similar framework, in an attempt to explain the emergence of quantum entanglement by a specific flow of correlations in the globally pure system. Discord appears to play a less fundamental role compared to the qubit version of the protocol. The strengthening of non-classical correlations can be attributed to a flow of classical and quantum correlations. This work proves that discord can be created in unique ways and, in select circumstances, can act to counteract harmful imperfections in the apparatus. Due to this advantageous behaviour discord indeed may ultimately aid in more applicable "real world" applications, which are by definition decoherent.
Supervisor: Korolkova, Natalia Sponsor: Engineering and Physical Sciences Research Council (EPSRC)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Quantum information ; Quantum communication ; Entanglement ; Discord ; Non-classical ; Quantum optics ; Gaussian states ; Decoherence ; QC174.13Q5 ; Quantum systems ; Quantum entanglement ; Quantum optics