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Title: Some aspects of measurement of quantum systems
Author: Colin, Andrew
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2012
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This thesis is about two different aspects of measurement. The first aspect concerns programmed discrimination, where a single binary digit is coded in the relationship between three qbits. There are two different 'program' qbits, and a 'data' qbit which is guaranteed to be identical to one or other of the program qbits. The task of programmed discrimination is to discover, as accurately as possible, which of the two possibilities is true. Most prior work assumes that the two program qbits are randomly placed on the surface of the Bloch sphere. Our own research examines error and failure rates when there is some classical information about the two program qbits. We considered three configurations: There is a known overlap between the program qbits; Both program qbits are on a known great circle; The program qbits are confined to polar caps of a known size. Our results cover both error rates in optimum recognition and failure rates in unambiguous discrimination, and consider the effe cts of using multiple copies of the qbits. The second aspect studies the effects of frequent, but possibly incorrect, measurement on otherwise closed quantum systems with two eigenstates. Previous work has set up a model for this situation, and showed the existence of 'telegraphing', in which the state of the system changes very little over extended periods of time before switching to the opposite state. This is related to the Zeno 1 effect, whereby a system that is measured repeatedly at frequent intervals does not change state. Our work offers a mathematical analysis of the situation, and shows that the analysis conforms well to practical results obtained from a simulator. The overall arrangement of the thesis is: Chapter 1: A general introduction to relevant areas of quantum physics; Chapter 2: A review of previous work in programmed discrimination; Chapters 3 and 4: Reports on our own research in programmed discrimination; Chapter 5: A summary of a recent paper on telegraphing; Chapter 6: Our work on telegraphing; Chapter 7: Conclusion. Our original work is presented in Chapters 3, 4 and 6.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available