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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Welch Bounds and Quantum State Tomography

Belovs, Aleksandrs January 2008 (has links)
In this thesis we investigate complete systems of MUBs and SIC-POVMs. These are highly symmetric sets of vectors in Hilbert space, interesting because of their applications in quantum tomography, quantum cryptography and other areas. It is known that these objects form complex projective 2-designs, that is, they satisfy Welch bounds for k = 2 with equality. Using this fact, we derive a necessary and sufficient condition for a set of vectors to be a complete system of MUBs or a SIC-POVM. This condition uses the orthonormality of a specific set of vectors. Then we define homogeneous systems, as a special case of systems of vectors for which the condition takes an especially elegant form. We show how known results and some new results naturally follow from this construction.
2

Welch Bounds and Quantum State Tomography

Belovs, Aleksandrs January 2008 (has links)
In this thesis we investigate complete systems of MUBs and SIC-POVMs. These are highly symmetric sets of vectors in Hilbert space, interesting because of their applications in quantum tomography, quantum cryptography and other areas. It is known that these objects form complex projective 2-designs, that is, they satisfy Welch bounds for k = 2 with equality. Using this fact, we derive a necessary and sufficient condition for a set of vectors to be a complete system of MUBs or a SIC-POVM. This condition uses the orthonormality of a specific set of vectors. Then we define homogeneous systems, as a special case of systems of vectors for which the condition takes an especially elegant form. We show how known results and some new results naturally follow from this construction.
3

Geometrical Construction of MUBS and SIC-POVMS for Spin-1 Systems

Kalden, Tenzin 28 April 2016 (has links)
The objective of this thesis is to use the Majorana description of a spin-1 system to give a geometrical construction of a maximal set of Mutually Unbiased Bases (MUBs) and Symmetric Informationally Complete Positive Operator Valued Measures (SIC-POVMs) for this system. In the Majorana Approach, an arbitrary pure state of a spin-1 system is represented by a pair of points on the Reimann sphere, or a pair of unit vectors (known as Majorana vectors or M-vectors). Spin-1 states can be of three types: those whose vectors are parallel, those whose vectors are antiparallel and those whose vectors make an arbitrary angle. The types of bases possible for a spin-1 system are thus geometrically much more varied than for a spin-half system or qubit, which is the standard unit of information storage in most quantum protocols. Our derivation of the MUBs and SIC-POVMs proceeds from a recently derived expression for the squared overlap of two spin-1 states in terms of their M-vectors and the minimal additional set of assumptions that are needed. These assumptions include time-reversal invariance in the case of the MUBs and the requirement of three-fold symmetry in the case of the SIC-POVMs. The applications of these results to problems in quantum information are mentioned.

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