Theses and Reports

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To obtain a copy of the thesis, [please write to me].

  • Vibrating Sample Magnetometery: Analysis and Construction

Syed Alamdar Hussain Shah, SBASSE Physics Major, LUMS (2014). Co-supervisor with Dr. Anzar Khaliq (LUMS). This is a report for senior project.

This project primarily aims at developing a vibrating sample magnetometer (VSM) for measuring the magnetization of any material sample. The project deals with basic physics and methodology of magnetometery. Different magnetometer schemes are reviewed and a special focus is paid to VSM. A detailed analysis on the mechanism required for vibrating a physical sample is being done. Different detection schemes with different geometries of Faraday coils are tested and aimed at the lab implementation and some experimental results.

Click here for the thesis.

  • A Gentle Introduction to Quantum Computing

Abdullah Khalid, SSE Physics Major, LUMS. This is a report for an independent study project

Click here for the study report.

  • Differential detection of Faraday Rotation, Generation and Detection of Elliptically Polarized Light

Hafiz Muhammad Ahmad Masood, B.Sc. University of the Punjab (2010). Co-supervisor with Prof. Munazza Zulfiqar, Punjab University.

Click here for the thesis summary.

  • Phase-sensitive Faraday rotation on terbium gallium garnet crystal and various diamagnetic liquids

Aysha Aftab, M.Phil Physics, University of the Punjab (2009). Co-supervisor with Prof. Dr. Saadat Anwar Siddiqi, Punjab University.

Click here for the thesis summary.

  • Concomitant Gradients in Magnetic Resonance Imaging

Rafiullah, B.Sc. Honours Physics, University of the Punjab (2008). Co-supervisor with Prof. Dr. Mahmood-ul-Hassan, Punjab University.

Magnetic Resonance Imaging (MRI) is a beautiful application of the phenomenon of Nuclear Magnetic Resonance (NMR). MRI's foremost identity lies in being a non-invasive diagnostic technique, but in fact, it has many other very important applications in biology, engineering and materials science. Classically, the field strength is regarded as one major measure of its quality because high field strength gives higher signal to noise ratios, better resolution and reduced scan times. So high field MRI has historically drawn a lot of attention.

However high field MRI has some disadvantages like reduced relaxation times and high susceptibility gradients. Furthermore high field MRI systems are bulky, immovable and very expensive. These reasons have motivated interest in the subject of low field MRI. The downside is that in the low field regime, we encounter the problem of undesired inhomogeneous fields (gradients) appearing along with the desired ones. The presence of these additional gradients, generally known as concomitant gradients, directly follows from the fundamental Maxwell equations. The concomitant gradients cause strong image distortions. This is one of the most crucial handicaps of low field MRI.

In this manuscript we discuss concomitant gradients and work out their quantitative contribution towards the resulting image distortion. An introduction to the basics of NMR is outlined in the first chapter. Extending the basics of NMR, a brief account of MRI is presented in chapter 2. We have introduced and demonstrated a new method of MRI simulations with significantly reduced processing times in chapter 3. In chapter 4, we address concomitant gradients. We have computed the contribution of concomitant gradients analytically and simulated results for various arrangements of the gradient fields.

  • Numerical Optimization of Pulse Sequences for NMR Quantum Information Processors

Saman Naseer, B.Sc. Honours Physics, University of the Punjab (2008). Co-supervisor with Prof. Dr. Mahmood-ul-Hassan, Punjab University.

The technique of nuclear magnetic resonance (NMR) makes use of various radio frequency pulses for the transference of the nuclear magnetization vector form one state to the other. In addition, one form of quantum information processing (QIP) utilizes NMR to implement unitary (and non-unitary) dynamics with the far-reaching goal of realizing computers that can surpass their classical counterparts. NMR based QIP, that is the focus of this dissertation, involves designing accurate unitary transformations of the spin state. The overlap of the theoretical and experimentally achieved values, called the fidelity, is an important parameter in the design of robust, accurate unitary transformations. Besides, the transformations need also be time optimal.

In this one year undergraduate research project we used gradient-based optimization methods for designing pulse sequences for NMR based QIP. These sequences implement unitary operations. The goal of the optimization was to achieve high fidelities. Specially, we used gradient ascent pulse engineering (GRAPE) as the optimization paradigm.

An introduction to the basics of NMR is given in Chapter 1. Chapter 2 covers basic gradient-based optimization techniques and line search methods, especially the methods that are relevant to the present work. The next two chapters cover the formulation and implementation of the GRAPE algorithm. We have used the GRAPE algorithm along with line search to engineer pulse sequences for state-to-state transfer as well as the more general problem of unitary transformation design. We study the role of algorithmic parameters in quantum fidelity maximization, the number of steps required to achieve maximal fidelity and the robustness of the algorithm with respect to the choice of initial controls. We determine that the algorithm also returns results that are known to be optimal from the analytical perspective. This work helps us in understanding better the modus operandi of the GRAPE algorithm itself. Last, the present work also includes the design of pulse sequences that are robust against pulse width errors.

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