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An “effective spin” concept is introduced to underpin the fundamental analogy between two disparate fields of physics – phase coherent transport in mesoscopic systems and spin-based quantum information processing. When coupled with the Bloch sphere concept, this isomorphism allows formulation of transport problems in a language more familiar to researchers in the field of spintronics and quantum computing. We exemplify the synergy between charge tunneling and spin qubit unitary operations by recasting well-known problems of tunneling through a delta scatterer, a resonant tunneling structure, a superlattice structure, and arrays of elastic scatterers, in terms of specific unitary operations (rotations) of a spinor on the Bloch sphere. Furthermore, we examine the potential use of random arrays of elastic scatterers as quantum information processors by calculating the properties of their Shannon entropy under the assumption of phase coherent charge transport. The numerical values of the Shannon entropy average and variance are very sensitive to the nature of the impurities, whether attractive, repulsive, or a combination of both; besides, the inclusion of evanescent modes has a profound influence on the value of the Shannon entropy and its associated signal-to-noise ratio (SNR). In samples with repulsive scatterers, the SNR can be tuned over a wide range by applying a potential through a gate to change the impurity potentials from repulsive to attractive by moving their energy levels with respect to the quasi-Fermi level in the sample.

One of the most promising paradigms for the development of novel high-speed and energy efficient devices is spin electronics or spintronics. It is based on the simultaneous manipulation of the electron spin and large degrees of freedom. It offers the possibility of developing electronic devices based on the control of the electron spin. The spin polarization of a single electron can exist in a coherent superposition of two orthogonal spin polarizations (i.e. mutually anti-parallel spin orientations) for a relatively long time without losing the phase coherence. The charge degree of freedom, on the other hand, loses phase coherence much faster. Therefore spin has become the preferred vehicle to host a quantum bit (or "qubit") which is a coherent superposition of two orthogonal states representing classical logic states of 0 and 1. The potential application of spin manipulation to a scalable quantum logic processor has led to the field of quantum computing.To date, several physical quantum computers have been proposed which all require appropriate mechanisms to create, manipulate and measure individual spins. Each operation can be mapped to the action of a quantum-mechanical system acting on the spin state of the electron also known as the qubit state. The Bloch sphere is a useful tool to represent the actions of various quantum-mechanical operators on a spinor because it provides a visual representation of the qubit state evolution. Most importantly, it provides a link between the rather abstract concept of a spinor and the more intuitive way (although not rigorous) of thinking of the spinor of the electrons being associated with an intrinsic magnetic moment.In this thesis, a simulation software is built to provide a visual representation of a quantum state or qubit based on the Bloch sphere representation. This software uses the Java language and libraries to provide a multi-platform simulator that can be quickly distributed and viewed using the Java web-start technology. This simulator shows the different qubit states, their representation in both the two dimensional complex plan along with the bra-ket representation. It provides the ability to visualize simple basic operators representing the action of quantum gates. It allows the user to enter simple operations which can be represented by the action of 2x2 matrices. It also features some more complex functionality important in spintronics including the Larmor precession and the spin flip process under the combined action of a constant and rotating magnetic field as described by the Rabi formula.

Electron spin, alone or in conjunction with charge, can be used to process information and build up quantum computers because it is a natural quantum bit. In this work, a Java simulator has been constructed and a 3D display has been created using Java 3D API to animate the motion of a qubit or spinor based on the Bloch sphere and Bloch ball concepts. The simulator is capable of illustrating the Larmor precession of a qubit, the Rabi formula which calculates the probability of spin flip in a time dependent magnetic field, and the density matrix concept where the time evolution of an ensemble of spinors can be examined. Control panels are constructed on the user interface to allow manipulation of qubits and adjustment of simulation parameters such as external time-independent and time-dependent magnetic fields. The simulator provides a user friendly software package useful for teaching and self-learning in the field of spintronics.