Qubits and Superposition: The Quantum Building Block of Computation

Abstract: Quantum computing exploits quantum mechanical principles to perform computations unachievable by classical systems. Coherent superpositions of states enable quantum parallelism and interference supported by the qubit, the basic unit of quantum computing. This work examines the role of qubits and superposition in quantum information that processes through theoretical foundations and visual simulations. Core formalisms for single-qubit systems are presented, including Dirac notation, unitary and Hermitian            , and state evolution. With particular attention to the Hadamard gate for generating and reversing superpositions. The Bloch sphere provides a geometric framework to illustrate the action of single-qubit gates. Qiskit simulations in Python are used to visualise the influence of global and relative phases on qubit dynamics. Physical qubit implementations such as superconducting circuits, trapped ions, and photonic systems are briefly surveyed for context. A practical contribution is the application of the Variational Quantum Eigensolver (VQE) to simulate the dissociation curve of the hydrogen molecule (H₂) and demonstrate the usefulness of hybrid quantum-classical methods for molecular energy calculations in near-term devices. This study highlights the central importance of accurate phase manipulation and single-qubit control in advancing quantum computing by linking mathematical structure, simulation, and application.