Quantum Fundamentals
A Brief History of Quantum Mechanics
Quantum mechanics emerged in the early 20th century as scientists like Max Planck, Albert Einstein, Niels Bohr, and Erwin Schrödinger explored the strange behavior of matter and energy at atomic and subatomic scales. Unlike classical physics, quantum mechanics describes phenomena where particles can exist in multiple states at once and outcomes are fundamentally probabilistic. This new framework revolutionized our understanding of the universe and laid the foundation for modern quantum technologies.
What is a Quantum System?
A quantum system is any physical system that exhibits quantum behavior—such as superposition, entanglement, and quantization of energy. Examples include electrons in an atom, photons of light, or even engineered systems like superconducting circuits. Quantum systems are described mathematically by wavefunctions, which encode the probabilities of finding the system in various possible states.
What is a Qubit?
A qubit (quantum bit) is the basic unit of quantum information, analogous to a classical bit but with unique properties. Unlike a classical bit, which can be either 0 or 1, a qubit can exist in a superposition of both states simultaneously. This allows quantum computers to process information in ways that are impossible for classical computers, enabling powerful new algorithms and applications.
The Bloch Sphere and Probabilistic Nature of Qubits
The state of a single qubit can be visualized on a Bloch sphere—a 3D representation where any point on the sphere corresponds to a possible qubit state. The north and south poles represent the classical states |0⟩ and |1⟩, while all other points represent superpositions. When a qubit is measured, its state "collapses" probabilistically to either |0⟩ or |1⟩, with probabilities determined by its position on the Bloch sphere. This inherent randomness is a fundamental feature of quantum mechanics and underpins the power and complexity of quantum computing.