Fundemental of Quantum Computing Quantum Logic - Qubit A qubit (or quantum bit) is the quantum mechanical analogue of a classical bit. Unlike the traditional computing system which the bit only represented one state (either 1 or 0), qubit can represented both state simultaneously because of the concept in quantum mechanics called superposition.
Superposition
Concept : a fundamental principle in quantum mechanics that allows qubits to exist in multiple states simultaneously. Representation: the state of quantum particle can be visualized form a form called Bloch Sophere and Bloch Circle as an arrow pointing in 3D space. If the arrow points up, it represents the 0 state; if it points down, it represents the 1 state. However, in superposition, the arrow can point in any direction, signifying a combination state of 0 and 1 like the following formula($\alpha, \beta$ is the probability for the state): $$ \Psi = \alpha\vert0\rangle + \beta\vert1\rangle$$ Measurement: when we want to measure a qubit, it collapses into one of the basis states (0 or 1) with a probability determined by the direction of the arrow. The more upward the arrow points, the higher the probability of measuring 0. So the measured direction would determined the result of the qubit’s state. Entanglement
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