## Definition Quantum superposition is a foundational principle of [[quantum mechanics]] that describes the ability of a quantum system to exist in multiple states simultaneously. ## Key Characteristics - **State Combination**: A quantum system can be in a combination (or superposition) of all its theoretically possible states. The state of a quantum system is described by a wave function. - **Probability Amplitude**: Each state in superposition has a probability amplitude associated with it. The squared magnitude of the amplitude gives the probability of finding the system in that state upon measurement. - **Collapse Upon Measurement**: When a measurement is made on a quantum system, its superposition collapses into a single state, corresponding to the measurement result. ## Schrödinger's Cat Thought Experiment - This thought experiment, proposed by physicist Erwin Schrödinger, illustrates the counterintuitive nature of quantum superposition. A cat is placed in a sealed box with a radioactive atom that, if it decays, releases poison and kills the cat. Until observed, the cat is simultaneously both alive and dead due to the atom's superpositioned decay and non-decay states. ## Applications - **[[Quantum Computing]]**: Quantum bits (qubits) leverage superposition to represent both 0 and 1 simultaneously, enabling powerful computational capabilities. - **Quantum Interference**: Superposition enables quantum interference, which is utilized in many quantum algorithms and protocols. - **[[Quantum Cryptography]] & Communication**: Superposition properties are key to many quantum cryptographic protocols. ## Philosophical and Scientific Implications - **Nature of Reality**: Quantum superposition challenges classical intuitions about the definite state of physical systems, leading to numerous interpretations of [[quantum mechanics]]. - **Observer's Role**: The act of measurement and its role in collapsing superposition has sparked debates on the observer's role in determining reality. ## Related Concepts - **[[Quantum Mechanics]]**: The overarching theory describing phenomena like superposition. - **[[Quantum Entanglement]]**: Another non-classical property of quantum systems, where particles become interconnected in their states. - **Wave Function**: A mathematical function that provides a probability distribution of a quantum system's states.