expectation value of an observable

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• Expectation value (quantum mechanics) — In quantum mechanics, the expectation value is the predicted mean value of the result of an experiment. It is a fundamental concept in all areas of quantum physics. Operational definition Quantum physics shows an inherent statistical behaviour:… …   Wikipedia

• Vacuum expectation value — Quantum field theory (Feynman diagram) …   Wikipedia

• Expectation-maximization algorithm — An expectation maximization (EM) algorithm is used in statistics for finding maximum likelihood estimates of parameters in probabilistic models, where the model depends on unobserved latent variables. EM alternates between performing an… …   Wikipedia

• Numerical sign problem — The numerical sign problem refers to the difficulty of numerically evaluating the integral of a highly oscillatory function of a large number of variables. Numerical methods fail because of the near cancellation of the positive and negative… …   Wikipedia

• Perturbation theory (quantum mechanics) — In quantum mechanics, perturbation theory is a set of approximation schemes directly related to mathematical perturbation for describing a complicated quantum system in terms of a simpler one. The idea is to start with a simple system for which a …   Wikipedia

• Density functional theory — Electronic structure methods Tight binding Nearly free electron model Hartree–Fock method Modern valence bond Generalized valence bond Møller–Plesset perturbation theory …   Wikipedia

• Liouville's theorem (Hamiltonian) — In physics, Liouville s theorem, named after the French mathematician Joseph Liouville, is a key theorem in classical statistical and Hamiltonian mechanics. It asserts that the phase space distribution function is constant along the trajectories… …   Wikipedia

• Jaynes-Cummings model — The Jaynes Cummings model (JCM) is a theoretical model in quantum optics. It describes the system of a two level atom interacting with a quantized mode of an optical cavity, with or without the presence of light. The JCM is of great interest in… …   Wikipedia

• Wave function — Not to be confused with the related concept of the Wave equation Some trajectories of a harmonic oscillator (a ball attached to a spring) in classical mechanics (A B) and quantum mechanics (C H). In quantum mechanics (C H), the ball has a wave… …   Wikipedia

• Uncertainty principle — In quantum physics, the Heisenberg uncertainty principle states that locating a particle in a small region of space makes the momentum of the particle uncertain; and conversely, that measuring the momentum of a particle precisely makes the… …   Wikipedia

• Quantum state — In quantum physics, a quantum state is a mathematical object that fully describes a quantum system. One typically imagines some experimental apparatus and procedure which prepares this quantum state; the mathematical object then reflects the… …   Wikipedia