Interaction of a quantum system with a classical observer
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Quantum mechanics
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In quantum physics, a measurement is the testing or manipulation of a physical system to yield a numerical result. A fundamental feature of quantum theory is that the predictions it makes are probabilistic. The procedure for finding a probability involves combining a quantum state, which mathematically describes a quantum system, with a mathematical representation of the measurement to be performed on that system. The formula for this calculation is known as the Born rule. For example, a quantum particle like an electron can be described by a quantum state that associates to each point in space a complex number called a probability amplitude. Applying the Born rule to these amplitudes gives the probabilities that the electron will be found in one region or another when an experiment is performed to locate it. This is the best the theory can do; it cannot say for certain where the electron will be found. The same quantum state can also be used to make a prediction of how the electron will be moving, if an experiment is performed to measure its momentum instead of its position. The uncertainty principle implies that, whatever the quantum state, the range of predictions for the electron's position and the range of predictions for its momentum cannot both be narrow. Some quantum states imply a near-certain prediction of the result of a position measurement, but the result of a momentum measurement will be highly unpredictable, and vice versa. Furthermore, the fact that nature violates the statistical conditions known as Bell inequalities indicates that the unpredictability of quantum measurement results cannot be explained away as due to ignorance about "local hidden variables" within quantum systems.
Measuring a quantum system generally changes the quantum state that describes that system. This is a central feature of quantum mechanics, one that is both mathematically intricate and conceptually subtle. The mathematical tools for making predictions about what measurement outcomes may occur, and how quantum states can change, were developed during the 20th century and make use of linear algebra and functional analysis. Quantum physics has proven to be an empirical success and to have wide-ranging applicability. However, on a more philosophical level, debates continue about the meaning of the measurement concept.
and 23 Related for: Measurement in quantum mechanics information
Inquantum physics, a measurement is the testing or manipulation of a physical system to yield a numerical result. A fundamental feature of quantum theory...
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Quantummechanics is the study of matter and its interactions with energy on the scale of atomic and subatomic particles. By contrast, classical physics...
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reduction to explain quantummeasurement. [citation needed] Inquantummechanics each measurable physical quantity of a quantum system is called an observable...
all quantum physics, which includes quantum chemistry, quantum field theory, quantum technology, and quantum information science. Quantummechanics can...
mathematical formulations of quantummechanics are those mathematical formalisms that permit a rigorous description of quantummechanics. This mathematical formalism...
moreover quantummechanics provides a recipe for calculating this probability distribution. Indeterminacy inmeasurement was not an innovation of quantum mechanics...
taken longer—in one case, 10,000 times longer—than the interval between the measurements. According to some interpretations of quantummechanics, the effect...
Copenhagen interpretation is a collection of views about the meaning of quantummechanics, stemming from the work of Niels Bohr, Werner Heisenberg, Max Born...
is a postulate of quantummechanics that gives the probability that a measurement of a quantum system will yield a given result. In its simplest form...
explained by classical mechanics. Beginning out of attempts to extend the understanding of quantummechanics, the theory has developed in several directions...
measurement. This also implies that there is not a clear or neat distinction between estimation and measurement. Inquantummechanics, a measurement is...
In physics and the philosophy of physics, quantum Bayesianism is a collection of related approaches to the interpretation of quantummechanics, the most...
self-Hamiltonian of the system. In a sense, QND measurements are the "most classical" and least disturbing type of measurementinquantummechanics. Most devices capable...
of experimental tests in classical mechanics forms a Boolean algebra, but the structure of experimental tests inquantummechanics forms a much more complicated...
information and measurement is required in order to quantify the observation, making this crucial to the scientific method. Inquantummechanics, due to the...
Matrix mechanics is a formulation of quantummechanics created by Werner Heisenberg, Max Born, and Pascual Jordan in 1925. It was the first conceptually...
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