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Home > Wavefunction collapse

In general, quantum systems exist in a superposition of basis states, and evolve according to the time dependent Schrödinger equation, which is one of the two processes. The contribution of each basis state to the overall wavefunction is called the amplitude. However, when the wavefunction collapses, which is the other process, from an observer's perspective the state seems to "jump" to one of the basis states and uniquely acquire the value of the property being measured that is associated with that particular basis state.

Upon performing measurement of an observable A, the probability of collapsing to a particular eigenstate of A is directly proportional to the square modulus of the (generally complex) amplitude associated with it. Hence, in experiments such as the double-slit experiment each individual photon arrives at a discrete point on the screen, but as more and more photons are accumulated, they form an interference pattern overall. After the collapse, the system begins to evolve again according to the Schrödinger equation.

The cluster of phenomena described by the expression wavefunction collapse is a fundamental problem in the interpretation of quantum mechanics known as the measurement problem. The problem is not really confronted by the Copenhagen interpretationThe Copenhagen interpretation is the mainstream interpretation of quantum mechanics; it was mostly worked out by Niels Bohr and Werner Heisenberg while collaborating in Copenhagen around 1927. Bohr and Heisenberg extended the probabilistic interpretation which simply postulates that this is a special characteristic of the "measurement" process. The Everett many-worlds interpretation deals with it by discarding the collapse-process, thus reformulating the relation between measurement apparatus and system in such a way that the linear laws of quantum mechanics are universally valid, that is, the only process according to which a quantum system evolves is governed by the Schrödinger equation. Often tied in with the many-worlds interpretation but not limited to it is the physical process of decoherence, which causes an apparent collapse.

Note that a general description of the evolution of quantum mechanical systems is possible by using density operators and quantum operationIn quantum mechanics, a quantum operation is a mathematical formalism used to describe a broad class of transformations that a quantum mechanical system can undergo. This formalism describes not only time evolution or symmetry transformations of isolateds. In this formalism (which is closely related to the C*-algebraic formalism) the collapse of the wave function corresponds to a non-unitary quantum operation.

Shahriar Afshar's experiment

In March 2004, Shahriar Afshar announced at Harvard UniversityHarvard University is a private university in Cambridge, Massachusetts, USA and a member of the Ivy League. It was founded on September 8, 1636 by a vote of the Great and General Court of the Massachusetts Bay Colony, making it the oldest post-secondary s the results of a variation on the two-pin-hole "which-way" experiment (similar to the double-slit experiment) in which he claims to have disproved Bohr'sNiels Henrik David Bohr ( October 7, 1885 November 18, 1962) was a Danish physicist who made essential contributions to understanding atomic structure and quantum mechanics. Bohr's contributions to physics Bohr's model of atomic structure. The theory that Principle of Complementarity, also reported in the July 24 edition of New Scientist. [1] [2] [3]

Using his experiment it is possible to detect interference fringes even when observing the path of a photon stream, indicating that the wavefunction does not collapse. If his results are verified, it has far-reaching implications for the understanding of the quantum world, and invalidates the Copenhagen interpretation. It would also seem to invalidate the Many-worlds interpretation which predicts that there should be no interference between wave functions in universes that are physically distinguishable.

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Topics: Wavefunction Collapse Quantum Interpretation Experiment Process...

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Wavefunction collapseIn quantum mechanics, wavefunction collapse is one of two processes by which quantum systems apparently evolve. It is also called collapse of the state vector''. As of March 2004, wavefunction collapse appears to have been disproven. In general, quantum s WavefunctionA wavefunction is a mathematical description of the density in space of the wave associated with a particle, such as an electron in an atom, or with a group of particles, such as all of the easily movable electrons in a copper wire. In quantum mechanics t