Wave function collapse: Difference between revisions

Revision as of 23:17, 7 October 2004

Revision as of 00:39, 8 November 2004

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In [[quantum mechanics]], the '''collapse of the [[wavefunction]] collapse''' is a name given historically to one of two processes by which [[quantum system]]s 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 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.

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Note that a general description of the evolution of quantum mechanical systems is possible by using [[density matrix|density operators]] and [[quantum operation]]s. 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 University]] the results of a variation on the similar [[two-pin-hole "which-way" experiment]] in which he claims to have disproved [[Niels Bohr|Bohr's]] [[Principle of Complementarity]], also reported in the [[July 24]] edition of ''[[New Scientist]]''.

[http://www.sciencefriday.com/images/shows/2004/073004/AfsharExperimentSmall.jpg]

[http://my.harvard.edu/cgi-bin/webevent/webevent.cgi?cmd=showevent&ncmd=calmonth&cal=9719&y=2004&m=3&d=23&id=10416384&token=G6409379:1&sb=0&cf=cal&lc=calmonth&swe=1&set=0&sa=0&sort=e,m,t&ws=0&sib=0&de=0&tf=0]

Using his experiment it is possible to detect interference fringes even when observing the path of a photon stream, indicating that the [[wave function]] 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]].

[[Category:Quantum mechanics]]