Quantum reference frame: Difference between revisions

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==Quantum reference frame==

A reference frame can be treated in the formalism of quantum theory, and, in this case, such is referred as a quantum reference frame. Despite different name and treatment, a quantum reference frame still shareshares much of the notions with a reference frame in [[classical mechanics]]. It is still defined with the same definition. It is still always associated to some physical system., Andand it is still[[Relational alwaysquantum mechanics|relational]].

For example, if a [[spin-1/2]] particle is said to be in the state <math>|\uparrow z \rangle</math>, a reference frame is implicitly implied, and it can be understood to be some reference frame with respect to an apparatus in a lab. It is obvious that the description of the particle does not place it in an absolute space, and doing so would make no sense at all because, as mentioned above, absolute space is empirically unobservable. On the other hand, if a magnetic field along y-axis is said to be given, the behaviour of the particle in such field can then be described. In this sense, ''y'' and ''z'' are just relative directions. They do not and need not have absolute meaning.