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Equation 90 · Part 1 · The Atlas That Refuses to Close

Symbol A_w

Aw=⟨f∣A^∣ψ⟩⟨f∣ψ⟩,A_w = \frac{\langle f|\hat A|\psi\rangle}{\langle f|\psi\rangle},
AwA_w

What this part means

conditioned on that postselection.

Its job in the formula

AwA_w is part of the quantity the equation computes from the expression on the right.

Where the article explains it

The weak value of any observable A^\hat A , position among them, conditioned on that postselection is

The passage around this formula

…formula]. introduced by Aharonov, Albert, and Vaidman as the quantity a weakly coupled pointer’s mean shift actually reports, to leading order in the coupling strength, once the postselection has been performed [ 11 ] . AwA_w is not an eigenvalue of A^\hat A , not an expectation value in the ordinary sense, and not guaranteed to be real: it is built from an amplitude ratio over a sub-ensemble selected by an event, the postselection, that has not yet happened at the time the weak coupling acts.

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Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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Sources cited in the surrounding passage

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