"Let’s begin by labeling the possible spin states along the three coordinate axes. If A is oriented along the z axis, the two possible states that can be prepared correspond to σ(adsbygoogle = window.adsbygoogle || []).push({}); _{z}= ±1. Let’s call them up and down and denote them by ket-vectors |u> and |d> . Thus, when the apparatus is oriented along the z axis and registers +1, the state |u> has been prepared. " says in The Theoritical Minimum

what it means ? In particular "the state |u> has been prepared" Actually I am asking just this part

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# Quantum State Vector

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