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I read "...an $n$ qubit array can represent $2^n$ possible array elements.." on this post. A classical $n$-bit array can represent $2^n$ possible array elements as well, so I'm confused about the difference. Does it mean that the $2^n$ possibilities represented by the $n$-qubit array are represented at the same time?

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Now here is where it gets deep an 𝑛 Qubit Array can represent $2^𝑛$ possible array elements (consult anywhere online for an explanation of that or drop a comment).

And similarly an 𝑛 Qubit quantum operator can act on that entire $2^𝑛$ quantum space, and produce an answer that we can interpret.

It's probably not too clear here, but I think the OP meant, an $n$ qubit array can represent any state that is a linear combination of $2^n$ basis states.

So, a classical array of 1 bit could represent any state 0 or 1 ($2^1$ possibilities), but a single qubit could be in any state $\alpha |0\rangle + \beta |1\rangle $ where $|\alpha|^2 + |\beta|^2 = 1$, so an infinite number of possibilities made from a basis of $2^n$ states.

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