24 votes
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What is postselection in quantum computing?

"Postselection" refers to the process of conditioning on the outcome of a measurement on some other qubit. (This is something that you can think of for classical probability distributions and ...
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10 votes

What is postselection in quantum computing?

As the other answer conveyed (and to which I am just trying to provide some clarification), post-selection is about just looking at a subset of possible measurement outcomes. To my mind, this falls ...
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4 votes
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HHL algorithm -- problem with the outcome of postselection

Your intuition is correct for a single qubit, in that if I measure $$\alpha\vert 0 \rangle + \beta\vert 1 \rangle$$ I would get either $\vert 0 \rangle$ or $\vert 1 \rangle$. But since the qubits are ...
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3 votes

HHL algorithm -- problem with the outcome of postselection

You are half right, in that the $C$ factor is only kept there for (what I assume being) explanatory purposes. However, the $1/\lambda_j$ factors definitely stays there after postselection. One way to ...
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1 vote

How to select the statevetor of a qubit in a multiqubit circuit in qiskit?

You can use save_statevector with conditional = True, like that: ...
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1 vote

Post-selection applied to quantum teleportation

As I understand it, the key caveat to postselection, at least in regards to retrocausal effects, is that Bob already knows what state Alice will post-select. Since he already knows what she will do, ...
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1 vote

On the probability of preparing of a uniform superposition by performing a controlled-multiplication and post-selecting $0$

CW from self-answer, and also because this is more of an extended comment than an answer. Let $A$ be the adjacency matrix of the Cayley graph of our group $\mathcal{H}$ of order $N$. Notice that $A$ ...
1 vote
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How is postselection used in quantum tomography?

In principle, Bob here just has to guess the $2\times 2$ matrix $\sigma$. If he starts with any parametric state $\sigma(\alpha,\beta)$ with $\alpha,\beta\in\mathbb{C}$ and measures the outcome Tr$(M\...
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