I'm trying to perform QPE on the T-gate in Quirk but I'm not getting the correct result. For the T-gate, I should be measuring (001) with 100% probability, but instead, I'm getting the following:

I've modeled my implementation directly from the Qiskit QPE tutorial. For the unitary I am using $U(\lambda) = \begin{bmatrix}1 & 0\\0 & e^{i \lambda}\end{bmatrix}$.

Where did I go wrong here? Thank you in advance.

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    $\begingroup$ The angle should get smaller. not bigger, for the controlled gates on further-apart qubits. $\endgroup$ – Craig Gidney Dec 14 '20 at 5:51

Your implementation is really close - on the website, here's the diagram that they used: circuit

So, I think you reversed the angles - it should be $-\pi/2, -\pi/4, -\pi/2$. (Also: there's a QFT inverse that Quirk has, so you can verify that the first half of your circuit is correct).


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