# Questions tagged [quantum-circuit]

a model in which a computation is a sequence of quantum gates, which are reversible transformations on an n-qubit register (the quantum-mechanical analog of an n-bit register)

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### A CNOT between two Hadamard gates: why does the CNOT changed the output of the second Hadamard gate?

Applying the Hadamard gate twice in a row, it restores the original input: https://algassert.com/quirk#circuit={%22cols%22:[[%22H%22],[%22H%22]]} However, if a CNOT control is added between the two ...
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### Question about a circuit from "Quantum Computing for Computer Scientists"

I am trying to implement a basic quantum computing emulator. In the chapter on Grover's algorithm, we're shown the following circuit: They demonstrate Grover's algorithm with a function $f$ that ...
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### How to understand the circuits used for magic state distillation in surface code?

I'm reading about surface code theory recently (Phys. Rev. A 86, 032324). When I come across the magic state distillation part, it is difficult for me to understand the circuits. In addition, I have ...
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### Transforming $|100\rangle$ state into $|000\rangle + |111\rangle$ state using only Hadamard and CNOT gates

Hi, How to convert $|100\rangle$ 3-qubit quantum state into $\frac{1}{\sqrt{2}}(|000\rangle + |111\rangle)$ state using only Hadamard and CNOT gates? Also, is output state an entangled one?
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### How to change the names of the registers displayed with circuit_drawer (output='mpl')

I am trying to change the appearance of the circuit_drawer in output='mpl' mode. The registers of the Quantum Circuit are named like ($q0_0$, $q0_1$, $q1_0$, $q2_0$, $q2_1$,..) but I'd like to name ...
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### What's meant by the depth of a quantum circuit?

I'm using Qiskit to create quantum circuits wherein I've this attribute called depth. The documentation states it is the length of the critical path here. What does ...
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