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:{%22cols%22:[[%22H%22],[%22H%22]]} However, if a CNOT control is added between the two ...
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1 vote
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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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1 vote
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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 ...
14 votes
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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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8 votes
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How to compute the measurement probability in swap test?

The figure of a circuit and the state are as follows. The final state before the measurement is $|O_{out}\rangle=\frac{1}{2}|0\rangle(|\phi\rangle|\psi\rangle+|\psi\rangle|\phi\rangle)+\frac{1}{2}|1\...
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Should C-NOT gate affect "input" qubit or not?

In MS presentation, they describe the process CNOT gate working with state machine diagram. At first they drew CNOT gate in ...
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12 votes
3 answers

Superposition of quantum circuits

Given a quantum circuit $C_1$ that generates a state $\vert\psi\rangle$ and another circuit $C_2$ that generates $\vert\phi\rangle$, is there a way to construct a circuit that outputs $$\frac{1}{\sqrt{...
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Quantum circuit, Fourier Transform/Decomposition?

Broadly speaking, can we say that quantum circuits are like Fourier Transform/Decomposition? We use qbit like waves, tune it with quantum gates, to find answer.
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What do we mean by “derive full operator of a quantum circuit” and to describe the mapping from input quantum registers to output quantum registers?

There is a quantum circuit with several Controlled NOT and Controlled swap gates, with two 2-qubit input registers X,Y and two 2-qubit output registers X',Y' where we have to find the mapping of the ...
3 votes
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Understanding the implementation of Grover's diffusion operator using the oracle qubit

I have two gates here for the Grover diffusion operator. The first gate is completely understandable for me, so I implemented it myself after submitting some papers that I read. This is the first ...
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5 votes
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Understanding quantum circuit diagrams: a circuit that compares two states $|YX\rangle$ and $|AB\rangle$

I have a quantum circuit which I would like to understand, which compares two standard basis states $|YX\rangle$ and $|AB\rangle$. It operates on the corresponding bits in each of the two states: i.e.,...
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