# 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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### proof that the gate U is equivalent to the given circuit mathematically

I have solved this question by this, but can't able to get my mistake in it.
550 views

### How to check if a quantum circuit can be constructed for a given matrix representation?

Let's say I have a matrix representation, e.g. $$\begin{pmatrix} 1 & 0 & 0 & 0 \\ 0 & 0 & 1 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 1 \end{pmatrix}.$$ How ...
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### Why can I not apply a control gate/function to a gate like T, S, S dagger, ... (using IBM Quantum Experience)? Is there another option?

I am trying to use the circuit composer of the IBM QE. I am doing the inverse QFT on 3 qubits and therefore need a control on T and S dagger gates, but it won't let me. Does anyone know why or know a ...
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### How to distinguish between collapsed and uncertain qubits in a quantum circuit?

I have been through the Young's double slit experiment. It's a direct proof or instance of showing that a wave is collapsed via observation or measurement, and shows no interference patterns. I want ...
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### An issue in plotting the quantum circuit using latex

Here's the code I'm working on: !pip install pylatexenc !pip install pillow qc = QuantumCircuit(2) qc.x(0) qc.cz(0,1) qc.x(0) qc.draw('latex') However there's an ...
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### how to plot probability histogram and/or bloch sphere of single qubit in multi-qubit quantum circuit in Qiskit?

How can I get statevector and/or blochsphere representation of qubits of my choice. For example I have 3 qubits with different gates being applied on each qubit. the qiskit state_vector simulator ...
66 views

### Weird Grover's Algorithm Behavior

I am attempting to use Grover's to find elements in an array that satisfy a comparative query (=, <, >, etc). I am using Qiskit, and am using a qRAM to encode my array. I have experimented with ...
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### Show that the two circuits are equivalent mathematically

This exercise wants me to prove the equivalence of the two circuits using their mathematical representations. Circuit 1: Circuit 2: Circuit 1 (q1 CNOT ...
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### How does this represent modular multiplication

How does this circuit map $|x\rangle$ to $|7x \space mod15\rangle$? Looking into Shor's and I thought that phase kickback causes the modular exponentiation part to be mapped onto the measurement ...
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### How can I fix this parametrization error in Qiskit?

I'm trying to use the parametrized circuits to run a single model of quantum circuit with different values. Here's part of my code: ...
206 views

### Computing the CDF with QAE in Qiskit

I want to load a lognormal distribution and then use an IntegerComparator to flip a qubit ($|0\rangle$ to $|1\rangle$) if its value is less than a threshold. Then I want to use an Quantum Amplitude ...
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### Unknown quantum circuit symbol

I was reading DiCarlo, L., Reed, M., Sun, L. et al. Preparation and measurement of three-qubit entanglement in a superconducting circuit. Nature 467, 574–578 (2010). https://doi.org/10.1038/...
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### Is Noise model for quantum prototypes accurate in Qiskit

We know that in Qiskit noise models modeling specific quantum machine prototypes exist and can be inserted into the code. However, are these models fixed in nature or they continuously improve ...
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### Device Repitition Rate on Melbourne

I've been receiving "Circuit runtime is greater than the device repetition rate " errors when running a relatively simple circuit on ibmq_16_Melbourne, but have had no issues ...
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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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### 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. https://ars.els-cdn.com/content/image/3-...