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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The statevector of the quantum circuit

I have tried to solve this problem many times. But I can't solve this. Please somebody help me. (prep has no meaning) ${O_1}$ : $O_2$: What is the state vector $|\psi\rangle$ (for qubits 1 and 2) ...
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What is the quantum leap / advantage of quantum computers? [duplicate]

I have read up several times on various sources about the advantage of quantum computers but still, I can only reproduce statements without really understanding them. Why are quantum computers able to ...
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How does a quantum circuit capture the "non-halting ability" of classical Turing machines?

It is claimed that a quantum Turing machine is "computationally" equivalent to the circuit model. Quantum computing also includes all classical computing. However, we know that there are ...
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What is the difference between the two entanglement circuits?

For a three qubits system to be in an entanglement(GHZ) state, the circuit can be built as per Qiskit, Here, the control bit of the second X gate is on q0. what if the control bit is shifted to q1. ...
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From the final quantum state to the quantum circuit composition

When I build a quantum circuit and my initial state is the one composed only by zeros ($|000\ldots 0\rangle$), I have a final state $|\psi\rangle$ that is the result of the application of the quantum ...
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Symmetric Universal Quantum Cloning Machine (UQCM) N --> M for unknown states

Does it exist a schematic diagram of the quantum circuit implementing the symmetric UQCM N--> M for unknown states? If yes, does anyone know a Qiskit implementation of it?
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Compute the output of this Approximate Quantum Cloning three-qubit circuit

Above is a circuit for "Approximate Quantum Cloning" The preparation state is given by $$|\psi\rangle =\alpha|0\rangle+\beta|1\rangle$$ The gates labelled $\theta_i$ denote single qubit ...
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How should I think about circuit metrics like "qubit count," "circuit depth," and "gate count" when dealing with the OpenQASM 3 ctrl modifier?

It seems like circuit metrics like qubit count, circuit depth, and gate count are pretty useful. Qubit count determines whether a it's even possible to run a program on resource-limited quantum ...
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Tweak the parameter p of QAOA in qiskit

I am solving a QUBO using QAOA. It works flawlessly with default parameters for smaller instances of the problem, but my RAM is saturated when I try to solve a problem of size 15. I suspect this can ...
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How to tranfer given superposition to quantum circuit?

Let's say I have a superposition of qubit defined as $\frac{1}{2} (| 000 \rangle + | 001 \rangle + | 111 \rangle + | 110 \rangle)$ (as given in the answer here: Explanation of output produced by the ...
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Evaluating the derivative of a Quantum Circuit

After this post this weekend which got an excellent response, I've been trying to get into the solution that is given by the paper and applying it to my circuit. My original circuit is far bigger and ...
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What exactly is the "quantum singular value decomposition"?

I know what is singular value decomposition, meaning given a matrix and write it as multiplication three different matrices, and middle matrix being diagonal and entries are singular values. So, what ...
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Apply readout error mitigation to mid-circuit measurement

I'm trying to construct a quantum circuit with 3 mid-circuit measurements, here's an example: ...
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Is there a quantum circuit builder package that allows you to import/export a circuit as a JSON?

I've done a superficial search in each of the qiskit, cirq, and braket open source repositories for such a feature, but can't find any explicit examples of this functionality. I'm wondering if anyone ...
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FRQI wrong interpretation

I try to use FRQI https://qiskit.org/textbook/ch-applications/image-processing-frqi-neqr.html with the same circuit. Suppose I have the following image: and the flatten representation is [0 100 200 ...
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Minimum number of 2 qubit gates to build any unitary

Any unitary $U$ acting on $N$ qubits can be decomposed in a finite product $U=U_1U_2...U_n$ where every $U_i$ acts on only 2 qubits, for example through decomposition in CNOT, phase shifts and 1 qubit ...
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FRQI for 8x8 image

I read the paper A flexible representation of quantum images for polynomial preparation, image compression, and processing operations and found a scheme for 2x2 images which looks like this: I tried ...
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Understanding Constant Multiplication Circuit for Binary Field - How to Construct Quantum Circuit from Linear Mapping

I was thinking to ask this on Math Stackexchange, but maybe here would be better since I also hope the answers also explain from quantum computation context. Problem So I was reading the paper "...
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Measuring in qiskit collapses onto the Z-Plane. Why do any rotations other than Y matter?

We have the situation where a 50/50 split between $|1\rangle$ and $|0\rangle$. This was done using a $H$-Gate. Now, when measuring in qiskit, if my understanding is ...
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What is the shortest-circuit-depth quantum-benchmarking algorithm?

An algorithm implementing a model whose results are known, and from the known results, the benchmarking of the device could be done. What is the currently known shortest circuit depth algorithm that ...
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Four-qubit error correction code

$\newcommand{\ket}{\left|#1\right>}$ Consider the following 4-qubit code which allows you to detect a bitflip and/or a phaseflip. The logical 0 and 1 are encoded as: \begin{align*} \ket{0}_{...
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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 ...
Let's assume that I have a density matrix $\rho$ that consists of $N$ qubits. If this density matrix undergoes an error-channel that swaps any two qubits with an equal probability, i.e.  \mathcal{E}(...
Why do we care about the number of $T$ gates in a quantum circuit?
When reading this question and quickly reading some of the linked papers, I wondered why was the number of $T$ gates specified along the number of controlled-$X$ gates. I've often read that ...