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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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What is a gate-level circuit used in the 2022 Jafferis et al. experiment on Sycamore?

A recently published Nature paper of Jafferis et al. describes an experiment with a handful of qubits performed on Google's Sycamore processor to explore the SYK model in the context of AdS/CFT and ...
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Is circuit cutting equivalent in anyway to quantum teleportation?

I've been introduced recently to circuit cutting, and after seeing the 4 orthogonal measurements with their 8 corresponding initializations but no initial transfer of classical info, the first thing ...
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What is the computational complexity of decomposing operators in terms of quantum gates?

I have recently worked on a problem involving a rather large Hamiltonian, which I wrote some Python code for its generation following the method in this paper. No when I used qiskits ...
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How are Toffoli and a basis-changing single-qubit gate universal?

The Toffoli and Hadamard gates are universal for quantum computing: you can approximate any unitary up to arbitrary precision with a circuit built from these two gates. This is proved for example by ...
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Is there a convention in quantum circuit diagrams for specific quantum measurements?

Is there a convention in quantum circuit diagrams for specific quantum measurements? For example, how could one express the measurement $|0\rangle \langle 0|$ in a circuit diagram?
James Ellis's user avatar
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Writing circuits in Qiskit using only Clifford and T gates

Is there a way in Qiskit to write my circuit using only Clifford and T gates (CX, S, H, T and I think also $S^\dagger$ and $T^\dagger$)? With the function compile (with aer simulator) it gives me some ...
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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 ...
quantum's user avatar
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Can we have a constant-overhead threshold theorem?

The threshold theorem states that any abstract circuit in BQP can be computed by another polynomial-depth circuit that succeeds in the presence of noise. The original construction from 1996 requires ...
Dudu Ponar's user avatar
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Clifford gates constructed from CNOT, H and S gates

Trying to prove that all Clifford gates can be constructed with CNOT, H and S gates, I'm following the classical path by induction (Nielsen and Chuang, Quantum Computation and Quantum Information -- ...
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Help Implementing a 4-qubit super dense coding algorithm

I am new to quantum computation, I have seen examples of super-dense coding; however, I am struggling in my attempts to scale the 2-qubit system to a 4-qubit, here is a visual of the 2-qubit super-...
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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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How to design a RF-SQUID qubit by Qiskit Metal?

I am now learning how to use Qiskit Metal to design superconducting circuits. I found that there are only several transmon qubits in the library. Can I design an RF-SQUID qubit by using Qiskit metal? ...
qcnewbie23's user avatar
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How to efficiently construct quantum circuits of oracles in multi-target quantum search?

In standard Grover's quantum search with only one target or its extension of multi-target quantum search, one of the two key parts is to quantize the boolean function $$f(x):\{0,1,\cdots,N-1\}\...
Chao-Hua Yu's user avatar
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Feynman method and polynomial time algorithm for XQUATH

Consider the Feynman algorithm for simulating quantum circuits, as given here. Consider the XQUATH conjecture for random quantum circuits from here, given by (XQUATH, or Linear Cross-Entropy Quantum ...
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Query complexity on Quantum Pattern Matching of Mateus Algorithm

I am trying to understand the complexity of the Mateus and Omar algorithm for quantum pattern matching, it is clear to me from the pseudocode that the query complexity is $O(\sqrt{N})$, apart from the ...
Julio César JX's user avatar
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What are some standard ways to visualize non-unitary processes

In quantum computing, quantum circuits are a common model for visualizing unitary evolution. If I want to represent a unitary $U$ acting on a $2$-qubit state $|00\rangle$ followed by a measurement in ...
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What's the circuit to create superpositions corresponding to efficiently integrable probability distributions?

See article here: https://arxiv.org/abs/quant-ph/0208112 There are two steps in this procedure that I am curious about. First off, they suppose one can construct a circuit which efficiently performs ...
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methodology for design quantum circuits according to a given unitary

This is a general question. Given an arbitratry unitary matrix. How to desigin a quantum circuit to implement it? I am not asking for a specific unitary matrix, but for a general methodology to tackle ...
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4 qubit QFT decomposition in the qiskit textbook

I am reading about the quantum Fourier transform (QFT) in the qiskit textbook, but got stuck at the last part of it which shows a decomposed version of the 4 qubit QFT circuit. It seems that the ...
pilsungk's user avatar
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Complexity of the quantum circuits that are needed to implement communication protocol?

Consider the following simultaneous communication problem. Alice and Bob do not share any entanglement or any common randomness, and cannot communicate directly with each other. As inputs, x is given ...
Ruben Hoba's user avatar
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Understanding circuit to Hamiltonian embedding where we do not have a separate clock register

I am trying to understand the clock construction given in this paper, to embed a circuit to a Hamiltonian, which doesn't need to access a separate clock register. The construction, at a high level, ...
BlackHat18's user avatar
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How to construct a quantum circuit that given $|\psi_0\rangle,|\psi_1\rangle$ outputs $\frac{1}{c}(|\psi_0\rangle+|\psi_1\rangle)$?

Suppose I have two arbitrary quantum states $\lvert \psi_1 \rangle $ and $\lvert \psi_2 \rangle$. Further suppose that we know $U_1$ such that $\lvert \psi_1 \rangle = U_1 \lvert 0 \rangle$, but we ...
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Calculate Outputs of a Teleportation Circuit

In this question, I assume we use matrix representation to calculate what each output could be? For example, for the middle qubit in state: $$|00\rangle$$ After the first Hadamard and CNOT gate (so ...
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Defining quantum computer without reference to a classical computer

In the definition of an "efficient quantum computer", there is a uniformity condition that suggests to me that the notion of an efficient quantum computer is not independent of the notion of ...
trillianhaze's user avatar
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Is there a fix for the varying numerical gradients calculated in the optimizer with qiskit?

I am currently trying to train a quantum circuit on Qiskit using an Azure QPU. I have some parameterized gates that I optimize using ADAMs. However, as the output of the circuit $f(x)$ is not ...
Rij's user avatar
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Layout error with after compilation with custom Qiskit pass manager

I am trying to implement the custom Qiskit pass manager from this paper. The code from the authors is provided here on GitHub. I am able to get the pass manager working, and a compiled circuit is ...
greelious's user avatar
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Modelling Mach-Zehnder and saturating Cramer-Rao bound

I am simulating (using Mathematica) a Mach-Zehnder interferometer, with photon counting measurements at the end (based on the setup described in the recent post) for the input state $|\psi\rangle:=|0,...
John Doe's user avatar
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How can i label input and output ports of my QuantumCircuit in qiskit?

I made quantum circuits as quantum gates then later used these gates in a larger circuit. Here, the input ports of the block (which is the gate) are labelled by integers but i want to custom label ...
Syed Shahmir Kazmi's user avatar
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What's a quantum algorithm in the black box model to find $j_1,j_2$ such that $f(x_1,...,x_n)=x_{j1}\oplus x_{j2}$?

Consider the set of all functions $f : \{0, 1\}^n → \{0, 1\}$ that are of the form $f(x_1, x_2, . . . , x_n) = x_{j1}\oplus x_{j2}$ for some distinct $j_1, j_2 \in \{1, 2, . . . , n\}$. Suppose that ...
metaUser's user avatar
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How to build the quantum circuit ansatz to implement a diagonal unitary operator with just 1 and -1 elements?

Let's consider a set of $N = 2^n$ binary values $S_i \in \left\{-1, 1\right\}$ and define the diagonal matrix $W$ as a quantum unitary operator acting on a system of $n$ qubits: $$ W = \begin{pmatrix} ...
SimoneGasperini's user avatar
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Quantum circuit runtime

I want to estimate the execution time of some experiments, and I would be interested to know how the time needed to run a quantum circuit grows in function of the number of qubits and the parametric ...
barrieta's user avatar
2 votes
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160 views

How to roughly analyze computational complexity of quantum circuit?

I'm looking for just a few simple calculations to analyze complexity when comparing quantum circuits. I'll compare 2 scenarios, and I'd love for someone to critique or verify my analysis: Circuit of ...
IsalanOnkar's user avatar
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Can we show that a quantum circuit with Poly(n) gates has a Hamitonian with Poly(n) terms?

It is already known that if the Hamiltonian is a sum of Poly(N) Pauli terms, it has an efficient implementation as a quantum circuit. This should mean that the circuit can be implemented with Poly(N) ...
Kira N's user avatar
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Converting from amplitude encoding to basis encoding

The question is inspired from Preparing a quantum state from a classical probability distribution which shows how basis encoding $\frac{1}{\sqrt n}\sum_{x=0}^{n-1}|x\rangle|p(x)\rangle$ may be ...
Philips's user avatar
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1 answer
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Exact expectation value of a quantum circuit simulated with the matrix product state method in qiskit

If I use the matrix product state method in Qiskit to simulate quantum circuits, I can obtain the exepctation value of an observable by using a finite amount of shots. Is there a way to obtain the ...
stopper's user avatar
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How to use stabilizers to simulate the circuit?

Sorry for this easy questions. That is a simple textbook question but I don't know how to solve it. I have the following circuit: The question was "use stabilizers to simulate the circuit" ...
quest's user avatar
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1 answer
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Qiskit implementation for projecting a hermitian operator and finding its eigenvalues

I'm brand new to quantum computing and have been learning Qiskit for a few weeks now. I am attempting to find the number of 0 eigenvalues of the following operator: $$ T = PHP$$ where $P$ is a ...
pokerfacegoatee's user avatar
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How to simulate these Floquet and Rotation operators for kicked top model?

In this and other papers relating to the kicked top model, it is mentioned that spin coherent states can be expressed as: $$\left|\theta,\phi\right>=R(\theta,\phi)\left|j,j\right>$$ for given ...
akkh's user avatar
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How to detect and correct swap errors in a quantum circuit?

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}(...
Turbotanten's user avatar
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220 views

Is there an efficient quantum circuit that create a random permuntation matrix?

Suppose we want to generate a random, random according to some probability distribution, unitary permutation matrix that is applied to an input of $n$ qubits. So is there an efficient polynomial time ...
Learner's user avatar
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Marginal output probability of first bit for constant-depth circuits

Consider a constant depth $1\text{D}$ quantum circuit, which is applied to the input state $|0^{n}\rangle$, and whose output is measured in the standard basis. You can assume that the gates of the ...
BlackHat18's user avatar
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2 votes
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Iterative Phase Estimation with noise vs standard Quantum Phase Estimation with noise

I am doing Qiskit Lab 4 about Iterative Phase Estimation. I created a circuit implementing IPE for theta = 1/3 (phase of 2pi/3). Here's the circuit: It seems to do okay if I run it without noise in a ...
Mykolas Sveistrys's user avatar
2 votes
2 answers
168 views

Symmetric Universal Quantum Cloning Machine (UQCM) $N \to M$ for unknown states

Does it exist a schematic diagram of the quantum circuit implementing the symmetric UQCM $N \to M$ for unknown states? If yes, does anyone know a Qiskit implementation of it?
L. Lenzini's user avatar
1 vote
0 answers
33 views

Will my custom gate actually spin when I run it on real hardware?

I am trying to create a custom gate using Qiskit Pulse and use it in my quantum circuit. Below is the code I have written so far. ...
Lee's user avatar
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1 vote
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Highly-efficient $n(n+1)$?

Appendix G of this paper provides a highly-efficient way of squaring integer numbers. (LMK if anything more advanced is already available.) I'm wondering if this approach can be easily modified to ...
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1 vote
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A maximally distant unitary from a parameterized circuit

I have a parameterized circuit that includes a certain number of rotation gates, each parameterized by an angle. By sampling over these angles, I can obtain various unitaries. What are the unitaries ...
trurl's user avatar
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1 vote
1 answer
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How to suppress long parameters list that appears in the initialize gate?

Below is a simplified code which I am using for a quantum circuit. ...
Shravan Patel's user avatar
1 vote
0 answers
105 views

How to convert QUBO (with non-zero diagonal elements) to Maxcut?

I want to solve QUBO with non-zero diagonal elements in matrix Q using QAOA. But I want to solve for a large enough problem size (30+ variables) and hence want to divide my circuit into subcircuits. ...
Oleksii's user avatar
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1 vote
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qml.StronglyEntanglingLayers custom CNOT placement

The qml.StronglyEntanglingLayers function works great for what I need. However, I'd like to modify so that for each layer, only the first qubit is the control and the rest are targets of the control ...
TuktukTaxi's user avatar
1 vote
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Action of below circuit using heisenberg representation

Can someone please explain how the above gate affects logical operators? My understanding is that the circle indicates that we are measuring the second qubit? My initial guess is that it is equivalent ...
am567's user avatar
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