# Questions tagged [quantum-algorithms]

For questions about quantum algorithms, that is, sequences of quantum gates, operations, and measurements, whose purpose which achieve some goal. Standard examples are Shor's and Grover's algorithms.

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### Grover's Algorithm: Why is the amplitude of $\left|a_{0}\right>$ after the second iteration $\frac{1}{\sqrt{N}}(5-\frac{20}{N}+\frac{16}{N^{2}})$?

Grover's Algorithm: Why is the amplitude of $\left|a\right>$ after the second iteration $\frac{1}{\sqrt{N}}(5-\frac{20}{N}+\frac{16}{N^{2}})$? If I apply the Grover operator twice to the initial ...
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### What is a universal quantum algorithm?

Nobody seems to define the term anywhere. It's in the abstract of "Factoring integers with sublinear resources on a superconducting quantum processor" by Bao Yan, Ziqi Tan, Shijie Wei et ...
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### Implementation of QAOA to solve version of knapsack problem

Say I want to fill a knapsack with as many things as possible. I don't care about what they are, simply the number. But I don't want the total weight to exceed a set limit. [https://qiskit.org/...
1 vote
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### Why can Pauli channels be simulated efficiently?

Why can Pauli channels be simulated efficiently on a classical computer (for the purpose of noise simulation)? Could you please help me get an intuitive understanding and also point me to some ...
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### Is Shor demonstration wrong?

in Polynomial-Time Algorithms for Prime Factorization and Discrete Logarithms on a Quantum Computer by Peter W. Shor (also in Algorithms for quantum computation: discrete logarithms and factoring). In ...
1 vote
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### Confusing notation in Block-Encoding

I'm reading the lecture notes from Ronald de Wolf and got confused at the part where it introduces Block encoding, specifically by this notation at page 76: More generally we can define an $a$-qubit ...
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### Implementing Grover's algorithm on 4 qubits

I have the below Oracle function. Below are the marked states for this Oracle function. I wanted to implement Grover's algorithm on 4 qubits. I've been following the below Qiskit notebook: https://...
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### Ancilla intuition, when to use them, how to recognize when I'd want to use them?

Sorry if this is too open ended. I've spent some time studying some various quantum algorithms that involve ancillary qubits. Some examples that come to mind are phase estimation, linear combination ...
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### Quantum Computing Daily Practice / Quiz platform

I am looking for a platform where I can solve quizzes and programming / algorithmic challenges related to quantum computation and information. To be more specific, I am looking for a platform that is ...
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