# Questions tagged [phase-estimation]

Refers to the quantum algorithm used to estimate the eigenvalue corresponding to an eigenvector of a unitary operator. (Wikipedia)

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### Quantum Phase Estimation answers distribution

Suppose I have a random unitary matrix, known eigenvectors and eigenvalues. I know that exact eigenvalue for the given matrix is $0.5491617699847768+0.835716070437315j$. From here, if I'm not mistaken ...
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### How to have seperate registers from scrach?

I am very new to quantum computing, so this might be a really simple question. I am coding a quantum computer simulator in python from scrach and I'm not sure how to make registers work. I would just ...
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### How does the complexity of extracting eigenvalues via quantum phase estimation compare with the classical one?

Suppose, I have ideal quantum computer that allows me to find exact eigenvalues with QPE algorithm under perfect matrix, eigenvectors and eigenvalues conditions. How the complexity of this algorithm ...
1 vote
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### Deriving circuit templates for Hamiltonian simulation

Background I've been reading the paper entitled Some improvements to product formula circuits for Hamiltonian simulation. The authors propose three improvements motivated by phase estimation type ...
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1 vote
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### How to determine the single-qubit phase?

In some works it is suggested to find the qubit phase by the following method: Apply $X/2$ (or $Y/2$) gate - preparing the qubit in superposition. Detune the qubit by flux pulse, for example here ...
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1 vote
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### Can I get valid solution with HHL algorithm even if the QPE is not completely correct?

Can I get the valid solution of linear problem using HHL algorithm even if the QPE is not completely correct? My example is $A=diag(0.5, 0.2, 0.3, 0.6)$, so the solution is $[0.5, 0.2, 0.3, 0.6]$ ...
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### How to estimate the negative amplitude of multiple qubits?

The probability of measurement is the square of amplitude. After measurement, how to guess the original amplitude of state?? For example, in linear problem, we would like to know the exact solution, ...
• 33
1 vote
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### Accuracy of QPE using histogram fit

In regular QPE, accuracy is $1/2^n$, where $n$ is estimation register size, and it is done with few shots and depth as $O(2^n)$ (total cost of $O(2^n*NumShots))=2^n=1/resolution$). I thought of the ...
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1 vote