# Questions tagged [quantum-fourier-transform]

Quantum Fourier Transform (QFT) is a linear transformation on quantum bits and is the quantum analogue of the discrete Fourier transform. The quantum Fourier transform is a part of many quantum algorithms, notably Shor's algorithm for factoring and computing the discrete logarithm, the quantum phase estimation algorithm for estimating the eigenvalues of a unitary operator, and algorithms for the hidden subgroup problem. (Wikipedia)

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### N-Qubit Hadamard vs Quantum Fourier Transform

Both Simon's algorithm and the algorithm for period finding begin by placing qubits in the equal superposition state, but Simon's algorithm uses the n-qubit Hadamard $H^{\otimes n}$ while the period ...
462 views

### Why after transpiling a Qiskit circuit we obtain a different result?

I am trying to obtain the correct circuit transpiled for the ibmq_london device, as I want to know what the real gates applied in the quantum computer are. I am implementing the QFT circuit for 5 ...
73 views

### QFT on timeseries Data and compare results with classical FFT

Intention - To learn and apply QFT on time-series data and compare the result with classical FFT. Data Used - Small timeseries data of 16 points - ...
126 views

### Is there a quantum operation to change a phase $e^{(0.q_0 q_1 q_2 q_3)}$ into $e^{(0.q_1 q_2 q_3)}$?

Given a set of four qubits, say $q_{0},q_{1},q_{2},q_{3}$ which represent a $4$-bit binary number with $q_{0}$ as the MSB. After applying QFT on these qubits the phase of $q_{0}$using the concept of ...
198 views

### How to find a circuit for the roots of QFT?

After reading about using quantum gates instead of ancillas, it asserts that every quantum circuit has a square root. Theoretically, they do, but is there a practical method to generate the quantum ...
48 views

### Indexing an "unknown" quantum state

Assuming I have a state $$|x\rangle = \frac{1}{\sqrt{n}}\sum_n |x_n\rangle$$ where $|x_n\rangle$ are quantum state vectors $$|x_n\rangle = \frac{1}{\|x_n\|}\sum_i x_{in}|i\rangle$$ and that I have a ...