Phase estimation ยท Circuits
Semiclassical quantum Fourier transform
Theorem statement
Let $n\geq1$, $N=2^n$, $\omega=e^{2\pi i/N}$,
and $\ket{\psi}=\sum_{j=0}^{N-1}\alpha_j\ket{j}$
be an $n$-qubit state.
There exists an $n$-qubit quantum circuit using at most
$n$ Hadamard gates, $n(n-1)/2$ single-qubit phase gates and $n$ classical bits to
obtain a classical output $k\in\{0,\ldots,N-1\}$ with distribution
$$
\Pr[k]
=
\frac{1}{N}
\left|\sum_{j=0}^{N-1}\alpha_j\omega^{jk}\right|^2.
$$
Sources
- Semiclassical Fourier Transform for Quantum Computation
Robert B. Griffiths, Chi-Sheng Niu, 1996
Lean context
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