Estimation ยท Algorithms
Amplitude estimation
Theorem statement
Let $0<\epsilon\leq1$, $0<\eta\leq1$,
$n_a=\lceil\log_2(\pi/(\epsilon\eta))\rceil$,
$k=2^{n_a}-1$ and $0<p<1$ such that $p(1-p)=\Omega(1)$.
Consider an $n$-qubit state-preparation oracle $U$ such that
$U\ket{0}=\sqrt{p}\ket{\psi_1}+\sqrt{1-p}\ket{\psi_0}$,
and a reflection oracle $R_1=I-2\ket{\psi_1}\!\bra{\psi_1}$
for some orthogonal states $\ket{\psi_0}$ and $\ket{\psi_1}$.
Given access to $U$, $U^\dagger$ and controlled-$R_1$,
there exists a quantum algorithm that estimates $p$
to precision $\epsilon$ with failure probability at most $\eta$,
using at most $n+n_a$ logical qubits,
$k+1$ queries to $U$, $k$ queries to $U^\dagger$,
$k$ queries to controlled-$R_1$, and the following gate counts:
$$
\begin{array}{c|ccc}
n & \text{Toffoli gates} & \text{CNOT gates}
& \text{Single-qubit gates} \\ \hline
1 & 0
& n_a(n_a-1)+3\lfloor n_a/2\rfloor+k
& n_a(3n_a+1)/2+2k \\
2 & k
& n_a(n_a-1)+3\lfloor n_a/2\rfloor
& n_a(3n_a+1)/2+7k \\
3 & 4k
& n_a(n_a-1)+3\lfloor n_a/2\rfloor
& n_a(3n_a+1)/2+9k \\
4 & 10k
& n_a(n_a-1)+3\lfloor n_a/2\rfloor
& n_a(3n_a+1)/2+11k \\
n\geq5 & 8(n-3)k
& n_a(n_a-1)+3\lfloor n_a/2\rfloor
& n_a(3n_a+1)/2+(2n+3)k
\end{array}
$$
Sources
Lean context
- Lean declaration
QuantumAlg.AmplitudeEstimation.main
Copy a short prompt with the import, theorem name, citations, and public source link.