> ## Documentation Index
> Fetch the complete documentation index at: https://prod-mint.classiq.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Amplitude Estimation

Functions:

| Name                   | Description                       |
| ---------------------- | --------------------------------- |
| `amplitude_estimation` | \[Qmod Classiq-library function]. |

### amplitude\_estimation

<pre><code>amplitude\_estimation(
oracle: QCallable\[QArray\[QBit]],
space\_transform: QCallable\[QArray\[QBit]],
phase: QNum,
packed\_vars: QArray\[QBit]
) -> None</code></pre>

\[Qmod Classiq-library function]

Estimate the probability of a state being marked by the operand `oracle` as a "good state."

The algorithm prepares the state in the `packed_vars` register and estimates the probability of this state being marked by the oracle as a "good state."
This is done using the Quantum Phase Estimation (QPE) algorithm, where the unitary for QPE is the Grover operator, which is composed of the `oracle` and `space_transform` operators.

**Parameters:**

| Name              | Type                      | Description                                                                                                                                                                                                  | Default    |
| ----------------- | ------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ | ---------- |
| `oracle`          | `QCallable[QArray[QBit]]` | The oracle operator that marks the "good" state. This operator should flip the sign of the amplitude of the "good" state.                                                                                    | *required* |
| `space_transform` | `QCallable[QArray[QBit]]` | The space transform operator (which is known also the state preparation operator), which is first applied to prepare the state before the QPE, and then used inside the Grover operator.                     | *required* |
| `phase`           | `QNum`                    | Assuming this variable starts from the zero state -this variable output holds the $phase=\theta$ result in the \[0,1] domain, which relates to the estimated probability $a$ through $a=\sin^2(\pi \theta)$. | *required* |
| `packed_vars`     | `QArray[QBit]`            | The variable that holds the state to be estimated. Assumed to be in the zero state at the beginning of the algorithm.                                                                                        | *required* |