Source code for toqito.rand.random_states

"""Generates random quantum states using Qiskit."""

import numpy as np




def random_states(n: int, d: int, seed: int | None = None) -> list[np.ndarray]:
    r"""Generate a list of random quantum states.

    This function generates a list of quantum states, each of a specified dimension. The states are
    valid quantum states distributed according to the Haar measure.

    Examples:
        Generating three quantum states each of dimension 4.

        ```python exec="1" source="above"
        from toqito.rand import random_states

        states = random_states(3, 4)
        print(f"length of states is {len(states)}")

        print(f"Shape of each state vector: {states[0].shape}")

        for idx, state in enumerate(states):
           print(f"\nState {idx}:")
           print(state)
        ```

        It is also possible to pass a seed to this function for reproducibility.

        ```python exec="1" source="above"
        from toqito.rand import random_states

        states = random_states(3, 4, seed=42)

        for idx, state in enumerate(states):
           print(f"\nState {idx}:")
           print(state)
        ```





    Args:
        n: int The number of random states to generate.
        d: int The dimension of each quantum state.
        seed: int | None A seed used to instantiate numpy's random number generator.

    Returns:
        A list of `n` numpy arrays, each representing a d-dimensional quantum state as a column vector.

    """
    gen = np.random.default_rng(seed=seed)
    samples = gen.normal(size=(n, d)) + 1j * gen.normal(size=(n, d))
    samples /= np.linalg.norm(samples, axis=1)[:, np.newaxis]
    return [sample.reshape(-1, 1) for sample in samples]