Return the Bures angle between mixed quantum states

    Note: Bures angle cannot be calculated within the tensor backend.

def bures_angle(rho0: Density, rho1: Density) -> float:
    """Return the Bures angle between mixed quantum states

    Note: Bures angle cannot be calculated within the tensor backend.
    """
    return np.arccos(np.sqrt(fidelity(rho0, rho1)))