Return the all-zero state on N qubits

def zero_state(qubits: Union[int, Qubits]) -> State:
    """Return the all-zero state on N qubits"""
    N, qubits = qubits_count_tuple(qubits)
    ket = np.zeros(shape=[2] * N)
    ket[(0,) * N] = 1
    return State(ket, qubits)