<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def default_channel_ops(nqubits):
 """ Generate the tomographic pre- and post-rotations of any number of qubits as qutip operators. :param int nqubits: The number of qubits to perform tomography on. :return: Qutip object corresponding to the tomographic rotation. :rtype: Qobj """

    for gates in cartesian_product(TOMOGRAPHY_GATES.values(), repeat=nqubits):
        yield qt.tensor(*gates)