def _stinespring_to_operator(data, input_dim, output_dim):
    """Transform Stinespring representation to Operator representation."""
    trace_dim = data[0].shape[0] // output_dim
    if data[1] is not None or trace_dim != 1:
        raise QiskitError(
            'Channel cannot be converted to Operator representation')
    return data[0]
Transform Stinespring representation to Operator representation.