  Performing measurements for high-weight operators has been a practical
problem in quantum computation, especially for quantum codes in the stabilizer
formalism. The conventional procedure of measuring a high-weight operator
requires multiple pairwise unitary operations, which can be slow and prone to
errors. We provide an alternative method to passively detect the value of a
high-weight operator using only two-local interactions and single-qubit
continuous measurements. This approach involves joint interactions between the
system and continuously-monitored ancillary qubits. The measurement outcomes
from the monitor qubits reveal information about the value of the operator.
This information can be retrieved by using a numerical estimator or by
evaluating the time average of the signals. The interaction Hamiltonian can be
effectively built using only two-local operators, based on techniques from
perturbation theory. We apply this indirect detection scheme to the four-qubit
Bacon-Shor code, where the two stabilizers are indirectly monitored using four
ancillary qubits. Due to the fact that the four-qubit Bacon-Shor code is an
error-detecting code and that the Quantum Zeno Effect can suppress errors, we
also study the error suppression under the indirect measurement process. In
this example, we show that various types of non-Markovian errors can be
suppressed.
