Optional arguement for observe

[stewa668]

I am doing some work that involves using the jordan-wigner transformation for representing electrons in a molecular system, and also implementing noise models on top of it.

The sum of the binary representation of the computational basis must be equal to the number of particles by definition in my case, but noise can cause final z-basis measurements that would correspond to having the wrong number of electrons. In my case, I got around this issue by getting counts from the observable function, from a new Hamiltonian composed of only N body operators, using only final measurements which have the correct conditions. I was wondering if a similar functionality can be baked into the code somewhere to allow for this to be done with less of a headache. Something like the following features?

1. When using observe, allow for canonicalized versions of the operator to be measured instead of the simpler form that observe turns it into. So, make it so that if IZIZ is passed as an operator to analyze, all 4 qubits could be measured and counted, as opposed to just 2.

2. If the first is done, would it then be possible to make it conditional? As in, throw away all N-body measurements that are not provided in a list of "acceptable" measurements.

If these are already features I am unaware of, or if there is intrinsic reasons this couldn't be implemented, please let me know. Other than that, I think it would be neat. Like a conditional observable. (Which may appear experimentally, if there are results that could only be the result of noise error.)