# ZX-calculus : measurement and output probabilities

I'm discovering ZX-Calculus, and it seems to be much easier to do computations on circuit that would take much more time with the usual formalism. However, I can't find a nice way to represent measurements (instead of post-selection) and compute the output probabilities. I have the feeling that normalisation and adding variables to a "one-leg" spiders could help, but I'm not yet convinced that it's the good way to go.

And for example, can ZX-calculus deal with "impossible"/not normalisable circuits, like "create a plus state and project it on minus" ?

Thanks!

• @NieldeBeaudrap No, I had accidentally flagged the wrong post earlier. I rescinded the flag but forgot that it automatically generates that comment. Sorry. – Jonathan Trousdale Feb 6 at 0:45

In the ZX calculus, the closest thing to a graph that measures an observable is a graph that post-selects that observable to be in its $$+1$$ eigenbasis.