Polarizing beam splitter with creation/annihilation operator

[elaug...@gmail.com]

Dear all,

I am very new to Qutip and I am trying to model a system with several polarizing beam splitters at which 2 and 4 photons interfere, respectively.

According the documentation of an older version of Qutip, creation and annihilation operators that distinguish between polarizations of the photons used to exist. Now, I cannot find it.

To begin with, I just want to model HOM interference but my task is actually to model the system described in this scheme (or see attached paper).

I have tried other methods (see my questions here and here) and have now retrieved to using creation and annihilation operators.

Does anyone have a good idea as to how I can implement this using Qutip?

Best regards,

Ela