Hi,
I was wondering if it is possible to define (in Gaussian formalism) spatial mode vectors whose elements are annihilation (creation) operators representing various spectral modes, corresponding to a pair of spectrally impure photons with Schmidt number different from 1. Furthermore, I’m also interested to know if it’s feasible to define a frequency-dependent beam splitter (BS) with transmission and reflection coefficients that vary with frequency.
Bests,
Hey @ekccagin! Welcome back 
I’m honestly not sure. I’ll have to consult an expert here. Hang tight and I’ll get back to you as soon as I can!
Hey @ekccagin, I heard back from one of the experts here. Here’s what they said:
Dealing with spectral modes - We have a branch/PR in thewalrus called internal modes (work in progress) about spectral modes which you may or may not find helpful.
Frequency-dependent beamsplitters - We don’t currently do this but I think you could define your own symplectic matrices similar to this function except in the loop over the spectral modes you would change the U to be the different beamsplitter unitaries.
To piggy-back on their response, I do recommend that you stay away from the PennyLane-Strawberryfields plugin unless you absolutely require something there. We’re no longer maintaining that plugin. Other photonic quantum computing software options that we provide are:
Let me know if this helps!