Hello,

*Context:*

*I am trying to build an architecture that contains a feedback loop of a wire (with the strawberryfields.fock plugin). Every iteration, an input gets combined with a feedback state, after which it gets fed into a reservoir. Also every iteration, part of the reservoir output gets measured and part of the reservoir output gets feedbacked.*

To combine the input state with the feedback state, I need **some kind of combiner**. For example (with 3 wires): if `psi_in = [0,1,0]`

and `psi_fb = 1/sqrt(2) [1,0,0] + 1/sqrt(2) [0,1,0]`

, I want the result `psi_combined = 1/sqrt(2) [1,1,0] + 1/sqrt(2) [0,2,0]`

.

In practice, I would do this with a `2x1 multimode interferometer (MMI)`

. Is there some way to achieve this in PennyLane?

In StrawberryFields I thought about coupling the correct wires and using **post-selection**, but I can’t seem to use post-selection in PennyLane. Is that correct?

Kind regards and thanks in advance,

Robbe