Sometimes you realise that you are understanding advanced topics while at the same time totally suck at some conceptual understanding. It feels so stupid to ask people for help. Afraid that they will think 'You know so little, you will never be able to accomplish something in this field'.

But well, we don't get wiser otherwise. So here we go with the stupid question I don't know an answer to yet (May 20th, 2022):

1. If a photon went through a beamsplitter, is it then in superposition both at the paths, as within its own probability wavefunction?

2. Will those superpositions always collapse together? Or can it collapse to one path and you still see an interference pattern after the double slit?

Update May 30th, 2022:

I asked a colleague and they provided me with an answer:

1. 'Yes, after the beamsplitter the photon is in superposition both at the paths and within its own probability function.'

2. 'No they will not always collapse together. When you measure at path B and it collapses to path A, the uncertainty of the position of that particle remains. So in that case you will always see the interference pattern. '

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