I am interested in photonic computing, and I am curious how the gates work. I once saw a picture of a photonic CNOT gate that used just mirrors and polarizers. I have not been able to find any blueprints or schematics for working photonic gates.
$\begingroup$ Hi. Each post should contain a single, laser-focused question. I thus removed the last bit of the post. Feel free to ask it as a separate question (providing more context and details as to what you understand about that particular subject). Also, could you add the "picture" you saw? There are different possible ways to realise quantum gates with photonics systems, so that would help pinpointing what exactly you are thinking about $\endgroup$– glS ♦Nov 30, 2020 at 11:14
$\begingroup$ Did the gate work with postselecting the desired state? Or did it include trapped ions in cavities? From the information in your question alone I doubt this gate did what you think it did. $\endgroup$– M. SternNov 30, 2020 at 12:21
1$\begingroup$ @Spock There is an example of a photonic CNOT gate explained in some detail here: quantumcomputing.stackexchange.com/a/8521/8623 $\endgroup$– Jonathan TrousdaleNov 30, 2020 at 13:56