Does sending a qubit using a quantum network through some conventional physical medium mean it is not with sender anymore after sending?

Question

I was reading the wiki page on superdense coding algorithm. I am not quite sure what happens in this algorithm. When the photon which is part of entangled pair is being sent to Bob from Alice's side, does that mean that photon is not there with Alice anymore?

(I am asking this because if it is not there then to send some classical information again, we have to prepare another entangled pair or Bob has to send back that photon. Because upon projective measurement in bell basis the state won't be destroyed.)

Answer 1

Yes, your understanding is correct: when Alice sends her qubit to Bob, she doesn't have that qubit any longer. Entangled pairs of qubits distributed between the parties are a resource that is used up: sending 2 classical bits of information uses up one pair, and this pair cannot be reused to send another 2 bits without extra steps (like you suggested, Bob could send the qubit back).