Clarification on "Bob must do the same thing to every pair of electrons" in Quantum Computing for Everyone (Superdense Coding)

Clarification on "Bob must do the same thing to every pair of electrons" in Quantum Computing for Everyone (Superdense Coding) Ask Question Asked 5 months ago Modified today Viewed 110 times 4 I am reading Quantum Computing for Everyone Quantum Computing for Everyone by Chris Bernhardt and I came across the following passage in the section on Superdense coding Superdense coding : Alice and Bob initially have one electron each. Eventually, Bob is going to have both electrons and is going to measure their spins. Bob will have some quantum circuit with two wires exiting. If Alice wants to send 00, we need to arrange things so that just before Bob starts measuring, the top electron is in state |0⟩ | 0 ⟩ and the bottom electron is in state |0⟩ | 0 ⟩ , that is, the pair of electrons is in the unentangled state |00⟩ | 00 ⟩ just before Bob measures their spins. Similarly, if Alice wants to send 01, we want the pair of electrons to be in the state |01⟩ | 01 ⟩ just before Bob makes his measurements. The final state should be >|10⟩ > | 10 ⟩ if Alice wants to send 10, and |11⟩ | 11 ⟩ if Alice wants to send 11. I follow this part, but the next paragraph confuses me: The final observation is that Bob must do the same thing to every pair of electrons that he receives. He cannot do different things depending on what Alice is trying to send, because he doesn’t know what she is trying to send. That’s the whole point! Could anyone please elaborate on what it means that "Bob must do the same thing same thing to every pair of electrons that he receives. He cannot do different things different things "? measurementcommunicationsuperdense-codingquantum-information Share Improve this question Follow asked Oct 27, 2025 at 16:23 seeker 2511 1 silver badge 5 5 bronze badges Related post. –  Flint Commented Feb 8 at 10:07 Add a comment 1 Answer Sorted by: Highest score (default) Date modified (newest first) Date created (oldest first) 0 It probably means that Bob has to perform the same circuit for each pair - namely, CNOT controlled by the qubit sent by Alice onto the qubit held by Bob, then Hadamard on the qubit held by Bob, and measure both elements of the pair in the computational basis. It's probably just meant to emphasize that all of Bob's actions are local to him, with no further communication from Alice. Share Improve this answer Follow answered Oct 27, 2025 at 17:18 community wiki Mark Spinelli Add a comment Your Answer Sign up or log in Sign up using Google Sign up using Email and Password Post as a guest Name Email Required, but never shown Post Your Answer By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy. Start asking to get answers Find the answer to your question by asking. Ask question Explore related questions measurementcommunicationsuperdense-codingquantum-information See similar questions with these tags. 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