Why is the Hadamard gate named after Hadamard?

Why is the Hadamard gate named after Hadamard? Ask Question Asked 2 days ago Modified yesterday Viewed 169 times 2 Why is the Hadamard gate H= 1 2 – √ ( 1 1 1 −1 ) 𝐻 = 1 2 ( 1 1 1 − 1 ) named after Jacques Hadamard? Does it have something to do with Hadamard using this kind of (geometrical?) transformation? Who first named it after him? terminology-and-notationhadamardhistory Share Improve this question Follow edited yesterday Martin Vesely 15.6k4 4 gold badges 34 34 silver badges 77 77 bronze badges asked 2 days ago Geremia 1437 7 bronze badges Which came first: the gate or the man? –  QuantumBeef Commented 2 days ago @QuantumBeef I assume Hadamard (1865-1963). –  Geremia Commented 2 days ago Add a comment 1 Answer Sorted by: Highest score (default) Date modified (newest first) Date created (oldest first) 3 According to Wikipedia's page on the Hadamard matrix [page link], Sylvester proposed matrices of the Hadamard form in 1867[Slyvester's paper]. It is later remarked in a paper from Hedayat and Wallis [Hedayat-Wallis paper] on page 1187 'This is why the name "Hadamard matrix" has been used' in reference to previous work on specific matrices from Hadamard himself. I assume the naming suggested in the Hedayat-Wallis paper stuck, if not already being used elsewhere. Share Follow answered 2 days ago QuantumBeef 1065 5 bronze badges 1 Nice answer. For completeness, perhaps you can add a paragraph or so summarizing what Hedayat and Wallis say on p.1187, to fully answer the question "why Hadamard"? –  DanDan面 Commented yesterday @DanDan面 I added some fuller context. –  Geremia Commented yesterday @Geremia I am not seeing an edit? –  DanDan面 Commented yesterday @Geremia: To edit other users posts, you have to have enough reputation. If you do not, your edit must be approved by other users with higher reputation. I have approved it and now you need to wait for approval from other two such users. By the way, nice improvement, you could have considered to post it as your own answer. –  Martin Vesely Commented 2 hours ago 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 terminology-and-notationhadamardhistory See similar questions with these tags. The Overflow Blog What it takes to be a player in the international AI... Making the OWASP top ten in the vibe code... 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