Craig Gidney

People complain that the "find the cycle in a linked list" interview question is contrived. I thought that too… til I was writing the loop analysis in stim's circuit-to-dem conversion, realized it was analogous, and the standard answer was way better than what I'd been writing.

A circuit compilation exercise. Show that MX+CX+T is a universal gateset by constructing an H gate. MX: X basis measurement CX: controlled NOT T: 45 degree rotation around Z axis (Classical feedback and ancillas is allowed.)

A reminder that if your paper has open data containing stim circuits, I keep a list of those and you can be on the list. I know my 2025 list so far is incomplete: github.com/quantumlib/Sti…

A CPU can add 32bit numbers in a nanosecond. In my quantum factoring estimate, I also used 32bit adders. They're a bit slower. Each superposed add costs TWO MILLION nanoseconds. Quantum factoring isn't fast because of fast operations; it's fast because it uses *few* operations.

Quantum attacks on elliptic curve crypto have costs dominated by one operation: uncomputing a division (see fig15 and fig20 of arxiv.org/abs/2302.06639). Masking makes it easy to *compute* a division, but isn't reversible (arxiv.org/abs/2008.04577). A strange situation. Fixable..?

By when do you think the RSA2048 challenge number will be factored?

And for a great high-level overview, I can whole heartedly recommend this great presentation by Sam Jaques: youtube.com/watch?v=nJxENY…

Mike finally paid for the "pro" version of sketchup, so we owned the 3d models attached to the paper, meaning the yoked surface codes paper is now published! nature.com/articles/s4146… This paper's message is: when people say they're 10x better than surface codes, actually it's 4x.

Nate Soares and I are publishing a traditional book: _If Anyone Builds It, Everyone Dies: Why Superhuman AI Would Kill Us All_. Coming in Sep 2025. You should probably read it! Given that, we'd like you to preorder it! Nowish!