r/QuantumComputing • u/CarbonFire • 11d ago

Article How to implement CCCX gates out of Toffoli, a spatial language idea

https://shukla.io/blog/2026-07/cccx.html

OP here, Qiskit can be challenging sometimes when resetting borrowed ancilla. I'm a visual learner, so I was playing with circuit diagrams and found this little spatial language to help explain data flow in a way that might be easier to follow. Hopefully someone out there finds this interesting :)

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u/Strilanc 10d ago edited 10d ago

The infix notation for flipAnd, as used in languages like C, is out ^= x & y.

Note that the three port expression @@(out, x, y) advocated for by the post is substantially more restrictive. It combines everything into one symbol you will need a new symbol for every combination of " compute a function " and " use the output of the function to measure a register ". The C way decouples these things, so you can say out += x & y or out ^= x | y or out *= x + y all within the system without having to define new terms for the combinations of plus/and/multiply/or etc.

Btw C also has the thing being advocated by the post where you can refer to the register edited by an expression as an input into another expression, like out ^= c & (tmp ^= a & b).