quantum RCA

I am attempting to build a 2-bit ripple-carry adder, using IBM Quantum Experience composer, but I'm confused on how to construct the carry transpose that is shown at the bottom?


1 Answer 1


The $\dagger$ means inverse. Invert the individual operations within $C$ (they are all self-inverse so this is easy) and then run them in reverse order.

  • $\begingroup$ can I remove it since it does nothing in this case? and do you mean that if I want to implement it then the toffeli gate would be at the end of the carry? $\endgroup$
    – n22
    Apr 1 at 21:22
  • $\begingroup$ @n22 No you can't remove it. Each operation of $C$ is self-inverse, but you still need to run them in reverse order. $\endgroup$ Apr 1 at 21:23

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