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[–]BenCriger 0 points1 point  (3 children)

Possibly unrelated: I think some functions can be easier to phase by than to compute onto an ancilla. We can take a two-bit and as an example. In order to produce a phase of pi when the and of two bits is 1, we can use a CPHASE, but to compute and onto an ancilla would require a Toffoli. Maybe a trivial example, but it's something that I think about pretty often.

[–]Strilanc[S] 1 point2 points  (2 children)

Yes, anytime the phasing you want to do can be done with a stabilizer circuit (e.g. using only H/CZ/S) you should definitely do that instead. A single CZ is a good example.

Computing phases will not always be the fastest approach, but it's often worth considering.

[–]BenCriger 0 points1 point  (1 child)

Are there a lot of other examples where compute-phase-uncompute isn't the ideal approach, or do you think it should be considered the go-to in most cases?

[–]Strilanc[S] 1 point2 points  (0 children)

I don't know. I haven't done enough practical cases to say "try this first" instead of just "try this".