# How to find all marked items by quantum search algorithm(Grover's algorithm)?

We know that the Grover algorithm outputs a marked item. Now we want to know the locations of all items. I can't find any paper to solve this problem.

## 1 Answer

Grover's search returns a uniform superposition of all marked items. So, yes, in your last step, you measure it and find a random sample out of that set. If you want others, just repeat and you'll get another random sample.

If you want to be a bit more directed, you can explicitly exclude any items you've previously found by unmarking them in your oracle step.

• Repeat will take at least $M$ more 'experiments', so the $O(\sqrt{N/M}$ becomes $O(\sqrt{NM})$, where $M$ stands for the number of right answers and $N$ stands for the total numbers of items to be searched. So unmark might be the only choice now... I think. Jun 30 '21 at 14:21