-2
$\begingroup$

If I know what oracle to implement, I know what is the state that I am searching for, so why should I use this algorithm?

I mean, if my quantum control system knows how to implement the oracle, it should know how to just encode the specific target state.

Let's look at an example, I want to find the state 0010. I implement the algorithm with this circuit: enter image description here this circuit is equivalent to enter image description here

But, all the Hadamard and CCCZ gates end up to be approximately unity so actually all I am really doing is flipping the second qubit.

Overall, I could just flip the second qubit and find the state with a single gate.

Improve this question
$\endgroup$
2
  • 4
    $\begingroup$ Welcome to QCSE. Have you taken a look at these posts? Post1, Post2 and Post3. If yes, maybe edit your question to be more specific as to what you are still unsure about. $\endgroup$ Commented Mar 24 at 3:27
  • $\begingroup$ Here is an discussion on how to construct oracle for solving QUBO problems without knowing a solution ex ante: quantumcomputing.stackexchange.com/questions/30024/… $\endgroup$ Commented Mar 24 at 7:34

1 Answer 1

Reset to default
4
$\begingroup$

I think a good example here is a 3-SAT problem. For instance, think about an example of finding sets of answer that satisfy all those conditions :

(𝐴∨𝐵∨𝐶)∧(𝐴∨𝐵∨¬𝐶)∧(𝐴∨¬𝐵∨𝐶)∧(𝐴∨¬𝐵∨¬𝐶)∧(¬𝐴∨𝐵∨𝐶)∧(¬𝐴∨𝐵∨¬𝐶)∧(¬𝐴∨¬𝐵∨𝐶)

You make an oracle by simply putting all those conditions together, here you don't necessarily have to know the answer as it's given by the algorithm. Input every possible state to oracle by superposition then grover's search automatically finds the answer by phase flip and amplitude amplification in $O(\sqrt{N})$. enter image description here

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.