# Delayed choice quantum eraser question

1. Aug 27, 2006

### cornernote

I have a question about the delayed choice quantum eraser with the double split experiment. Forgive me if this is a silly question.

I have seen the following:

TEST 1
1. shoot the particles & measure the result
2. erase the result
3. check the wall (whatever you shot the partical at)
= wall shows inteference pattern

TEST2
1. shoot the particles & measure the result
2. check the result
3. check the wall
= wall shows non inteference pattern

I would like to know the following result:

TEST 1
1. shoot the particles & measure the result
2. check the wall
3. erase the result
4. check the wall again

TEST 2
1. shoot the particles & measure the result
2. check the wall
3. check the result
4. check the wall again

Could you possibly get an inteference pattern at step 2 and then a non inteference pattern at step 4 or vise-versa?

2. Sep 16, 2006

### cornernote

I don't know if bumps are allowed here, but I would really like to know the answer to this question.

3. Sep 17, 2006

### Thrice

Well I personally don't get your question. You need to frame it more precisely & I suspect you misunderstand parts of it. The only thing that changes is your interpretation of "what actually happened."

4. Sep 17, 2006

### cesiumfrog

As far as I understand these experiments, the wall never shows an interference pattern. If you refer back to published results, you should notice that the interference fringes are only in the coincidence data.

5. Sep 18, 2006

### blackwizard

Somethin i figure was weird about that experiment tho. U know which path the particle takes 50% of the time and dont the other 50%. Every time a particle hits the "wall" it makes a mark. U colour in all the marks that u have no which-path info for and they form an interference pattern. If u rubbed them out instead, wouldn't you also get an interference pattern? (Non inteference pattern - inteference pattern = inteference pattern) If so, does this mean the particles that you did get which-path info for still interfere?

6. Sep 19, 2006

### cesiumfrog

Don't think so wiz. Possibilities:
1) slit A: gaussian
2) slit B: gaussian
3) slit A + slit B: fringes
4) slit A - slit B: antifringes

7. Sep 19, 2006

### blackwizard

Awh! If i understand u right, that makes so much more sense. Actually solves a different question that was in my head too! Brian Green didnt mention u had to seperate the marks u dont hav which path info for in2 3 & 4 to get the patterns.

Are 3 & 4 the 2 different "no-which-path" detectors? Or hav i completely misinterpreted ur post

8. Sep 24, 2006

### cesiumfrog

Yes, that seems to be the experimental result, maybe someone else could explain the theory behind those two different versions of "no-which-path"?