Delayed-choice · quantum eraser · two files
Delayed-choice quantum eraser showed stripes after they hid which path.
You heard delayed-choice quantum eraser rewrites the past. You came to see how the lab ran it.
Delayed-choice quantum eraser is a light test. A later measurement decides whether you can still tell which path, then you look at the matching pairs.
They already recorded one click.
Then they hid which path on some pairs, kept which path on the others, and sorted those matching pairs into two files you can look at side by side.
Two linked bits of light
Kim, with Yu, Kulik, Shih, and Scully, printed this in 2000 in Physical Review Letters under the title Delayed Choice Quantum Eraser, so you can find the same file they printed.
They used a photon-pair test, which means two linked bits of light. One bit hit a detector early, and its twin took a longer path and faced a later measurement.
Which path means which of two routes that twin could take. They recorded the early click first, then they ran the later measurement after the extra path, so the later measurement came after the first click was already on the record.
Read the paper at doi.org/10.1103/PhysRevLett.84.1 and at arxiv.org/abs/quant-ph/9903047.
Kim's group ran light. They did not run people through a trial.
Hide which path and you get stripes
When they sorted pairs by the later measurement that hides which path, those files showed stripes, the bright and dark bands people call interference or fringes, sitting on the file where you can see them.
When they kept which-path, those files stayed flat. The early clicks were the same. The sort is what changed the picture.
You can hold both files in your head at once, stripes on the hidden-path pairs and a flat line on the which-path pairs. The itch comes because they already recorded the early click before they sorted.
Keep the rewrite hunger
You already brought rewrite-the-past to this page. Keep that hunger. The lab still prints two files when they sort the matching pairs.
Someone sold a cartoon of this test and hid the sort, the two-file split that lets you see stripes on one pile and a flat line on the other. Look at both files. That is how they ran the light.
Later different work from Ma's group in 2013 ran longer paths in Vienna and the Canaries, and those notes sit in the sources card. The 2000 light test is the story on this URL.
If you want a page about a deep absorption in a scanner, open the jhana page. If you want a twelve-minute chant with a brain scan, open the Kirtan Kriya page. More files sit in the Library.
Questions people ask when they see the stripes
Did the past change?
Keep wanting rewrite-the-past. The paper shows how they sorted the pairs, and the hidden-path pairs show stripes while the which-path pairs stay flat.
Do I need people in a trial?
Kim's group ran light on two linked bits of light, and they did not run a human trial.
What do I do with the rewrite hunger?
Keep it. Sit with the two files. Do not invent a promise the paper never printed.
Sit with the two files this week
This week, sit with the two files. Hidden-path pairs show stripes. Which-path pairs stay flat.
You came because you wanted the past to move. Keep that hunger, look at the sort they printed, and leave the week holding both pictures, the striped file and the flat file, without asking the paper for a promise it never wrote.
If you need care, call a doctor you trust.
Sources
Kim Y.-H., Yu R., Kulik S.P., Shih Y.H., Scully M.O. “Delayed Choice Quantum Eraser.” Phys. Rev. Lett. 2000;84(1):1-5. DOI 10.1103/PhysRevLett.84.1. PMID 11015820. Optical delay about 2.5 m / 8 ns, R01 and R02 fringes, R03 and R04 flat, later measurement labels which coincidence pairs you kept, photon-pair coincidence, no human trial n. doi.org/10.1103/PhysRevLett.84.1 · arxiv.org/abs/quant-ph/9903047
Ma et al. 2013 PNAS, later different work, Vienna 55 m, I=0.955(7), V=0.951(18), Canaries 144 km.