Delayed choice quantum eraser!
My mind was blown before I even watched it!

My brain hurts!

(July 12, 2020 at 4:30 am)izebo-the-fat Wrote: My brain hurts!

even before it was shown it’s limits.

Sigh.

The problem is that people want to use classical notions, such as waves and particles, as opposed to the actual quantum description.

All *quantum* effects go forward in time. This is true even in the quantum eraser. But, if you insist on thinking of things classically, the results will appear paradoxical.

All paths of the quantum eraser need to be taken into account, including phase information. And, yes, if 'which path' information exists, then no interference pattern occurs. And if 'which path' information is not, then a pattern is seen. This is well modeled in QM and with only forward influences in time.

How is this news? Asimov published ‘On The Endochronic Properties Of Resubliminated Thiotimoline’ more than 70 years ago.

Boru

(July 12, 2020 at 6:33 pm)BrianSoddingBoru4 Wrote: How is this news? Asimov published ‘On The Endochronic Properties Of Resubliminated Thiotimoline’ more than 70 years ago.

Boru

Resubliminated

(July 12, 2020 at 8:31 pm)Fireball Wrote:

(July 12, 2020 at 6:33 pm)BrianSoddingBoru4 Wrote: How is this news? Asimov published ‘On The Endochronic Properties Of Resubliminated Thiotimoline’ more than 70 years ago.

Boru

Resubliminated

Whups. Good catch.

Boru

(July 12, 2020 at 12:14 pm)polymath257 Wrote: Sigh.

The problem is that people want to use classical notions, such as waves and particles, as opposed to the actual quantum description.

All *quantum* effects go forward in time. This is true even in the quantum eraser. But, if you insist on thinking of things classically, the results will appear paradoxical.

All paths of the quantum eraser need to be taken into account, including phase information. And, yes, if 'which path' information exists, then no interference pattern occurs. And if 'which path' information is not, then a pattern is seen. This is well modeled in QM and with only forward influences in time.

'particle' and 'wave' (classical) I agree they are metaphors which have properties that relate to tangible things we experience 'classically' - water wave, sound wave, projectile etc where the waves are in fact series of particles acting on each other. experimental results show that whatever the 'particles' are at a fundamental level they display properties that relate to things we can perceive and illustrate - eg. a photon, or electron, interacts with the back screen in the double slit experiment and leaves a mark such as that we would expect if we launched a tennis ball at it.

but the 'wave function' is a different beast. it dictates the range of potential properties of the particle which only becomes reality when it is 'measured' ie interacts with the environment. where we see interference, we also see that photons arrived as quantized energy chunks, but their distribution is dictated by the wave function in the absence of the which-path information.

Another aspect of the quantum eraser experiment is that the interference patterns only appear when the results from different detectors are compared. If you only look at one detector, there is no interference pattern seen. But, if you correlate the detectors, considering when there are linked detections, the interference pattern forms.

(July 13, 2020 at 10:33 am)polymath257 Wrote: Another aspect of the quantum eraser experiment is that the interference patterns only appear when the results from different detectors are compared. If you only look at one detector, there is no interference pattern seen. But, if you correlate the detectors, considering when there are linked detections, the interference pattern forms.

the interference pattern breaks down and we now have a particle distribution. this may have been interpreted as the detectors physically interfering with the photons and breaking the wave properties. but the effect is the same even when just one detector is placed over one slit. this shows that if it is known that a photon went through one slit then we have that information, but also it is known when particles that did not go through that one slit, they must have gone through the other one that does not have a detector! clever stuff. but there was still some uncertainty over what was happening. then with new technology allowing for particles to be split into entangled pairs, thereby both partners each carrying the which path information, applied to the delayed choice quantum eraser set up, it became possible to put the detectors behind the double slit thereby showing for certain that the act of observation itself is not physically interfering with the photons.