Delayed Choice Bell-state Quantum Eraser

[Cthugha]

But, there is no mention of this being done in the delayed choice quantum experiments.

Of course not. At least not in the majority of experiments as they involve double slits. Temporal coherence does not matter for a double slit. A double slit measures spatial coherence. The quantity of interest in this case is momentum. The filtering in momentum space is mentioned. Just have a look at the size of the detectors given in the manuscripts.

edit: As it turns out, I was wrong about this. They do indeed also use a spectral filter, too. From the Walborn paper (PHYSICAL REVIEW A, VOLUME 65, 033818 (2002)):

"The detectors are EG&G SPCM 200 photodetectors, equipped with interference filters (bandwidth
1 nm) and 300 microm X 5 mm rectangular collection slits. A stepping motor is used to scan detector Ds ."

 

[marksesl]

Of course not. At least not in the majority of experiments as they involve double slits. Temporal coherence does not matter for a double slit. A double slit measures spatial coherence. The quantity of interest in this case is momentum. The filtering in momentum space is mentioned. Just have a look at the size of the detectors given in the manuscripts.

edit: As it turns out, I was wrong about this. They do indeed also use a spectral filter, too. From the Walborn paper (PHYSICAL REVIEW A, VOLUME 65, 033818 (2002)):

"The detectors are EG&G SPCM 200 photodetectors, equipped with interference filters (bandwidth
1 nm) and 300 microm X 5 mm rectangular collection slits. A stepping motor is used to scan detector Ds ."

Ok, thanks. I have that paper printed out actually. I'll check it out. So, then this is differently one reason for doing incidence counting, pick out coherent light from the mass of incoherent light made up of the incoherent entangled photons, which are comprised of a spectrum of different wavelength emitted by the BBO crystal.

 

[marksesl]

Has anyone read the description of the double slit experiments on this site? They claim that a detector if left on, but with the recording tape removed will still result in the fringe pattern being restored. I don't believe it. It just can't be.

http://genesismission.4t.com/Physics/Quantum_Mechanics/double_slit_experiment.html

 

[Cthugha]

This is just another try to push new age claims by misinterpreting the experiment. If there is an irreversible interaction at the detector giving which-way information, the fringe pattern will not be visible. It does not matter, whether you destroy the record, do not look at the data or even keep the detector switched off.

 

[rkastner]

I address quantum eraser experiments in some detail in my book, in Chapter 5. I note that these experiments are often hyped and misconstrued as, e.g., 'erasing which-way info after it's already been recorded'. This is not the case. Of course I am applying the transactional picture in my approach, but the basic point holds without that specific interpretation. There is no explicit retrocausality going on here, nothing beyond the usual EPR-type correlations.

QM is strange enough without the efforts on the part of some writers to make it even stranger than it is.