A discussion of effect before cause somehow seem incomplete in a quantum physics forum if the paradox of delayed choice quantum erasure is omitted from the discussion. In this context, numerous delayed choice quantum erasure experiments have been conducted and are reported in the literature (See generally http://en.wikipedia.org/wiki/Quantum_eraser;
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser and
http://en.wikipedia.org/wiki/Wheeler's_delayed_choice_experiment).
In their “
peer reviewed” paper, “Random Delayed-Choice Quantum Eraser via Two-Photon Imaging” (The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics, Volume 44, Number 1 / July, 2007 (see also
http://arxiv.org/abs/quant-ph/0512207v1), the authors: Giuliano Scarcelli, Yu Zhou, Yanhua Shih; provide a brief summary of such experiments and report on their experimental contribution to this literature. For those who are not familiar with these experiments, I have copied their introduction below:
“Quantum erasure was proposed in 1982 by Scully and Druhl [1]. After two decades the subject has become one of the most intriguing topics in probing the foundations of quantum mechanics [2,3]. The idea of quantum erasure lies in its connection to Bohr’s principle of complementarity [4]: although a quantum mechanical object is dually particle and wave; its particle-like and wave-like behaviors cannot be observed simultaneously. For example, if one observes an interference pattern from a standard Young’s double-slit interferometer by means of single-photon counting measurement, a photon must have been passing both slits like a wave and consequently the which-slit information can never be learned. On the other hand, any information about through which slit the photon has passed destroys the interference. In this context Scully and Druhl showed that if the which-slit (which-path) information is erased, the interference pattern can be recovered; the situation becomes extremely fascinating when the erasing idea is combined with the delayed choice proposal by Wheeler and Alley [5,6]: i.e. even after the detection of the quantum itself, it is still possible to decide whether to erase or not to erase the which-path information, hence to observe the wave behavior or the particle behavior of the quantum mechanical object.
In the past two decades, a number of experiments demonstrated the quantum eraser idea by means of different experimental approaches and/or different point of theoretical concerns [7–17]; in particular Kim et al. [12] have realized an experiment very close to the original proposal by using entangled photon pair of spontaneous parametric down-conversion (SPDC). The experiment demonstrated that the which-path information of a photon passing through a double-slit can be erased at-a-distance by its entangled twin even after the annihilation of the photon itself. The choice was made between the joint detection of a single two-photon amplitude that involved either the upper slit or the lower slit (read which-path information) or the joint detection of a pair of indistinguishable two-photon amplitudes involving both slits (erase which-path information).
Unlike all previous experiments the present work takes advantage of two-photon imaging. A photon passes through a standard Young’s double-slit for its complementarity examination. The quantum correlation between this photon and its entangled twin allows the formation of a “ghost” image of the double-slit on the side of the entangled twin. Thus, the which path information is completely passed to the entangled twin photon and can be erased by the detection of the twin. After the detection of the photon which passed through the double-slit, a random choice is made on the Fourier transform plane of the “ghost” image between “reading complete information” or “reading partial information” of the double path.
The new approach shows clearly that any attempt to interpret the physics of the quantum eraser in terms of complementarity examination on a single photon leads to counterintuitive results and paradoxical conclusions ..."
The authors, Giuliano Scarcelli, Yu Zhou, and Yanhua Shih, go on in their paper to describe the Klyshko model as a potential theoretical explanation for the phenomena as follows:
"As we pointed out in the introduction, the interpretation of the quantum eraser results in terms of complementarity examination on a single photon is troubling. On the other hand, the straightforward calculation presented here can be intuitively captured if it is based on the concept of nonlocal two-photon amplitudes and their coherent superposition. In this sense, the physics behind entangled two-photon phenomena seems having no classical counterpart in electromagnetic theory. In order to help clarifying this physics, Klyshko proposed an “advanced-wave model” [20] that forces a classical counterpart of the concept of two-photon amplitudes and the associated two-photon optics. In his model, Klyshko considered the light to start from one of the detectors, propagate backwards in time until the two-photon source of SPDC and then forward in time towards the other detector. The two-photon source is thus playing the role of a mirror to keep the proper transverse momentum relation of the entangled photon pair.”
arXiv:quant-ph/0512207v1
Please take special note of the next to last sentence of the above quote, which
is from a peer reviewed journal. Does time reversal explain this experimental result?
In the now defunct chain titled “
Superluminal Communication” (see
https://www.physicsforums.com/showthread.php?t=250578), I had attempted to raise another paradox – one in which experimental results (which I still think was good science) seemed to challenge our common conceptions of special relativity. The common theme in that chain and in this chain is the possibility that through one universal concept, (e.g. time reversal) a “particular” paradox of quantum physics could potentially be understood.
Do you feel time-reversal theories might have explanatory value? If so, I would hope that this chain and the chain on Cramer’s theories (See
https://www.physicsforums.com/showthread.php?t=177506) might become more substantive in their content. As to the Cramer chain, may I proffer the apologetic update on John Cramer’s Transactional Interpretation of Quantum Mechanics (TIQM) that Dr. Ruth Kastner of the University of Maryland provides in her paper titled: “Cramer’s Transactional Interpretation and Causal Loop Problems” (See
http://arxiv.org/PS_cache/quant-ph/pdf/0408/0408109v1.pdf) (Yes, Dr. Kastner’s paper is not peer reviewed but, in my opinion, it should be considered)
[For those that are not familiar with Cramer’s work, it is built on Wheeler-Feynman emitter-absorber theory of radiation (see
http://en.wikipedia.org/wiki/Wheeler–Feynman_absorber_theory)
As to this chain, I would again like to proffer (as I had intended in the aborted “Superluminal Communication” chain) the TSQM model of Yakir Aharonov and Jeff Tollaksen for Forum consideration. (see New Insights on Time-Symmetry in Quantum Mechanics; Non-statistical Weak Measurements; Weak measurements, weak values, and entanglement; Pre-and post-selection, weak values and contextuality; and Robust Weak Measurements on Finite Samples). And, in order to comply with Forum Rules please consider also Jeff Tollaksen’s paper titled “Pre- and post-selection, weak values and Contextuality, 2007 J. Phys. A: Math. Theor. 40 9033-9066 doi: 10.1088/1751-8113/40/30/025 (see also: http://arxiv.org/PS_cache/quant-ph/p.../0602226v3.pdf for those of us who do not have free subscriptions to this journal)
Last, please consider M. S. Leifer and W. Spekkens paper titled "Pre- and Post-selection paradoxes and contextuality in quantum mechanics" [Physical Review Letters, 2005] in which they state: the "study of quantum systems that are both pre- and post-selected was initiated by Aharonov, Bergmann and Lebowitz (ABL) in 1964 and has led to the discovery of many counter-intuitive results, which we refer to as pre- and post-selection (PPS) effects [2], some of which have recently been confirmed experimentally [3]." ABL foundations the research that Aharonov and Tollaksen are currently conducting. As you will note from any review of the literature, the topic is not without some controversy. In fact, when Drs. Leifer and Spekkens go on to note that ABL’s experimental confirmations “have led to a long debate about the interpretation of the ABL probability rule [4]”, it is Dr. Ruth Kaster’s paper titled “The Nature of the Controversy over Time-Symmetric Quantum Counterfactuals” that they were citing [see R. E. Kastner, Phil. Sci. 70, 145 (2003)].
