Non-Particle Duality — Brigitte Falkenburg

0:00 ...photon is, but you know the atom has passed either here or there, and then the interference pattern has to be destroyed. This was a thought experiment, and then there was a series of developments in quantum optics to realize the experiment of this type, and it was harder than physicists thought. So, the principle of these experiments is how to achieve which wave information. First, a wave function of the atom or photon or electron beam. Then, this wave function or beam is sent to another state or a mass event of a meter. then one has a quantum state which is a superposition of both the positive parts and interference should happen. Then the path is marked by means of a sudden device that produces an element with auto-alert internal states. For example, the excited internal states of the atom in the front experiment of Kali collaborators. And then, due to orthogonality, you have the functions, the interference terms are cancelled and the interference is superior, but it's all in the wave feature. One of the first very nice experiments performed in this wave was made by Dürer and Prennberg. That's a now unique group at that time . They prepare the wave function of an atom, so a matter wave, and send it to an interferometer of two standing light waves. It's a very nice example of wave-particularity because you make matter interfere by something like a light double slit. And then you have a black reflection. One part of the beam passes through, the other is a black wave reflected, and then you get to interference pattern. This was observed. applied in order to adequate atomic states and make the interferences appear by means

2:30 of entanglement with autogonal states and really here in this diagram you see the interferences in the far field, so how does the experiment work? So, you'll make this interference and then you'll somewhere in the far field you'll make the observation by shifting a detector through and then counting how many atoms arrive at the detector at which position and the solution along the detector is this interference pattern. And here, the same, what we see is termed in marked states, the disappearance is disappeared. But one may add a device for preparation and measurement of a superposition of these orthogonal states, so add a third device, and then the interference reappeared. So, you may switch arbitrarily between this and that coloration long before you finally go to your particle detection at the screen. Then there was a famous speaker of Wolborn, collaborators on quantum erasure. They used a double slit to pass the colorisators. Here is the double slit, there is a diagonal polarizer, and there in the other dimension. And so when the light passes through the double slit, the light which passes through the left slit, is left diagonal polarized, and to the right slit is diagonal polarized to the right, and the difference disappeared. It was not observed. And on the other hand, if you put in a horizontal polarizer, the vertical contact lens are cut off and only this remains and in this way, the path marking is erased and then interference disappeared. The nice thing in the experimental device was that they used an EPR-like experimental device.

5:00 they have a non-linear down converter that puts one photon in a pair of two photons of lower frequency or energy but they are EPR correlated and then it's efficient to put in and flip around the polarizer the other branch of the experiment with a space-like distance between both and then you have a coincidence counter, then you may do your recording and you may look at your data five years afterwards, wherever you look at the front and you just have to store all the information of how the polarizer here was placed when you have a coincidental rate. And then you see in the panels of the position, of the orientation of the polarizer, You either get known interference, the path is marked, or you get interference, the path marking is raised. So I cannot go into further details for time reasons. I just want to mention it, regarding this experiment, there are no causal mysteries at all. if you are consequently thinking about preparing waves and detecting particles. But once you try to get through it with a classical or quasi-classical particle concept, then you get into real troubles. So I would suggest not to do that, but to look deeper into physical practice. So what does it mean, these results of physical practice So what is there, I want to draw some ontological conclusions and we'll see how far we may get to it with that. If we take this attitude of preparing race and detecting particles with particles seriously, and I suggest that we should take it very seriously, then we have to assume that random ways that are somehow real in the sense that they have causal relevance

7:30 for experimental outcomes, they propagate through a classical world, through a macroscopic environment through a macroscopic experimental device in a macroscopic laboratory. After decoherence, here I put in this term, I did not yet mention the decoherence approach, but in order to explain what happens, I think it's very important to take into account. After decoherence, physicists detect particles. According to Hacking's criteria from his famous book representing it in the meaning, if you can spray them, they are real. According to Hacking's criteria, the waves are real because they are prepared in order to generate some kind of preparation. And I think this should also be very serious here. It's completely in the spirit of Hacking's discussion because Hacking applied this criteria to electrons but as if electrons were real particles. But they are not. the electron beam that makes the example in his book in a particle experiment in an experiment of particle physics the electrons coming from the beam from the accelerator are classical beam as you may see for example that synchrotron radiation of course they behave according to the laws of classical electrodynamics but once they get into the action zone or into the detector they do no longer behave classical but as quantum objects and then you should describe them as quantum waves and take them as quantum waves propagates to a classical world. So, Hacking did not take into account that problem. But if you apply Hacking's criterion to the propagation of quantum waves with a certain preparation that may be changed in one way or in the other way by adding additional experimental devices. If you take it seriously, you have to accept that wave particle is a duality,

10:00 it's a feature of nature. And it should also be, one should also take into account that nature, not only physicists in the labs, but also nature, prepares many super-squantum waves from a real point of view. of, for example, neutrino oscillation. The neutrinos are not generated in the physicist's laboratories, but they come from the sun. And there was the famous solar neutrino puzzle that was finally dissolved on the basis of the super-community experiment. And it turned out that neutrinos oscillate. They are in a quantum state that is a superposition of two kinds of neutriners and in the moment the neutriners are detected, the rate is smaller due to oscillations than if there was no superposition of two kinds of neutriners. On the other hand, there are the KLD case that violate CP violations. The KLDs come in a superposition of two states of opposite parities and this is the key violation and then they decay into different collections of pions, but there's also so-called quark mixing this means in the standard model of current particle physics, the electroweak theory or the Salon-Weinberg theory the Lagrangian of this theory is quite complicated and it contains a matrix, the so-called Kobayashi And this matrix expresses the quark mixing, and the problem is, the matrix expresses the matter of fact that the mass eigenstates of the quarks are not identical with the flavor eigenstates of the quarks. And this quark mixing is within the nucleus, and if you are a realist, they are within the stable. Okay, and then last five minutes I'll come through. I want to explain a simple polarizer experiment, which is much simpler than the sophisticated experiment of recent quantum optics, but it shows what happens when you prepare the sensitive particles. We have a

12:30 laser, a low-intensity beam, a vertical polarizer and a horizontal polarizer, and after both polarizers, you have a vanquium state and no light comes through. Cross polarizers don't let any light pass through, they prepare the vanquium state. But if a third polarizer is put in a diagonal polarizer, then a polarizer is shifted. After each polarizer, the amplitude of the laser beam or photo beam is decreased from one to one point or something like that, and what is observed are fluctuating particle detections. So each polarizer prepares states of lower amplitude, but finally some light gets through and fluctuating particle detections are observed. So in a particle picture, the polarizers work as absorbers. If a proton does not come through due to wrong a polarization, it remains absorbed by the polarizer, it's an absorber. And the second polarizer is also an absorber, and you have two absorbers and no photon pass. In the particle picture, you are agnostic, or you will defend an ignorant interpretation of whether after the first polarizer there is still a photon or not, but finally no photon remains. They are swallowed either by the first or the second. But if you put in a third absorber, a third polarizer, then some photons pass again. So you have two absorbers and no photon passes and three absorbers let some photons pass. So in the particle picture you have really a puzzle, how does the third absorber generate the photons that come finally through? On the other hand, is a wave picture, simply classical light behavior until here when you get a single particle or photon detections, but simply a classical light behavior, you may perform this experiment with a classical white light and you can see the light spot, this is polarizing. Quite trivial and well-known experiment.

15:00 So in the particle picture, you are not and the wave picture you are able to explain what happens finally at the photon counter. But in quantum field theory you have a complete explanation. Each of the polarizers prepares field nodes of unsharp occupation number. If you here have a laser beam, which is more or less occupation number one, one photon per time interval in the whole experiment. Then afterwards, in the polarization presentation of polarizer defined basis, the amplitude is decreased and polarization is shifted by each of the polarizers. But in the occupation number representation, after each polarizer you have a superposition of one photo state plus the vacuum state and so this superposition survives and in this way the fluctuating particle detections are explained so finally I would like to have two or three more minutes to explain the possibilities of interpreting that in a realistic part of this If you want to defend real particles, you end up with the absorber paradox. The third absorber seems to generate photons with real waves. You have a field strength pattern from the point of view of quantum field theory because if the polarization state is sharp, you don't have a sharp, well-defined application number of field amplitude and vice versa. They are complementary in more sense. or there are some generalized Heisenberg relations for phase and occupation number. And I really have my doubts whether it's possible to defend the ignorance interpretation of quantum field theory. I have my doubts. If someone comes in to explain me, I'm curious about it, but I have my doubts. On the other hand, with an instrumentalistic view of the quantum field modes,

17:30 The whole experiment, well, preparation determines conditional probabilities. The probability after getting a photon, given that the polarizer or the collection of polarizers before were in that orientation. The polarizers change the conditional probabilities in a manner and a certain way. that the causal relevance of preparation for the experimental outcome is in perfect agreement with the regularity view of causality. But only the final photon detections are real from an instrumentalistic or an empiricist point of view. And then I would like to ask whether preparation results are less real than the detection, I have my doubts, but also from the other experiments I discussed before, the which way experiments show that storage of information is sufficient. You do not have to look whether the information about the past market has to be read out or not, and this is a clear hint for me that instrumentalism cannot be defended. it. And so, to the instrumentalist, one might also ask, with regards to the panorizer experiment, on what do the panorizers act? If not on the field state, does a miracle occur? Or should we simply be agnostic about that? And finally, I would like to suggest a Kant's view. What What is still valid from Kant's theory of nature is a constitutive principle of substance. Substance as a conserved property. A particle is a collection of conserved magnitudes and a photon, in the case of our polarizer experiment, is a collection of energy and spin. And then there is a regulated idea of something is propagating. The polarizers act on a wave like a beam that is unobsorbed on its own in principle, like a Kantian glumenon simulates out. And then one might conceive of the quantum waves or field modes as if they were real objects. The physicists in their labs, when they prepare a quantum state, a change of progression, they deal with them as if they were real objects. And this is the view of quantum physics that was suggested by my former Ph.D. student Ernan Brindler,

20:00 that the quantum field modes of quantum wave function unify the photomounts under human experimental conditions and that this should be interpreted in a sense of Kant's concept of teleological structures. slide I made tonight after discussions with Paul Taylor but also reading a paper on decoherence is decoherence a way out of all these troubles about objective reality decoherence would suggest relational ontology the quantum field decoheres due to a microscopic environment as I read the cosmic microwave background the laboratory, but contains many more particles in the air as well, but then I would think that the problem is shifted to another content topic, namely what he would co-hears the environment, the country and totality problem that leads into all the puzzles of the way function of the universe finally. However, that's a point I got from the discussion with you Paul, I I think that we have no real physics, no physics that describes real physical reality from two strong idealizations. And we should be aware from all the work that exists on decoherence, that quantum mechanics and quantum utility are highly idealized theories. The environment acts substantially on quantum mistakes, giving rise to decoherence. and perhaps this might help with the quantum mechanical wave function interpretation project. So thank you to the patients. We started five minutes late, so we have time for about ten minutes of questions. Chris? I've had a number of comments, but maybe just a bit to you. On this last slide, the problem of what decoheres the environment. That seems a genuine question if you're doing an environmental decoherence program, but there are other decoherence programs. cross-graining, cross-grained degrees of freedom end up being deep in here while they're microscopic degrees of freedom, and that's the kind of thing that Gell-Mann and Harper-Mann's guys do. So you can perfectly, consistently talk about deep coherence of the universe, deep infrastructures in the universe as a whole as a closed system, and how it could give you a particular position of quasi-classical history.

22:30 And the other... I don't believe in the consistent history explanation, but that's another... Go ahead. And the second point was, to what extent did you think the claim about preparation and detection being asymmetric procedures is a universal claim? Because I can think of some experiments where that claim, I mean a non-particle-physical experiment, but I can think of some experiments where that claim is false. Sure, sure. I did not want to make a universal claim, but I just wanted to say in most cases it is like this. But for example, it was very hard to prepare a single photon state. this was only done in the late 80s in the group of Branger that you generate a single photon state, a particle-like photon state, so to speak, with occupation number exactly one by a tangled photon pair, a photon pair, where one of the two branches, in one of the two branches the photon is absorbed, then you know in the other branch it must be an occupation number one state. but it's not just to draw your attention to a quite important topic that is neglected in the discussion. Let me see if I've got the big picture so what what I think you've done is to extract this Kantian view out of out of Copenhagen plus the pragmatic attitude and it's been this very nice kind of transition one of the nicest I've seen from Copenhagen to Cannes yes so I think that works very well so but there was one slide that puzzled me but then I was thinking about the big picture and maybe can understand it in the way it was the slide that had the on what there is, the first slide on what there is, and yes, when you say that a wave particle duality is a feature of nature, well that really struck me, and that sounds like very much of a, some sort of more realistic kind of assertion, but then I was thinking, well you're using nature here in the Kantian sense as the sense of the world of our experience of phenomena. I don't think anybody is going to think. Am I right about that? I'm struggling with myself for, I don't know, more than 15 years now. I'm half of a Kantian and half of a realist.

25:00 So you're in a superposition. It's really a problem. And the suggestion to perhaps resolve the problems with realism in terms of well let me let me just post it if I can just post to you the problem that the realist might raise to this kind of statement which is that well look at you know fundamental energy levels you know you're not going to you're not going to find wave particle realities you're not even going to have you're going to have some other very weird kind of structure but wave particle reality presumably is going to be derivable from you know, the Planck scales and stuff? Well, at this point, I'm a conscientious because Planck scale is an observable principle, at least for the moment. Okay. Most probably there are, at least at most, quite indirect tests of that. And I do not know whether it's justified to extend the scales down to the Planck scale because the scales are basically classical on the basis of basic use of Bohr's good old correspondence principle. Where do we know that down to the Planck scale there's something like a classical length, a classical mass, a classical time? Where do we know that? We just assume that because the construction of the scale works very well coherently over all the scales of the universe that are accessible to us right now. but the Planck's cane is as far away from the quarks as the quarks are far away from us. It should be kept in mind. I think the general explanation is that this motion will break down. The general explanation is that the flame breaks down as a Planck's cane. But I ask, why are we sure that before, in the region between quartz and Planck's cane, does not happen anything strange? We have a couple more questions. Oliver. Well, I'm going to be very correct to say, but first you come up with a question, it's just not fair to love Everett in the other realist interpretations. I simply did not understand. Ganz unfair, ganz unfair.

27:30 I did not get it acoustically, could you speak louder again? Sorry. it's not fair to knock Everett in with the other realist interpretations because you accuse them of being ad hoc having ad hoc features and being incompatible with relativity and Everett is excellent on both those fronts so that was just a quick ride so the main question is you say you have no causal mistress if you stick to this detect particles, compare waves in the picture. But if you try and impose a realist particle picture, you get causal missiles. But what about the transition from the wave to the particle detection? What about the time these two things together? This mystery remains, yes. The picture is absolutely nice at the probabilistic level. At the probabilistic level, it's no problem to unify classical physics and quantum physics but at the level of the individual events it's impossible. I simply suggest to accept that nature is like that. Nature also is like that in the real structure of the standard model of particle physics and asymmetry of matter and anti-matter. We all have to accept that. Well, but I would not like to suggest stop further research on the quantum measurement problem. That's another story. Well, if nature is in a superposition of Kantian reality and real reality, I could explain it. Michel? I would like to ask you a question about the opportunity or rather the necessity of positive idea that there is a preparation of waves. Because you know that there was a model built by Landet after the idea of Duet, that you can explain very excellently the interference pattern by the positive only, that particles have quantized interaction with the mass of the screen, out of which the two holes are in.

30:00 So that means that somehow you can explain as well this interference pattern by a particle picture or by a wave picture. So there is a deep under-delimination apparently. Of course the wave- That's why I suggested to think about the polarizers experiment. Jeff? Are we in first? Maybe. Somebody ask a question. I'm sorry, but I have a question about because I would like to know as you interpret this because it seems to me that in the next book Yes, because in the book it seems to me that he uses this criterion in the controversy between scientific realism and instrumentalism about the existence of the unobservable aliens and the things that it works. But in the general view of the book, it is also against the internalist realist. So it seems to me that it gives to this criterion a more general import on the general question of realism and again anti-realism. So, I would like to know, what is your position about this? I always read Hacking's argument as the hammer and nail argument, to put the nail into the wall, you need a hammer. And the only thing I've addressed here is that the hammer is not a particle field, but a wave. It's a wave, it's a disunderstood. Yes, and about the other question against which kind of realism, or anti-realism, against which kind of anti-realism this argument is, I did not really analyze that question.

32:30 One last question, quick and quick answer. Okay, this is really a small pointer. It's about your final polarizing experiment. that you have that excludes particles. Because imagine the particles are like people, and they all come with passports there. And polarizers like border crossings. So if they come with a banned passport, then they get killed. Otherwise, if they come with a different passport, their passports are confiscated, and they get a passport of that country. So now if they go from there to a banned country, they'll all be annihilated. But if they go from there to a different country, which is not banned, and then the hospital's confiscated or new hospitals, and then they can go to the bad country and get through. I mean, so if, basically I'm saying, if polarizer changes some property of the particle as it goes through, then there's no problem explaining just that sequence of three exorters in terms of particle. I mean, it seems to us like you've got the two nothing is true, you put something in the middle, something is true, but if the polarizers are changing the particles, and you measure it's a split of them, but they must do something wrong, and they're changing, then you want to, nothing is true, the cross polarizers. Yeah, but they can change them like the cross-polarizers, and they get the cross-polarizers change. It's a nice logic, I have to think about it. Because I, this is where you can actually, I do this with, when I teach a cross-polarizer, You have three pieces of polarizer, and you hold them up, and you cross two, and that they get through from the middle of something. You've got the same particles, but you just add the fact that it really gives us lasers and so on. So, you know, you ask the students, how would you? Could you explain to some particles that somebody usually suggests what changes them? The problem is also that the textbooks on quantum field theory or quantum optics are not really explicit on what is a polarization state and what kind of property of a photon is this. It's really hard to find something in the literature. And once I sent an email to Stefan Do, from one of the UNI group of these experiments, it simply did not

35:00 send me an answer to this. It's really a trivia question. Well, thank you very much, Brigitte. Thank you.