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Hossenfelder's explanation seems correct to me (at least at the popular science level). I do not exactly understand what you mean by "the same sensor". If you intend to replace them by just one large detector that clicks if either D3 or D4 are hit, then this is not equivalent to which-slit...

That statement is a bit too brief and uses a rather limited definition of what interference actually means. You will indeed not get a spatial or temporal modulation pattern of the intensity (which is usually called interference pattern) for orthogonally polarized beams. Still, the...

That is, however, still wrong. You need to establish the physical meaning of your "ellipse". What does it mean physically that the difference from the center to the outline of the ellipse changes? It cannot be the detection probability. If the detection probability can take any value that is not...

This indeed is the best classical approximation there is, but it still does not match the experimental predictions. Below, I uploaded two figures from my quantum optics lecture which discuss exactly that question (sorry for the German). It considers an entangled photon pair of opposite...

I do not see how this is relevant for my remark. It was aimed especially at the term "pre-existing correlations" and your statement "They can't be pre-existing (if you preserve locality) unless you reject Bell." "Pre-existing something" is ill-defined. Pre-existing correlations are a clear-cut...

Can you provide a reference for this statement? This claim is contrary to pretty much every single reference in the field. Just to make the terminology clear: "pre-existing correlations" does not mean that the individual measurement results are pre-existing, but their correlations are. If you...

The factor of 1/2 is the quadrature variance of the vacuum state, so there is no possibility to avoid it. One can redefine the quadratures such that this variance becomes 1 or 0.25, but in any case this redefinition needs to be applied in both equations. Squeezing is always measured relative to...

For squeezed light, the spread of one of the quadratures Q is reduced, while the spread in the orthogonal quadrature P is enhanced. If one does the math, one finds that the quadrature variance along Q is ##(\Delta Q)^2=\frac{1}{2}e^{-2r}##, while the variance along P is ##(\Delta P)^2...

Sorry, I have been a bit busy myself. Actually, it is a mixture of all possible relative phases, but the geometry then "sorts" them such that the detection probabilities will resemble two out-of-phase patterns. Calling it collapse results in a preferred interpretation, which I usually try to...

I do not intend to enter into discussions of interpretations, but I would like to comment on the state of the community. I had the pleasure of cohosting Gregor Weihs last week in the colloquium of our department and besides funny/tragic stories about what discussions with Joy Christian are like...

Great. Thanks for letting me know. The issue remains the same: It is not meaningful to attribute the which-path bias to the photons. You need to attribute it to the detection positions. While the set of all photons has a 50/50 probability to go through either slit, the subset of photons that...

Just for the record. That very paper is considered to be questionable by a relevant part of the scientific community working on semconductor quantum optics. No other group has ever been able to reproduce the data on bulk GaAs in the 15 years after the publication and most people assume that the...

Just as a disclaimer: Talking about wave-functions for photons is difficult as they are relativistic particles without rest frame. For example you cannot really put them into eigenstates in the sense that you perform a measurement and if you perform it again and again you will always find it in...

This feature is present indeed already in classical physics. If you consider reasonably narrow slits, you can approximate them as point sources emitting the same amout of intensity. The intensity of a point source falls of with distance r from the slit as ##\frac{1}{r^2}##. If you place a...

Depends on what you call significant. There will be a tiny shift, but you will need to detect a very large number of photons to be able to identify it. Already classical optics predicts that there should be a shift. The lens in the signal path actually performs a Fourier transform, so all...

This is for exposure times of 2 milliseconds and high luminances on the order of more than 1000 cd/m^2. I am not sure that these conditions are really that comparable to the conditions you use. At high light levels it is easy to have a linear response. At low light levels, where all kinds of...

I can only second that. This setup is so macroscopic that QM will not add anything to understanding it. And: yes, it is expected that for such a setup the total intensity behind the double slit will be the sum of the intensities of the single slits. This is tested frequently in student labs all...

And how did you perform the background correction? Did you take a picture with all slits closed as the background and then subtracted this data from your other pictures pixel by pixel or did you subtract some flat background?

Nobody doubted that. The point is that we have Malus's law, so that the transmission probability depends nonlinearly on the relative angle between the polarizer and the light field. The scenario considered by Claude Bile is that you have light oriented along a certain polarization (say...

They claim to use laser-induced fluorescence detection in the first paragraph and then state that they can do so at near the natural linewidth limit of 30 MHz. This is the resolution of the laser-induced fluorescence detection and should therefore be the linewidth of the laser. It is not related...

Well, yes, that is the standard problem in the field. Of course they do not really set ##\hbar=1/2##, but the question is what people prefer the quadratures to behave like. Some people want them to behave exactly like position and momentum, while others want them to correspond to the fields...

It is a bit difficult to suggest a better introduction without knowing about your background. This review article from the Review of Modern Physics provides a reasonably pedagogical introduction: https://arxiv.org/pdf/quant-ph/0410100.pdf The introduction to what continuous variable...

To some degree: yes. There are solid state lasers such as Nd:YAG, where that is certainly the case. Some semiconductor diode lasers, especially the ones which are widely tunable, instead work on the principle that the material is simply flooded with electrons and holes and lasing occurs from...

I fully agree that you need QM to explain atoms. You just do not necessarily need atoms to build a laser. Free electron lasers or many semiconductor diode lasers work quite differently. I also agree that "classical" and "non-classical" are technical terms in quantum optics. Nowadays...

The definition of "what is non-classical" is a nontrivial one, but the standard definition in the discrete variable quantum optics community is that intensity fluctuations below shot noise make light fields non-classical which is technically described by the equal-time second-order photon...

The double slit is a momentum measurement. You get a different result for each different value of particle momentum in the plane of the slits. Or putting it more simply: A light field arriving at an angle will show a shifted interference pattern compared to a light field arriving at normal...

Indeed. I must admit that an Aspect ratio of 1:3 sounds a bit unusual to me, but I like it.

What you have in mind seems to be a simplified version of electromagnetically induced transparency, where you simply remove one of the two beams and do not really have a dark state. It might help to have a look at an introduction on EIT. If I get your system right, you essentially consider a...

What kind of fiber are you using and how long is it? Is it single-mode or multi-mode? What is the sensitivity of the detector? Cladding modes exist (see, e.g., here )and their properties depend among other factors on the refractive indices of the cladding and the overcoat. These are typically...

I cannot follow. Maybe that is a question of terminology? Nonlocal correlations are pretty exactly the thing @vanhees71 proposes. Every serious full quantum field theory has these built in automatically. Mermin once wrote the hilarious tongue-in-cheek quote: "My complete answer to the late 19th...

No, it does not show that. The authors actually set out to show quite the opposite. The central parts can be found right in the introduction. The authors state "According to quantum theory, quantum correlations violating Bell inequalities merely happen, somehow from outside space-time, in the...

There is no paradox here. Stinespring's dilation theorem tells us that we can always go to the "church of the larger Hilbert space" as Smolin called it. Any non-unitary channel (e.g. a von-Neumann measurement) can always be considered as a unitary map in a larger Hilbert space (e.g. including...

What is your integration range? If you allow the range outside of the range between 0 and 2 pi, the states will not be orthogonal. If you limit the range to the range between 0 and 2 pi, you will get a photon number spectrum that must necessarily extend towards minus infinity which is obviously...

Let me emphasize it again: This includes a setup where you compare scenarios where the total power arriving at the setup is different. You compare the field squared to twice the field squared which yields the factor of 4. You have twice the total intensity making it through the slits in the...

Yes, I fully agree with that. I just think that we are talking about fundamentally different topics within different physics courses. I would introduce the physics of going from 1 slit to n slits in a course on classical optics or maybe in a course on spectroscopy, while the "double slit vs...

Well, it is misleading. You get a factor of two from interference and you get another factor of two from doubling the incoming intensity. Actually, I have never seen the "factor of 4 thing" being taught to students because it obscures things. The reasonable comparison is to illuminate the left...

You cannot distinguish these situations. Two perfectly phase locked LOs with an identical spectrum are effectively a single light source. And: yes, single photons are never sinusoidal in practice. They do not have to. All you need to do to have a Fock state is to have a photon number of 1 in...

The problem is that this distinction is not tenable. Higher-order interference is not necessarily non-classical. The HBT-effect is a good example for that. Considering single photons you need Ugo Fanos explanation that utilizes Bose statistics. However, for a classical thermal light field you...

No, that is not correct. You always need to compare the same total intensity arriving. Typically, you also do not compare a double slit to an individual slit, but a double slit to the sum of intensity patterns of two individual slits, where each slit gets the same intensity as one of the double...

You just compare to the wrong results. In the double slit you need to get 4 times the intensity of a comparable result with no interference happening, which would be: $$|\tilde \psi(p)|^2 + |\tilde \phi(p)|^2=\frac{1}{\pi}$$ So you would expect 4 times this value for the peak intensity in the...

I do not get what you mean. In case 1, the observed intensity will be 16 A^2. The peak intensity in a double slit for constructive interference is 4 times the peak intensity that you observe when only one slit is open. For example for the first slit, the field present is \psi_1+\Phi_1, so the...

Indeed. However, if one reads Glauber's article, it is exactly this full statement which he focuses on. When Hanbury Brown and Twiss performed their famous experiment which is considered as the birth of quantum optics by some, it was met with heavy criticism because many people thought that the...

Allow me to cite Nobel prize winner Roy Glauber (The whole article I quote from can be found here: https://arxiv.org/abs/nucl-th/0604021 ): "When you read the first chapter of Dirac’s famous textbook in quantum mechanics [8], however, you are confronted with a very clear statement that rings in...

I would argue that if you accept that the quantum state is a fundamental description of what is going on, then the question is settled. Classically, it is clear what you need to have radiation: the simple "accelerated charges radiate" is something everybody has heard of. In QM things are of...

Why? You get the probability amplitudes for the system being in the excited/ground state for each and every delay tau after the excitation process. In principle one can get also the off-diagonal elements (typically called coherences within the optics-related communities). Which deeper...

I am a bit puzzled here because - in the ensemble average over many realizations - this is a standard experiment that is performed in a huge number of labs in chemistry and physics routinely. Leaving aside the simplest versions using time-correlated single photon counting, this is for example...

About 15 years later the same group even went up to 2000 atoms and masses of 25 kDa. However, they needed to use a different kind of interferometer to show interference. Original publication (behind paywall) As has been pointed out before, there is nothing mysterious about the size of...

The detectors used for homodyne detection are usually far from being single-photon sensitive. Accordingly, you measure two photocurrents, not individual clicks. These are of course proportional to the photon number present in either detection arm. However, for pulsed operation typical local...

Sorry, for being unclear. I was interpreting the initial remark about spectral lines to imply atomic transitions that change the principal quantum number. For magnetic dipole transitions, these are forbidden in the non-relativistic case, but become weakly allowed due to relativistic effects...

Bransden and Joachain discuss this in quite some detail in their book on the physics of atoms and molecules. However, I would like to point out one thing that people often are not aware of: You cannot simply flip a spin using photon absorption. In dipole approximation (and also beyond) the...