I also wanted to comment that your description about how entanglement versus simple superposition in this case is what kills interferences, was really well done and well explained.

10:09 "that shows that is not us observing the path of the photon that destroys the interference, it's us introducing anything that becomes entangled with the photon " THANK YOU!!. Jesus, I can't count how many times people got it wrong saying that is a the passive observation that causes the "collpase". Even some physics and science content creators got it wrong sometimes.

@maria_violaris

6 ай бұрын

Yes! This point is very obscured in the mainstream narrative around the double-slit experiment. I've had multiple conversations even with quantum researchers, where they never realised that a single particle could be the so-called "observer" that causes the photon in the double-slit experiment to decohere (even though they understood the physics well, and immediately agreed once I put it this way).

To see map this quantum mechanics physical experiment onto a simple quantum computer circuit is enlightening.

Your explanation of the mystery of single-particle interference using quantum information theory is great and I will use it the next time I teach quantum mechanics. While you didn’t offer a solution to the mystery, quantum information theory does provide one. In simple terms, the mystery of wave-particle duality in the double-slit experiment is that you get point-like (particle) outcomes that collectively reproduce an interference (wave) pattern. Feynman said this mystery “is absolutely impossible to explain in any classical way” and “has in it the heart of quantum mechanics. In reality, it contains the only mystery” (Chap 37 of The Feynman Lectures on Physics Volume 1). This really reduces to the mystery of quantum superposition of course. If you try to solve this mystery constructively, i.e., via causal mechanisms, you end up without a consensus solution. For example, in Matthew Geleta’s KZread video “Tim Maudlin: Philosophy of science and quantum physics,” Maudlin says that to solve this mystery one needs to say whether there is a particle being guided by a wave (like Bohmian mechanics) or a wave that collapses to a point-like outcome (like spontaneous collapse models) or a wave that never collapses but instantiates all possible point-like outcomes (like Many Worlds). None of these constructive alternatives to quantum mechanics has consensus support because they violate locality or the uniqueness of experimental outcomes. Quantum information theorists avoid these controversial options altogether because they abandoned “constructive efforts” and instead rendered quantum mechanics a principle theory a la special relativity. That is, they derived the formalism of quantum mechanics from the empirically discovered fact called Information Invariance & Continuity just like the formalism of special relativity is derived from the empirically discovered fact called the light postulate. The reason special relativity is universally accepted even though it doesn’t provide a causal mechanism for length contraction or time dilation is that the light postulate is justified by the (compelling) relativity principle. Information Invariance & Continuity is the information-theoretic counterpart to superposition and, as we show in our book "Einstein's Entanglement: Bell Inequalities, Relativity, and the Qubit" (due out in June 2024 with Oxford UP), Information Invariance & Continuity can also be justified by the relativity principle. So, quantum information theorists have shown that the mystery of wave-particle duality in quantum mechanics is a necessary consequence of the relativity principle just like the mysteries of length contraction and time dilation in special relativity.

Thanks , you're always providing amazing content!

I am already following you on Google scholar so I will be eagerly waiting for your further articles and newsletters and papers

Cool video! I actually started a series of videos on this same subject a few weeks ago and will be doing a few on the delayed-choice quantum eraser as well!! 🙂

@maria_violaris

6 ай бұрын

Hi Diego, thanks and your videos look awesome! Great to see more content on using Qiskit / quantum computers to explain these experiments. It's very nice how you introduce the phase gate to simulate photons hitting the screen, and that you can see the different distributions with the real quantum computer. Also cool how your videos go through each stage of the "thought experiment --> quantum computer demo" process. Looking forward to your eraser videos too! 😊

@diemilio

6 ай бұрын

Thank you so much,@@maria_violaris. I really appreciate your comments 🙂

Very nice and interesting video!!! I have a question for Maria: is it possible to simulate time travel with quantum circuits? I mean: if you change the state of the qubit in the past then you misure a different outcome in the present?

@maria_violaris

6 ай бұрын

Thanks! I have a video simulating time-loops ("closed-timelike-curves") with quantum circuits coming soon, it will be released in around 3 weeks. These time-loops may or may not actually be possible in our universe. To make sure that the time-loops don't result in paradoxes such as the grandfather paradox, we end up having to impose a constraint that means you can't change the state of a qubit in the past to change its state in the present. But despite resolving grandfather paradoxes, the constraint leads to lots of weird things happening, such as loads of computational power. Lots more exploration of these ideas in the upcoming video!

@lucadepaoli4790

6 ай бұрын

@@maria_violaris Thank you for your answer and for your super interesting video that is coming about time-loops!!!! Can't wait! With quantum circuits everything is very AMAZING!!!🤩🤩

Just an FYI for the observed photon case of the two-slit experiment. Because light from a point source spreads out after passing through a single slit, you will not see two bright regions with dark in between as you drew when they are observed at the slits, instead you will see the broad single slit diffraction pattern from each slit, which are difficult to tell apart from each other.

@maria_violaris

6 ай бұрын

Hi, we do see two bright regions with dark in between, and in an experiment set up well they will be easily distinguishable, even accounting for the single-slit diffraction. For the case with a detector, the photon behaves exactly as though it went through just one of the two slits, so from each slit there will be a single-slit diffraction pattern. This has an intense central bright region, and then a series of much less intense bright regions (with dark regions in between). The resulting pattern on the screen will therefore be a combination of these two single-slit diffraction patterns of photons passing through each of the two slits individually. There will be two intense bright regions, centred at each slit, and then some much less intense bright regions either side. The two intense bright regions will be clearly distinguishable when the experiment is done well (i.e. adjusting properties such as slit-width, distance from slit to screen, photon wavelength appropriately). Then the intensity pattern will look like the one I drew on the screen, to good approximation.

I can't wait for the delayed choice quantum eraser to get published !

@maria_violaris

6 ай бұрын

Great, check back next Wednesday...! 😄

Why isn't the photon a physical wave instead of a probability curve?

@maria_violaris

6 ай бұрын

The interference in this experiment is due to the photon's quantum wave-function. This is very different to classical waves such as sound waves, water waves and classical electromagnetic waves, because it does not directly correspond to some energy and momentum propagating through space. To really understand the physical nature of a photon, we need "quantum field theory" (QFT), which shows us that "particles" are all stable configurations (excitations) of an underlying quantum field - a photon is an excitation of the quantum electromagnetic field. In certain macroscopic limits, this underlying quantum wave reproduces the classical electromagnetic wave used to describe light before quantum physics was discovered. Hope that helps, thanks for the question :)

@maria_violaris

6 ай бұрын

For more about how quantum field theory helps us explain the physical nature of underlying reality and wave-particle duality, I recommend Vlatko Vedral's blog post and paper entitled "The Everything-is-a-Quantum-Wave Interpretation of Quantum Physics", both are accessible online.

what the hell is a "pheyton"

Is she saying photon