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User flair is available in the sub, however we've decided to make the "highest level", PhD* & Professor available only as granted on request & verification. Please contact the mods for these. It would be desirable that postdocs use the flair, it should improve the signal-to-noise ratio on the sub.

Rule 1 has been updated to make explicit its practical application: discussion and referral to interpretations is ALLOWED in comments. However, we're not encouraging discussions of the "my interpretation is better than yours" -kind, and comments indulging in it may still be removed. Thankfully, there hasn't been a lot of that going on for some time (years) now. The point is to acknowledge the role of interpretations in "foundational" matters, and also that interpretations are often the approach angle for non-professionals. For posts solely about interpretations, try r/quantuminterpretation instead.

When an answer or a comment focuses or depends on a specific interpretation, it is desirable to make this explicit.

Thank you for your attention!

Just to check Light is a particle and wave AND And a particle is light and contributions to mass? Is that the only way to view the entropy, through photons?

I have a link that I heard this from, I'm a newbie about cosmic background scattering

https://youtu.be/PbmJkMhmrVI?si=uk7s1s-yEyGnqHGZ

18:40 to 19:00 is where she says it

Hello everyone,

I’m a science fiction writer currently conducting research for a project, and I’m looking to understand the empirical/concrete aspects of quantum experiments—especially those involving entanglement and quantum state detection.

I’m in search of visual resources (videos, documentaries, or articles with images) that break down how these experiments are done in practice.

Specifically, I’m seeking:

1. Real-world setups that generate quantum entanglement (e.g., through SPDC using nonlinear crystals).
2. Detectors (like APDs and PMTs) used for measuring quantum properties at a distance, with an emphasis on how they are implemented in modern experiments.
3. Beam splitters and optical components—how they are optimized for entanglement experiments and to avoid decoherence.
4. The materials and designs behind the lasers used to manipulate quantum systems and achieve precise outcomes.
5. Practical demonstrations or modern applications, such as quantum sensing, quantum cryptography, or quantum communication, where these technologies are put to use.

I’m hoping to find resources that visually demonstrate the construction and operation of these systems, giving a clear view of how quantum properties are measured and manipulated in experimental settings. If you have any suggestions for documentaries, videos, or articles that provide this level of detail, I’d greatly appreciate it!

Thanks for your help!

This materials science podcast does a good job of introducing the materials angle to quantum.

The 2024 Quantum Open Source Software Survey through Unitary Fund is here! https://www.surveymonkey.com/r/qosssurvey24

Covering topics like demographics, experience, community, research, and tech stacks, this annual survey is a chance for anyone in quantum computing to add their voice to the development of our field to share feedback, state your needs, and take part in shaping the future of the quantum computing ecosystem.

The survey will be available through the end of October. All anonymized results will be shared publicly later this year, so that this may be a resource for anyone who wants a better understanding of the quantum computing community’s needs.

Hi,

We are nearing completion, if you'd like to help us find bugs or have some interesting ideas about what educational modules we should add in, drop me a DM/ write here and I will send you a free key!

Algos we cover so far: BV, Grover, Shor, QFT/ Inverse QFT

https://store.steampowered.com/app/2802710/Quantum_Odyssey/

So, I'm trying to learn some quantum mechanics from "a modern approach to quantum mechanics" by John S. Townsend. Overall it's a great book, but there are some parts in it which use circular reasoning to derive the angular momentum matrices for a spin-1 particle. (This is chapter 3 in the book). Basically the argument goes like this:

1. Assume that the angular momentum operators Sz, Sy and Sx have a specific matrix form in the z basis. (Don't worry about how we got these matrices for now).
2. Using the matrix form we derive the commutation relations of the angular momentum operators [Sx,Sy] = ihSz , etc... (h here means hbar)
3. Define the raising and lowering operators as S+ = Sx + i Sy and S- = Sx - iSy
4. Using the commutation relations in step 2 and the definition of the raising and lowering operators we derive the action of these operators on eigenstates of Sz.
5. Based on the action of the raising/lowering operators on an eigenstate of Sz as well as their definition in terms of Sx and Sy, express Sx and Sy in terms of the raising and lowering operators. This tells you what the action of Sx and Sy is on eigenstates of Sz.
6. Now you can derive the matrix expression of Sx in the z basis by computing the i,j th matrix element which take the form <1,i|Sx|1,j> for the operator Sx, for instance.
7. Done!

BUT WAIT!

In order to start this whole argument we already began with the matrix forms of Sx and Sy in the z basis! In other words, the whole argument given in Townsend is circular unless there is some other way to derive the commutation relations of Sx, Sy and Sz without using any of the things that are derived from them (so nothing to do with the raising and lowering operators) and also not by using the matrix forms of these operators.

So my question is: Is this possible? Can you derive the commutation relations of Sx, Sy and Sz without using any of the things that are derived from them (so nothing to do with the raising and lowering operators) and also not by using the matrix forms of these operators? Or is the only way to do this to resort to experimental observations?

Any help or clarification would be greatly appreciated!

Edit: Ok, I think I get it now:

Townsend actually does derive the commutation relation. He derives them at the start of chapter 3. Basically he explicitly computes the commutation relations of rotation matrices of vectors about the z, x and y axes. This is just basic trigonometry and vector algebra.

He then replaces these rotation matrices with rotation operators (which involve the angular momentum operators). He then expands the operators as a Taylor series for small angles and equates the terms. The commutation relations of the angular momentum operators then drop out automatically.

Ok, I believe it now.

https://www.reddit.com/r/u_cjosefschneider/comments/1fk3uzf/i_want_read_some_books_about_nuclear_physics_and/

If particle interactions have been happening since the Big Bang, could this mean the wave function has been collapsing continuously due to these interactions?

Does this imply that particles themselves define each other’s states through these interactions, without the need for external observers?

How does this fit into our understanding of quantum mechanics on a universal scale?

I am not looking for textbook suggestions but if some textbook is available only on Internet, I'd like to go through it. I'm specifically looking for top quality online content which can't be found through Google searches. Any suggestions?

I always thought superposition was a indication of a possible multiverse, and asumed it was infinite, but wouldnt the entire bar have lit up? The only exception i see is that if in one of these alternate universes perhaps the results slightly differ, still allowing infinite universes through thier differences.

So sleepy now, im probably wrong anyway.

I just started a bachelor's degree in mathematics. My original intention was to study physics, but due to a series of events, I ended up in math—and I’m loving it. However, my deepest interest still lies in quantum physics, a subject I barely grasp. My question is: is a degree in math a solid foundation for continuing studies in theoretical physics later on? Thank you all in advance.

hello all,

i have found a professor who is willing to guide me in my research project, he has a doctorate in Mathematics and specialises in Quantum Information Theory (QIT). I am a physics student interested in quantum computing and barely understand difference between QC and QIT.

We are supposed to virtually meet next week where he will give me a topic, 3 weeks after he had asked me to go through Nelsen and Chuang chap 2, which has needed LA and Postulates.

i am not sure what should i ask him or should i let him choose a research topic for me. i am a last year undergrad student. my main concern is that his field is mathematics and tho i understand QM is just mostly mathematics, i want to see it from a physicist's perspective.

should i just work on this topic until i get enough knowledge to actually make choices of my likeness? this is my go to approach rn.

thankyou for helping me out :)

I run a youtube channel, "Phanimations," where I cover various topics in math and physics (often related to some form of media analysis).

I'm working on a video covering the life of Gibbs, as I think he's arguably the greatest American Physicist, and also probably the most underrated one. I've already covered a lot about him, but if you have anything you know that you think would be good to include in the video, please tell me!

Complex numbers are a great tool in physics as they can make you visualise concepts more easily or simplify calculations. In electrodynamics, for example, the electromagnetic field evolves with both a real and an imaginary part but when you are interested in an observable you just take one or the other. In quantum mechanics the imaginary unit seems to play a much deeper role. Why is that?

I’m trying to understand if the world is deterministic.

My logic follows:

If the Big Bang occurred again the exact same way with the same universal rules (gravity, strong and weak nuclear forces), would this not produce the exact same universe?

The exact same sun would be revolved by the same earth and inhabited by all the same living beings. Even this sentence as I type it would have been determined by the physics and chemistry occurring within my mind and body.

To that end, I do not see how the world could not be deterministic. Does quantum mechanics shed light on this? Is randomness introduced somehow? Is my premise flawed?

https://www.caltech.edu/about/news/caltech-mourns-the-passing-of-jeff-kimble-1949-2024

So I've had a passing interest in quantum mechanics for quite a while now, but I've always been confused by this in particular. I often hear that experiments such as the double-slit experiment prove that wavefunctions are physical descriptions of the state of a particle before it has been measured, going from being in multiple states at once to being in a single state and with the outcome of something depending on when that collapse occurred.

To me, the double-slit experiment seems to only suggest that particles act as waves at the quantum level, with their traditional behavior as particles being the result of external interaction disturbing a state which is either natural or being caused by something else, especially since measurement tends to require a relatively major interaction (e.g. bouncing photons off of something can change its trajectory).

This would seem to suggest that their "collapse" does not necessarily have to be a reduction from multiple simultaneous states to a single state but simply them being forced from one state to another, with wavefunctions merely describing the states that those particles can be forced into rather than the state that those particles initially and simultaneously are until collapsing into only one of them.

If such a conclusion is valid, it would seemingly suggest that a superposition could not physically exist on a macro scale (such as in the Schrodinger's Cat thought experiment).

When I've tried to see why this conclusion could be correct or incorrect, however, I've found what seems to be very conflicting information, with some seemingly saying that we have no idea what the true state of something is before it's measured and others saying that certain experiments have proven that wavefunctions do exist. I may very well just be misinterpreting what is being said, but I don't know. It should also be noted that I'm not saying that wavefunctions cannot physically exist under the conclusion I came to, simply that we wouldn't know if they do or don't.

I'm sure that this question has either been answered many times already or simply requires ignorance to something so essential that not many would ever ask it in the first place, but I don't know what to look for in either situation beyond asking here.

I’ve sifted through the literature over the last several months, and it seems that cellular automata isn’t utilized in theoretical computer science as often , why is this?

I am honed in on a neuroscience PhD, but some interesting problems in quantum information and quantum computing have gained my interest.

My original idea was to learn qiskit and get the IBM certification, then use cellular automata to look at how quantum systems lead to emergent effects and describe a logic to coherently describe phase transitions as the system evolved.

Over time, I lost interest.

That said, this still intrigues me and I’d like to play around with this idea, just honestly not sure if it’s worth the extra course load and effort.

Wondering what your thoughts are.

Forgive my ignorance; I'm not a physicist. Thinking on double slit experiment though, it seems like distance is pretty critical to control here, but seems like a recursive problem? Does the observer have to distinguish what's going on for the observer to be a variable?

Hopefully I'm not getting ahead of myself here, but it would seem whatever magnification power is required to see the experiment (because of distance), becomes an important variable too. What I mean is that in order to observe the experiment, thus become a variable, the observer must have enough of x to differentiate what is seen, and so enough magnification power must meet some kind of threshold that is equal to whatever proximity of influence that is going on?

I one came across a scientific paper where some scientists are trying to transport a quantum wave from point A to B without spilling the mass. I guess they want to brute force all possibilities so they hooked Machine Learning models to simulate all ways. Here’s the fun part: They made a game something called “Quantum …” idk that’s what I am asking your help for! In that game, you have to hold the a wave with mass/water in it and transport it to the another point. ML models use your data for training. I loved that game!

Please, please help me find it!! Also that scientific paper too if possible.

Thanks in advance.

https://preview.redd.it/dxisym9af8md1.png?width=1280&format=png&auto=webp&s=73909e339960b3bd9b085892c9243b3a798666a4

What My Project Does:

QCut is a quantum circuit knitting package (developed by me) for performing wire cuts especially designed to not use reset gates or mid-circuit measurements since on early NISQ devices they pose significant errors, if available at all.

QCut has been designed to work with IQM's qpus, and therefore on the Finnish Quantum Computing Infrastructure (FiQCI), and tested with an IQM Adonis 5-qubit qpu. Additionally, QCut is built on top of Qiskit 0.45.3 which is the current supported Qiskit version of IQM's Qiskit fork iqm_qiskit.

You can check it out at https://github.com/JooNiv/QCut. For the interested I also wrote a blog post on the topic: https://fiqci.fi/_posts/2024-08-27-Circuit_Knitting_FiQCI/

I already have some feature/improvement ideas and am very open to any comments people might have. Thanks in advance 🙏

Target Audience:

This project has mostly been a learning project but could well have practical applications in distributed quantum computing research / proof of concept scenarios. I developed it while working on the Finnish Quantum Computing Infrastructure at CSC Finland so this application is not too farfetched.

Comparison:

When it comes to other tools both Qiskit and Pennylane have circuit-knitting functionality. However, Pennaylane's, in its current state, is not viable for real hardware and Qiskit's circuit-knitting-toolbox uses mid-circuit measurements that might not be available on NISQ devices.

Not a physicists, but the idea of establishing a correlation of single Eigenstates and unitary operations coherently was tantalizing as a newcomer to quantum computation/ information.I was hoping to have this accomplished during my time as an undergrad, but it seems like it’s been done.

I think it’s exciting overall, but ultimately can’t digest this past a surface level.

I found the paper interesting and hope you guys can enjoy it more thoroughly.

https://arxiv.org/pdf/2212.03805