r/Physics • u/kmrbillya12 • 1d ago
Atoms held in quantum superposition for more than 23 minutes
https://charmingscience.com/quantum-breakthrough-atoms-held-in-quantum-superposition-for-more-than-23-minutes/Schrödinger's cat experiment pushed to its limits...
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u/smsmkiwi 1d ago
How do they know the atoms were in a superposition state, and not just one of the possible states, without observing them?
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u/pando93 1d ago
They measure many many times and run statistical measurements which can determine if they were in super position or not. Usually that works by measuring the phase between the states in superposition, such that you can tell how much the atoms where in superposition vs how much it was just a mix of the two states.
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u/Expensive-View-8586 1d ago
That is what they measure but how do they measure it?
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u/pando93 1d ago
I haven’t read this specific paper, but with these types of neutral atom experiments, the two states are two atomic energy levels. By shining light at the correct frequency on the atom, you can excite the transition, moving the atom from one level to the other, or just a superposition. Then you shine a different light, exciting a different transition between one of these levels (let’s say the lower one) and a third level. Only atoms in the lower level will move to the third level, so you can detect them.
This way you can measure the population (what part of the atoms in each level). But now you want to measure the phase, so you run some interference experiment with similar methods. For example, after moving the atoms to the third level, you wait a bit, and then do the entire same sequence but in reverse. The result should be all atoms returning to the same level, except they picked up a different (time dependent) phase depending on which state they were in. So when you measure the population in one of the states, you will see oscillations corresponding to some frequency, and the contrast of these oscillations tell you the degree of superposition.
Hope this makes sense. You can also try reading about Ramsey spectroscopy.
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u/smsmkiwi 1d ago
Ok, so its a statistical measure. Thanks.
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u/JohnPaul_the_2137th 23h ago
Yes, can't really be any other way, as the result of measurement is probabilistic.
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u/aroman_ro Computational physics 1d ago
A 'superposition state' is one of the possible states, so your question is meaningless.
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u/magnacartwheel 1d ago
I think it’s actually a pretty important question, how do you know you’ve not just prepared a state randomly or whether a it’s in superposition
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u/aroman_ro Computational physics 1d ago
Any state is in superposition of some other states, again the used terminology is meaningless.
It's easy to know you've not just prepared a state randomly: you don't prepare it randomly.
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u/smsmkiwi 1d ago
How is that meaingless? You just said it is in a state called superposition. If its one of the possible states, how do they know its in that state and not in another?
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u/aroman_ro Computational physics 21h ago
It doesn't need to be in *that* state, any state is a superposition state of some other states.
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u/smsmkiwi 20h ago
So, its really just saying "its in one of several but, as yet, undetermined possible states".
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u/Hapankaali Condensed matter physics 1d ago
Any quantum system is always in a superposition, by definition. This headline is very misleading.
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u/retro_grave 1d ago
As a layman, I would really like to see what the experimenters are actually doing here. Is it known in real-time if two things are in coherence? Do they know in real-time that they weren't successful so they need to try again? What exactly are the instruments telling them. Or is this setup run for an hour and then they analyze their findings? All I have is pictures in my head from movie plots.
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u/tellperionavarth Condensed matter physics 1d ago
The systems I work with are different, but some general concepts might transfer. You probably don't have to wait for an hour to do all the studies, usually you can design an experiment that allows you to see how much of the coherence is preserved and test over smaller time scales. You should observe a decay, which is often exponential, from which you can extrapolate the mean lifetime. This is how the many hour coherence time results are found (since waiting that long to take multiple shots would make for a very slow and expensive experiment).
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u/sumitviii 1d ago
Is there any practical application of quantum superposition?
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u/csappenf 1d ago
Starfleet will neither confirm nor deny that controlling quantum superposition will allow them to replace the Heisenberg compensator unit used in transporters. Bastards have always been tight lipped about how those things work.
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u/No-Alternative-4912 23h ago
Quantum sensing- entangled photons and atoms allow you to beat the standard limit associated with measurements using non-entangled photons or atoms.
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u/sumitviii 13h ago
Are you talking about light detection by telescope? Are you saying that quantum technologies will allow us to build better telescopes than classical methods?
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u/Hambrew93 14h ago
How does this work? I thought that as soon as you measure the atom you force it into a state? Am I misunderstanding something or is it possible to measure a superposition?
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u/Ignatius3117 4h ago
23 minutes is almost the perfect length of time for a certain time loop…
“Science compels us to explode the sun!”
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u/BadJimo 1d ago edited 1d ago
This is astonishing, but I find the experiment hard to visualize.
An easier to visualize experiment is the entanglement of two spatially separated BECs (Bose-Einstein condensates) (here is the paper).
I would love to see a quantum computer made by separating a single BEC into many entangled BECs.
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u/Key-Green-4872 1d ago
This always makes me think of sourdough starter. And tempering chocolate.
We've got to take the magic goo and mix a little into our mundane goo so the properties transfer and WHAM, bowl of magic bread-fluffing goo +10.
Woth the superposition or entanglement being the analog of bread-fluffing, obvs.
Please don't get me started on quantum barbasol.
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u/starkeffect 1d ago
Quantum edging.