18 ms·

Computer scientists prove that heat destroys quantum entanglement

178 points by isaacfrond 2y ago

GolDDranks 2y ago
See also: https://news.ycombinator.com/item?id=41380888 https://news.ycombinator.com/item?id=41380888
gradschoolfail 2y ago
For practitioners, a rough description of their argument is on pg 7 (note: separable=unentangled, β =1/kb T) of https://arxiv.org/pdf/2403.16850 https://arxiv.org/pdf/2403.16850 This state [rho] is the Gibbs state at infinite temperature, and is in the interior of the convex hull of product states. So, as β tends to zero, ρ will eventually enter the interior of this convex hull, making it separable. This happens at a finite β which depends on system size.
- marginalia_nu 2y ago
  Been a while since I've been working in the field, but wouldn't we expect this finding through the model of dissipation and decoherence? Seems like Caldeira & Leggett all over again.
  - gradschoolfail 2y ago
    Hmm, C&L argument involves taking a classical limit, does it not? This paper seems “fully quantum” (provided that you agree that the maximally mixed “Gibbs” state should not be considered a “classical” limit, only an infinite temp limit)
    - marginalia_nu 2y ago
      Yeah maybe that's what's bothering me, what is the high temperature limit if not the classical limit?
      - gradschoolfail 2y ago
        Heh, you might be additionally bothered that for the C&L model, the strong coupling (to heat bath) limit can also be considered the (/a?) classical limit, e.g. https://arxiv.org/pdf/1603.07495 https://arxiv.org/pdf/1603.07495
  - gautampk 2y ago
    I think the naive expectation would be that a hot state would be highly entangled and non-separable. The non-separability is what leads to decoherence when you do a partial trace. You can arbitrarily split any multi-part Hilbert space into a "system" and an "environment" and then trace out the environment. If they are highy entangled with one another then the resulting system-without-environment will be decohered.
    - gradschoolfail 2y ago
      Alternatively formulated, this suggests that an entangled state, if weakly coupled to a bath at high temperature and allowed to thermalize, will become fully disentangled at a finite time. (p1) hinting that something different is happening here (from the C&L model mentioned below.) Indeed the CS guys are probably looking for a way to redefine entanglement (entropy, as you summarized above), to essentially “work” in the same way as what they have in their preprint, but also cover the prethermalized cases..
danbruc 2y ago
A similar result for superposition would be huge, I guess, after a century we could finally understand what qualifies as a measurement device, why we do not observe quantum effects at macroscopic scales, what actually saves or kills Schrödinger's cat.
- sebzim4500 2y ago
  There's a result in quantum information that demonstrating a superposition of two states is at least as hard as switching between those states. So designing an experiment to show that a cat is in a superposition of alive and dead is at least as hard as bringing a dead cat back to life (obviously in real life it would be much harder, this is just a lower bound).
  - Obscurity4340 2y ago
    Isn't the cat experiment bullshit outside of illustrating a macro version of this? Like, there's no superposition in reality or the cat is too big to be subject to quantum mechanics where these shenanigans happen or something?
    - deleted 2y ago
      [deleted]
    - hiciu 2y ago
      The cat isn't in some quantum state. Cat is locked in a box, with some poison and a Geiger counter. Poison is released when Geiger counter registers a particle. Now, the process of atom decay that would be registered by a Geiger counter has some interesting properties and that's where the "quantum magic" happens. (at least, that's my mental model of it; ask an expert, I'm not an expert)
      - immibis 2y ago
        The quantum magic properties are thought to transfer to the poison and the cat.
Gooblebrai 2y ago
How do they come up with those amazing illustrations? Quanta Magazine always impresses me with the illustrations for each article
- klysm 2y ago
  I’d assuming paying and working with good artists
- noname120 2y ago
  Which illustrations are you referring to? I only see one illustration (at the top) and it looks like AI-grade material.
  - mandmandam 2y ago
    I'm guess they're referring to the illustration that's clearly attributed to Quanta's Visual Designer Kristina Armitage. The illustration matches the tone and content of the piece, while also being visually consistent with her other Quanta illustrations. Seems like Ms. Armitage is only 2 years out of college, but is literally (illustratively?) crushing it [0]. Knee-jerk criticism like this in response to someone putting out heart-felt praise is so, so unnecessary. There's a time for putting down AI-assisted work, maybe, but this isn't it. 0 - https://www.behance.net/moodboard/179460311/illustration https://www.behance.net/moodboard/179460311/illustration
    - EGreg 2y ago
      When is there ever a time for putting down AI assisted work? Serious question.
      - mandmandam 2y ago
        I can think of a few situations... Like when it's flooding your board / group with ultra-low-effort crap, or when it's clearly a barely-digested regurgitation of an artist's style that they spent decades developing at great personal cost. When it's used to scam people, or when it's used to smear them. I find it upsetting that a company can steal the essence of thousands / millions of people's life's work, "transform" it with an algorithm, and then sell it to people without any recognition of the theft whatsoever. I don't like that a generation of creatives is being undercut, all during a time when inequality and wealth capture are rampant due to out-of-control mega-corporations - which immediately make moves to buy and/or copy said company... Like, I love creativity. I love AI. I think AI will be a part of our future whether we moan about it or not. At the same time, the world is awash with the worst type of scams, to the point where making a living is hard even if you work a steady 9-5. Even if you work two. Damn near every artist, writer, musician is scrabbling ridiculously hard to stay afloat as it is. Some aren't making it. I can see why they're pissed. And I think that for the most part, being angry at 'AI' is pointless, except as a means to distract from the true parasites of our age.
wizardforhire 2y ago
For those interested in some quantum stuff and interested in watching a kindred spirit do approachable practical experiments I highly advise watching this guys stuff [1]. Consider it a psa [1] https://youtube.com/@HuygensOptics https://youtube.com/@HuygensOptics
- altruios 2y ago
  I have the suspicion that there are several very simple experiments we have yet to think up that would give incredible revelations with the inner workings quantum mechanics. I have a mental model for entanglement that's probably very wrong, and I would love to devise a proper test to falsify it.
cma 2y ago
Something related from the og computer scientist, though does their new result have impacts on the quantum zeno effect? [I]t is easy to show using standard theory that if a system starts in an eigenstate of some observable, and measurements are made of that observable N times a second, then, even if the state is not a stationary one, the probability that the system will be in the same state after, say, one second, tends to one as N tends to infinity; that is, that continual observations will prevent motion. Alan and I tackled one or two theoretical physicists with this, and they rather pooh-poohed it by saying that continual observation is not possible. But there is nothing in the standard books (e.g., Dirac's) to this effect, so that at least the paradox shows up an inadequacy of Quantum Theory as usually presented. — Quoted by Andrew Hodges in Mathematical Logic, R. O. Gandy and C. E. M. Yates, eds. (Elsevier, 2001), p. 267. > As a result of Turing's suggestion, the quantum Zeno effect is also sometimes known as the Turing paradox.
thelittlenag 2y ago
What is the implication for high temperature superconductors? Does this mean that they can't exist?
6d6b73 2y ago
Some day, when I have moree time, I will work on proving my theory that the entanglement doesn't really exist, and the whole quantum weirdness is just bs. But know I have to finish coding that data acquisition system. Priorities..
- HideousKojima 2y ago
  Kind of like my plan to prove flat earthers wrong using long range rifles and the Coriolis effect at different places north and south of the equator, still waiting on Argentina to give me permission to bring a bunch of rifles to Tierra del Fuego.
  - me_me_me 2y ago
    coincidentally the flat earth movement is imploding a bit, as their 'thought' leaders were invited to visit the south pole to observe 24h day as witnesses. A thing technically impossible for flat earth 'model'. But they just started attacking each other as not reliable enough to go. Anyhow they would claim time near the edges slows down the time or the whole thing was a virtual 3d future tech used to fool them
    - HideousKojima 2y ago
      >coincidentally the flat earth movement is imploding a bit, as their 'thought' leaders were invited to visit the south pole to observe 24h day as witnesses. Got a link? That sounds hilarious but I couldn't find any articles about it (though I didn't search terribly hard).
      - recursivecaveat 2y ago
        I found this which is I think what they were referring to: https://www.the-final-experiment.com/ https://www.the-final-experiment.com/
        me_me_me 2y ago
misja111 2y ago
Isn't heat transmitted by photons? In that case, isn't it inevitable that heat destroys entanglement? Because the transmission of heat means some photon has to interact with one of the entangled particles.
- kdsch 2y ago
  you’re thinking of radiant heat. There’s also heating by conduction
  - ryandamm 2y ago
    … which is usually mediated by electric field interactions, involving virtual photons. Right?
    - dgfitz 2y ago
      Isn't that induction? Asking as I am not sure.
      - itishappy 2y ago
        Great question! It's literally all the same process! There's only a difference on a macroscopic scale. On an atomic scale, atoms are tiny vibrating charges held together (and apart!) by electric forces (well, by all forces, but the electric force is by far the strongest). A vibrating charge can emit a photon; we call this radiation. This radiation can be reabsorbed somewhere and induce a new vibration. This is technically induction (though I've never seen it referred to as such, more commonly radiative transfer). If we step back so that we no longer view individual atoms, we just see vibrations moving around within a material; we call this conduction but it's still happening via radiative transfer. If your material is a fluid and moves around for some heat-related reason (say, a change in density), we call this convection. https://en.wikipedia.org/wiki/Radiative_transfer https://en.wikipedia.org/wiki/Radiative_transfer Confusingly, inductive heating is a completely different process involving no heat transfer! You induce a current in material, and this current causes resistive heating. https://en.wikipedia.org/wiki/Induction_heating https://en.wikipedia.org/wiki/Induction_heating You might be wondering: "then what's resistive heating?" Well, electrons are also tiny moving charges. Care to hazard a guess how they interact with their environment?
rocqua 2y ago
I have heard, and like, the theory that 'waveform collapse' due to 'observation' is due to entaglement. Specifically, the idea is that most of the world is quantum entangled, 'observation' then has the effect of entangling the observed particle with 'most of the world'. The 'waveform collapse' is then the result of this entaglement with everything causing the waveform to concentrate heavily. Is this concept debunked by this paper, or could it be that 'destroys entanglement' actually means 'becomes entangled with almost everything else'?
- deleted 2y ago
  [deleted]
- rcxdude 2y ago
  It's consistent with that interpretation (which is actually the line of reasoning which leads to the many-worlds interpretation). What it shows is that if you take the quantum description of the state of the system, above a certain temperature it turns into a state which can be described as if it were multiple overlapping systems which can be explained purely classically (i.e. no entanglement wierdness). This is what many-worlds is derived from: if you model a quantum system interacting with a big and hot system, you will find that for each outcome of 'collapse', there is a part of the resulting quantum state that corresponds to that observation, and it doesn't interact further with the opposite state. Hence the interpretation that actually the waveform never collapses, it's just the states of the measurement apparatus and the people running it seperate into two states that cease to interact (i.e. many 'parallel universes' inside the same wavefunction: they weren't made up just for fun).
  - rocqua 2y ago
    So many-worlds says that the waveform doesn't collapse to a kronecker-delta, but to an average of multiple ones that 'don't interact'. Is this conjecture, do we see this in some specific toy systems, or do we know this is how all 'collapsed' waveforms behave? In other words, to what degree is the many-worlds interpretation just an interpretation of the waveform, or is it also a conjecture about how the waveform behaves? edit: it also sounds like the 'many worlds' are separate, but the 'real' waveform actually still has the information of all the worlds. That suggests the information in that waveform is huge. It also feels like the 'non-collapsed' things from the different worlds could still interact. How much of what I said here is wrong (I presume it is a lot)?
swayvil 2y ago
I skimmed 5 pages down looking for the darn temperature of disentanglement with no luck. Could one of you more perseverant readers enlighten me?
adolph 2y ago
<ctl>+f entropy didn't return anything, so I went looking for the paper. It looks like it is: "High-Temperature Gibbs States are Unentangled and Efficiently Preparable" [0] but maybe it is "Structure learning of Hamiltonians from real-time evolution" [1] 0. https://arxiv.org/abs/2403.16850 https://arxiv.org/abs/2403.16850 1. https://arxiv.org/abs/2405.00082 https://arxiv.org/abs/2405.00082
GlibMonkeyDeath 2y ago
Please note that the entanglement here are on spin states in equilibrium with a mean temperature bath - this doesn't apply to e.g. a pair of (or sets of) entangled photons (which aren't interacting with anything on the way to the detectors.)

178 points by isaacfrond 2y ago

See also: https://news.ycombinator.com/item?id=41380888 https://news.ycombinator.com/item?id=41380888

For practitioners, a rough description of their argument is on pg 7 (note: separable=unentangled, β =1/kb T) of https://arxiv.org/pdf/2403.16850 https://arxiv.org/pdf/2403.16850 This state [rho] is the Gibbs state at infinite temperature, and is in the interior of the convex hull of product states. So, as β tends to zero, ρ will eventually enter the interior of this convex hull, making it separable. This happens at a finite β which depends on system size.

marginalia_nu 2y ago
Been a while since I've been working in the field, but wouldn't we expect this finding through the model of dissipation and decoherence? Seems like Caldeira & Leggett all over again.
- gradschoolfail 2y ago
  Hmm, C&L argument involves taking a classical limit, does it not? This paper seems “fully quantum” (provided that you agree that the maximally mixed “Gibbs” state should not be considered a “classical” limit, only an infinite temp limit)
  - marginalia_nu 2y ago
    Yeah maybe that's what's bothering me, what is the high temperature limit if not the classical limit?
    - gradschoolfail 2y ago
      Heh, you might be additionally bothered that for the C&L model, the strong coupling (to heat bath) limit can also be considered the (/a?) classical limit, e.g. https://arxiv.org/pdf/1603.07495 https://arxiv.org/pdf/1603.07495
- gautampk 2y ago
  I think the naive expectation would be that a hot state would be highly entangled and non-separable. The non-separability is what leads to decoherence when you do a partial trace. You can arbitrarily split any multi-part Hilbert space into a "system" and an "environment" and then trace out the environment. If they are highy entangled with one another then the resulting system-without-environment will be decohered.
  - gradschoolfail 2y ago
    Alternatively formulated, this suggests that an entangled state, if weakly coupled to a bath at high temperature and allowed to thermalize, will become fully disentangled at a finite time. (p1) hinting that something different is happening here (from the C&L model mentioned below.) Indeed the CS guys are probably looking for a way to redefine entanglement (entropy, as you summarized above), to essentially “work” in the same way as what they have in their preprint, but also cover the prethermalized cases..

danbruc 2y ago

A similar result for superposition would be huge, I guess, after a century we could finally understand what qualifies as a measurement device, why we do not observe quantum effects at macroscopic scales, what actually saves or kills Schrödinger's cat.

sebzim4500 2y ago
There's a result in quantum information that demonstrating a superposition of two states is at least as hard as switching between those states. So designing an experiment to show that a cat is in a superposition of alive and dead is at least as hard as bringing a dead cat back to life (obviously in real life it would be much harder, this is just a lower bound).
- Obscurity4340 2y ago
  Isn't the cat experiment bullshit outside of illustrating a macro version of this? Like, there's no superposition in reality or the cat is too big to be subject to quantum mechanics where these shenanigans happen or something?
  - deleted 2y ago
    [deleted]
  - hiciu 2y ago
    The cat isn't in some quantum state. Cat is locked in a box, with some poison and a Geiger counter. Poison is released when Geiger counter registers a particle. Now, the process of atom decay that would be registered by a Geiger counter has some interesting properties and that's where the "quantum magic" happens. (at least, that's my mental model of it; ask an expert, I'm not an expert)
    - immibis 2y ago
      The quantum magic properties are thought to transfer to the poison and the cat.

Gooblebrai 2y ago

How do they come up with those amazing illustrations? Quanta Magazine always impresses me with the illustrations for each article

klysm 2y ago
I’d assuming paying and working with good artists
noname120 2y ago
Which illustrations are you referring to? I only see one illustration (at the top) and it looks like AI-grade material.
- mandmandam 2y ago
  I'm guess they're referring to the illustration that's clearly attributed to Quanta's Visual Designer Kristina Armitage. The illustration matches the tone and content of the piece, while also being visually consistent with her other Quanta illustrations. Seems like Ms. Armitage is only 2 years out of college, but is literally (illustratively?) crushing it [0]. Knee-jerk criticism like this in response to someone putting out heart-felt praise is so, so unnecessary. There's a time for putting down AI-assisted work, maybe, but this isn't it. 0 - https://www.behance.net/moodboard/179460311/illustration https://www.behance.net/moodboard/179460311/illustration
  - EGreg 2y ago
    When is there ever a time for putting down AI assisted work? Serious question.
    - mandmandam 2y ago
      I can think of a few situations... Like when it's flooding your board / group with ultra-low-effort crap, or when it's clearly a barely-digested regurgitation of an artist's style that they spent decades developing at great personal cost. When it's used to scam people, or when it's used to smear them. I find it upsetting that a company can steal the essence of thousands / millions of people's life's work, "transform" it with an algorithm, and then sell it to people without any recognition of the theft whatsoever. I don't like that a generation of creatives is being undercut, all during a time when inequality and wealth capture are rampant due to out-of-control mega-corporations - which immediately make moves to buy and/or copy said company... Like, I love creativity. I love AI. I think AI will be a part of our future whether we moan about it or not. At the same time, the world is awash with the worst type of scams, to the point where making a living is hard even if you work a steady 9-5. Even if you work two. Damn near every artist, writer, musician is scrabbling ridiculously hard to stay afloat as it is. Some aren't making it. I can see why they're pissed. And I think that for the most part, being angry at 'AI' is pointless, except as a means to distract from the true parasites of our age.

wizardforhire 2y ago

For those interested in some quantum stuff and interested in watching a kindred spirit do approachable practical experiments I highly advise watching this guys stuff [1]. Consider it a psa [1] https://youtube.com/@HuygensOptics https://youtube.com/@HuygensOptics

altruios 2y ago
I have the suspicion that there are several very simple experiments we have yet to think up that would give incredible revelations with the inner workings quantum mechanics. I have a mental model for entanglement that's probably very wrong, and I would love to devise a proper test to falsify it.

cma 2y ago

Something related from the og computer scientist, though does their new result have impacts on the quantum zeno effect? [I]t is easy to show using standard theory that if a system starts in an eigenstate of some observable, and measurements are made of that observable N times a second, then, even if the state is not a stationary one, the probability that the system will be in the same state after, say, one second, tends to one as N tends to infinity; that is, that continual observations will prevent motion. Alan and I tackled one or two theoretical physicists with this, and they rather pooh-poohed it by saying that continual observation is not possible. But there is nothing in the standard books (e.g., Dirac's) to this effect, so that at least the paradox shows up an inadequacy of Quantum Theory as usually presented. — Quoted by Andrew Hodges in Mathematical Logic, R. O. Gandy and C. E. M. Yates, eds. (Elsevier, 2001), p. 267. > As a result of Turing's suggestion, the quantum Zeno effect is also sometimes known as the Turing paradox.

thelittlenag 2y ago

What is the implication for high temperature superconductors? Does this mean that they can't exist?

6d6b73 2y ago

Some day, when I have moree time, I will work on proving my theory that the entanglement doesn't really exist, and the whole quantum weirdness is just bs. But know I have to finish coding that data acquisition system. Priorities..

HideousKojima 2y ago
Kind of like my plan to prove flat earthers wrong using long range rifles and the Coriolis effect at different places north and south of the equator, still waiting on Argentina to give me permission to bring a bunch of rifles to Tierra del Fuego.
- me_me_me 2y ago
  coincidentally the flat earth movement is imploding a bit, as their 'thought' leaders were invited to visit the south pole to observe 24h day as witnesses. A thing technically impossible for flat earth 'model'. But they just started attacking each other as not reliable enough to go. Anyhow they would claim time near the edges slows down the time or the whole thing was a virtual 3d future tech used to fool them
  - HideousKojima 2y ago
    >coincidentally the flat earth movement is imploding a bit, as their 'thought' leaders were invited to visit the south pole to observe 24h day as witnesses. Got a link? That sounds hilarious but I couldn't find any articles about it (though I didn't search terribly hard).
    - recursivecaveat 2y ago
      I found this which is I think what they were referring to: https://www.the-final-experiment.com/ https://www.the-final-experiment.com/
      - me_me_me 2y ago

misja111 2y ago

Isn't heat transmitted by photons? In that case, isn't it inevitable that heat destroys entanglement? Because the transmission of heat means some photon has to interact with one of the entangled particles.

kdsch 2y ago
you’re thinking of radiant heat. There’s also heating by conduction
- ryandamm 2y ago
  … which is usually mediated by electric field interactions, involving virtual photons. Right?
  - dgfitz 2y ago
    Isn't that induction? Asking as I am not sure.
    - itishappy 2y ago
      Great question! It's literally all the same process! There's only a difference on a macroscopic scale. On an atomic scale, atoms are tiny vibrating charges held together (and apart!) by electric forces (well, by all forces, but the electric force is by far the strongest). A vibrating charge can emit a photon; we call this radiation. This radiation can be reabsorbed somewhere and induce a new vibration. This is technically induction (though I've never seen it referred to as such, more commonly radiative transfer). If we step back so that we no longer view individual atoms, we just see vibrations moving around within a material; we call this conduction but it's still happening via radiative transfer. If your material is a fluid and moves around for some heat-related reason (say, a change in density), we call this convection. https://en.wikipedia.org/wiki/Radiative_transfer https://en.wikipedia.org/wiki/Radiative_transfer Confusingly, inductive heating is a completely different process involving no heat transfer! You induce a current in material, and this current causes resistive heating. https://en.wikipedia.org/wiki/Induction_heating https://en.wikipedia.org/wiki/Induction_heating You might be wondering: "then what's resistive heating?" Well, electrons are also tiny moving charges. Care to hazard a guess how they interact with their environment?

rocqua 2y ago

I have heard, and like, the theory that 'waveform collapse' due to 'observation' is due to entaglement. Specifically, the idea is that most of the world is quantum entangled, 'observation' then has the effect of entangling the observed particle with 'most of the world'. The 'waveform collapse' is then the result of this entaglement with everything causing the waveform to concentrate heavily. Is this concept debunked by this paper, or could it be that 'destroys entanglement' actually means 'becomes entangled with almost everything else'?

deleted 2y ago
[deleted]
rcxdude 2y ago
It's consistent with that interpretation (which is actually the line of reasoning which leads to the many-worlds interpretation). What it shows is that if you take the quantum description of the state of the system, above a certain temperature it turns into a state which can be described as if it were multiple overlapping systems which can be explained purely classically (i.e. no entanglement wierdness). This is what many-worlds is derived from: if you model a quantum system interacting with a big and hot system, you will find that for each outcome of 'collapse', there is a part of the resulting quantum state that corresponds to that observation, and it doesn't interact further with the opposite state. Hence the interpretation that actually the waveform never collapses, it's just the states of the measurement apparatus and the people running it seperate into two states that cease to interact (i.e. many 'parallel universes' inside the same wavefunction: they weren't made up just for fun).
- rocqua 2y ago
  So many-worlds says that the waveform doesn't collapse to a kronecker-delta, but to an average of multiple ones that 'don't interact'. Is this conjecture, do we see this in some specific toy systems, or do we know this is how all 'collapsed' waveforms behave? In other words, to what degree is the many-worlds interpretation just an interpretation of the waveform, or is it also a conjecture about how the waveform behaves? edit: it also sounds like the 'many worlds' are separate, but the 'real' waveform actually still has the information of all the worlds. That suggests the information in that waveform is huge. It also feels like the 'non-collapsed' things from the different worlds could still interact. How much of what I said here is wrong (I presume it is a lot)?

swayvil 2y ago

I skimmed 5 pages down looking for the darn temperature of disentanglement with no luck. Could one of you more perseverant readers enlighten me?

adolph 2y ago

<ctl>+f entropy didn't return anything, so I went looking for the paper. It looks like it is: "High-Temperature Gibbs States are Unentangled and Efficiently Preparable" [0] but maybe it is "Structure learning of Hamiltonians from real-time evolution" [1] 0. https://arxiv.org/abs/2403.16850 https://arxiv.org/abs/2403.16850 1. https://arxiv.org/abs/2405.00082 https://arxiv.org/abs/2405.00082

GlibMonkeyDeath 2y ago

Please note that the entanglement here are on spin states in equilibrium with a mean temperature bath - this doesn't apply to e.g. a pair of (or sets of) entangled photons (which aren't interacting with anything on the way to the detectors.)