5 ms·

I don’t have a source to hand at the moment, but when I looked into the famous Delayed Choice Quantum Erasure experiment the consensus seemed to be: - The doub

I don’t have a source to hand at the moment, but when I looked into the famous Delayed Choice Quantum Erasure experiment the consensus seemed to be: - The double slit experiment’s conclusions still hold, but: - The particularly exciting and stark results of the Quantum Erasure experiment may have been misinterpreted or miscommunicated to the public, in particular: - The presenter of PBS SpaceTime has said that he regrets certain things about how he worded his video on the Quantum Erasure experiment, and I think may have left a comment on the video to that effect. Every time I look into QM, I keep coming back to the same fundamental axiom: “Quantum Mechanics’ weirdnesses can make otherwise straightforward things frustrating, but will never make interesting inventions possible.” Like how entanglement is able to break locality (which is frustrating) but without breaking causality (which would be interesting). If you hear about a quantum principle and think “Wow, I could use that to build X,” then it’s more likely that you’re not fully understanding the principle (not “you” specifically, I’ve fallen for this myself countless times). The only exception seems to be Quantum Computing, but even that only arises out of a deep deep mathematical analysis (you can’t get to QC on your own from the things in popular science books) and is only applicable to really niche applications.

thom 1y ago
It seems fairly obvious that the universe avoids doing work when it’s not necessary. I agree we’ll probably be disappointed looking for magical ways to make it yield much more.
naasking 1y ago
Entanglement doesn't violate locality, it's measurement that does that. And that's because we don't have a rigourous handle on what measurement actually is, and why we call it "the measurement problem"!
- westurner 1y ago
  Didn't they originally use polarizing filters to measure photonic phase? If it were possible to measure the phase of a photon after a beam splitter in a nondestructive way, shouldn't it be possible to determine whether measuring one causes state collapse in the other? This says that photonic entanglement is polarization, and that photonic phase can be inferred from second order of intensity, IIUC: "Bridging coherence optics and classical mechanics: A generic light polarization-entanglement complementary relation" (2023) https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.033110 https://journals.aps.org/prresearch/abstract/10.1103/PhysRev... Shouldn't it then be possible to nondestructively measure photons and thus entanglement?
  - naasking 1y ago
    > If it were possible to measure the phase of a photon after a beam splitter in a nondestructive way "Non-destructive measurement" is an oxymoron. It's not a real measurement if it doesn't destroy the coherence of entanglement. Weak measurements do destroy some entanglement, just not "all" of it.
    - westurner 1y ago
      > "Non-destructive measurement" is an oxymoron. It's not a real measurement if it doesn't destroy the coherence of entanglement. If there were no loopholes to Bell's theorem I would agree. > Weak measurements do destroy some entanglement, just not "all" of it. IDK if that's true. Are all methods of observing probabilistic states destructive forms of measurement? Does a camera on a candle diminish the candle, or does it take energy (and information) from the "wake" of the field moments or field disturbances? I don't think that anyone realizes that it's possible to infer photonic phase from intensity (by Huygens-Steiner).
      - westurner 1y ago
        > Weak measurements do destroy some entanglement, just not "all" of it. Which measure of degree of entanglement best characterizes state linkage across spacetime? Depending on definition, doesn't a laser pointer entangle phase states across spacetime, but only slower than c (the speed of transverse photonic waves in a total vacuum)? Are the states synchronized with a constant delay? Quantum discord: https://en.wikipedia.org/wiki/Quantum_discord https://en.wikipedia.org/wiki/Quantum_discord : > In quantum information theory, quantum discord is a measure of nonclassical correlations between two subsystems of a quantum system. It includes correlations that are due to quantum physical effects but do not necessarily involve quantum entanglement. Quantum mutual information: https://en.wikipedia.org/wiki/Quantum_mutual_information https://en.wikipedia.org/wiki/Quantum_mutual_information
whoknowsidont 1y ago
>about a quantum principle and think “Wow, I could use that to build X,” We use quantum principles to build things all the time. What are you talking about? https://en.wikipedia.org/wiki/Quantum_sensor#Research_and_applications https://en.wikipedia.org/wiki/Quantum_sensor#Research_and_ap... is just a few examples.
- Uehreka 1y ago
  I’m talking about building sexy things like ansibles or FTL engines. The kinds of transcendent ambitions that Quantum Mechanics often inspire in laypeople like me.
  - glitchc 1y ago
    Night vision goggles use quantum mechanics. Pretty sexy.
  - whoknowsidont 1y ago
    Even if we had a "stranglehold" on the deepest foundations of Quantum Mechanics it wouldn't help you with either of those things. In order for those things we need something beyond QM and a lot more grand. FTL travel and communication is in the ball park of relativity. QM is not an umbrella term for sci-fi.
  - stevenwoo 1y ago
    Every device one has that has integrated circuits (chips) and some of the discrete components was designed based on the quantum mechanical properties of materials that were beyond us until we understood quantum mechanics - sometimes we get too accustomed to the wonder right in front of us. The Electrical Engineering curriculum at my university started with Quantum Electrodynamics for a semester. Figuring out how the sun and stars work required an understanding of the smallest particles, it's all kind of amazing.
    - brookst 1y ago
      I don’t think it was intended to say that quantum effects are never useful. I interpreted the comment to mean that at at first glance quantum effects get things like instantaneous, FTL communications… but those most dramatic possibilities never work out when you dig deeper.
throw310822 1y ago
> The only exception seems to be Quantum Computing Yet so far it failed to do any useful work, correct? As I understand it, even the recent "quantum supremacy" results were about performing a humongous number of useless computations.
- jackmottatx 1y ago
  So far yes, but we should be able to in principle for a few kinds of problems.
- BoiledCabbage 1y ago
  It would be funny if this turned out to also apply to quantum computing. Ie while we can build a quantum computer, we can't actually find any productive problem that calculates faster than a classical algorithm. QC would turn out to be the biggest bust in physics (after string theory of course).
Devilspawn6666 1y ago
So you don't think a laser is an interesting invention? Those require quantum mechanics for the stimulated emission. Quantum tunneling is key to many devices as well. Then of course there's the reality that the mere existence of everything we see around us - the stability of atoms themselves - requires quantum mechanics.
baobun 1y ago
Quantum Enxryption!

thom 1y ago

It seems fairly obvious that the universe avoids doing work when it’s not necessary. I agree we’ll probably be disappointed looking for magical ways to make it yield much more.

naasking 1y ago

Entanglement doesn't violate locality, it's measurement that does that. And that's because we don't have a rigourous handle on what measurement actually is, and why we call it "the measurement problem"!

westurner 1y ago
Didn't they originally use polarizing filters to measure photonic phase? If it were possible to measure the phase of a photon after a beam splitter in a nondestructive way, shouldn't it be possible to determine whether measuring one causes state collapse in the other? This says that photonic entanglement is polarization, and that photonic phase can be inferred from second order of intensity, IIUC: "Bridging coherence optics and classical mechanics: A generic light polarization-entanglement complementary relation" (2023) https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.5.033110 https://journals.aps.org/prresearch/abstract/10.1103/PhysRev... Shouldn't it then be possible to nondestructively measure photons and thus entanglement?
- naasking 1y ago
  > If it were possible to measure the phase of a photon after a beam splitter in a nondestructive way "Non-destructive measurement" is an oxymoron. It's not a real measurement if it doesn't destroy the coherence of entanglement. Weak measurements do destroy some entanglement, just not "all" of it.
  - westurner 1y ago
    > "Non-destructive measurement" is an oxymoron. It's not a real measurement if it doesn't destroy the coherence of entanglement. If there were no loopholes to Bell's theorem I would agree. > Weak measurements do destroy some entanglement, just not "all" of it. IDK if that's true. Are all methods of observing probabilistic states destructive forms of measurement? Does a camera on a candle diminish the candle, or does it take energy (and information) from the "wake" of the field moments or field disturbances? I don't think that anyone realizes that it's possible to infer photonic phase from intensity (by Huygens-Steiner).
    - westurner 1y ago
      > Weak measurements do destroy some entanglement, just not "all" of it. Which measure of degree of entanglement best characterizes state linkage across spacetime? Depending on definition, doesn't a laser pointer entangle phase states across spacetime, but only slower than c (the speed of transverse photonic waves in a total vacuum)? Are the states synchronized with a constant delay? Quantum discord: https://en.wikipedia.org/wiki/Quantum_discord https://en.wikipedia.org/wiki/Quantum_discord : > In quantum information theory, quantum discord is a measure of nonclassical correlations between two subsystems of a quantum system. It includes correlations that are due to quantum physical effects but do not necessarily involve quantum entanglement. Quantum mutual information: https://en.wikipedia.org/wiki/Quantum_mutual_information https://en.wikipedia.org/wiki/Quantum_mutual_information

whoknowsidont 1y ago

>about a quantum principle and think “Wow, I could use that to build X,” We use quantum principles to build things all the time. What are you talking about? https://en.wikipedia.org/wiki/Quantum_sensor#Research_and_applications https://en.wikipedia.org/wiki/Quantum_sensor#Research_and_ap... is just a few examples.

Uehreka 1y ago
I’m talking about building sexy things like ansibles or FTL engines. The kinds of transcendent ambitions that Quantum Mechanics often inspire in laypeople like me.
- glitchc 1y ago
  Night vision goggles use quantum mechanics. Pretty sexy.
- whoknowsidont 1y ago
  Even if we had a "stranglehold" on the deepest foundations of Quantum Mechanics it wouldn't help you with either of those things. In order for those things we need something beyond QM and a lot more grand. FTL travel and communication is in the ball park of relativity. QM is not an umbrella term for sci-fi.
- stevenwoo 1y ago
  Every device one has that has integrated circuits (chips) and some of the discrete components was designed based on the quantum mechanical properties of materials that were beyond us until we understood quantum mechanics - sometimes we get too accustomed to the wonder right in front of us. The Electrical Engineering curriculum at my university started with Quantum Electrodynamics for a semester. Figuring out how the sun and stars work required an understanding of the smallest particles, it's all kind of amazing.
  - brookst 1y ago
    I don’t think it was intended to say that quantum effects are never useful. I interpreted the comment to mean that at at first glance quantum effects get things like instantaneous, FTL communications… but those most dramatic possibilities never work out when you dig deeper.

throw310822 1y ago

> The only exception seems to be Quantum Computing Yet so far it failed to do any useful work, correct? As I understand it, even the recent "quantum supremacy" results were about performing a humongous number of useless computations.

jackmottatx 1y ago
So far yes, but we should be able to in principle for a few kinds of problems.
BoiledCabbage 1y ago
It would be funny if this turned out to also apply to quantum computing. Ie while we can build a quantum computer, we can't actually find any productive problem that calculates faster than a classical algorithm. QC would turn out to be the biggest bust in physics (after string theory of course).

Devilspawn6666 1y ago

So you don't think a laser is an interesting invention? Those require quantum mechanics for the stimulated emission. Quantum tunneling is key to many devices as well. Then of course there's the reality that the mere existence of everything we see around us - the stability of atoms themselves - requires quantum mechanics.

baobun 1y ago

Quantum Enxryption!