12 ms·

Two atomic clocks have been quantum entangled for the first time

168 points by lysp 4y ago

dtx1 4y ago
paywalled. 12ft.io doesnt help.
- alexalx666 4y ago
  12ft is awesome, thanks!
- axiolite 4y ago
  Full article: http://webcache.googleusercontent.com/search?hl=en&q=cache%3Ahttps%3A%2F%2Fwww.newscientist.com%2Farticle%2F2337042%2Dtwo%2Datomic%2Dclocks%2Dhave%2Dbeen%2Dquantum%2Dentangled%2Dfor%2Dthe%2Dfirst%2Dtime%2F http://webcache.googleusercontent.com/search?hl=en&q=cache%3...
kalupa 4y ago
https://archive.ph/VVwbl https://archive.ph/VVwbl EDIT: ah, dang, also doesn't work
colejohnson66 4y ago
From /r/science[0]: https://news.mit.edu/2020/atomic-clock-time-precise-1216 https://news.mit.edu/2020/atomic-clock-time-precise-1216 [0]: https://old.reddit.com/r/science/comments/x8khxg/two_atomic_clocks_have_been_quantum_entangled_for/injginb/?context=3 https://old.reddit.com/r/science/comments/x8khxg/two_atomic_...
rolph 4y ago
MIT news: https://news.mit.edu/2020/atomic-clock-time-precise-1216 https://news.mit.edu/2020/atomic-clock-time-precise-1216 seems to be the better link, also reveals subject is a 2020 discovery, was also published in Nature: https://www.nature.com/articles/s41586-022-05088-z https://www.nature.com/articles/s41586-022-05088-z [paywall] "Abstract Optical atomic clocks are our most precise tools to measure time and frequency1,2,3. Precision frequency comparisons between clocks in separate locations enable one to probe the space–time variation of fundamental constants4,5 and the properties of dark matter6,7, to perform geodesy8,9,10 and to evaluate systematic clock shifts. Measurements on independent systems are limited by the standard quantum limit; measurements on entangled systems can surpass the standard quantum limit to reach the ultimate precision allowed by quantum theory—the Heisenberg limit. Although local entangling operations have demonstrated this enhancement at microscopic distances11,12,13,14,15,16, comparisons between remote atomic clocks require the rapid generation of high-fidelity entanglement between systems that have no intrinsic interactions. Here we report the use of a photonic link17,18 to entangle two 88Sr+ ions separated by a macroscopic distance19 (approximately 2 m) to demonstrate an elementary quantum network of entangled optical clocks. For frequency comparisons between the ions, we find that entanglement reduces the measurement uncertainty by nearly \(\sqrt{2}\), the value predicted for the Heisenberg limit. Today’s optical clocks are typically limited by dephasing of the probe laser20; in this regime, we find that entanglement yields a factor of 2 reduction in the measurement uncertainty compared with conventional correlation spectroscopy techniques20,21,22. We demonstrate this enhancement for the measurement of a frequency shift applied to one of the clocks. This two-node network could be extended to additional nodes23, to other species of trapped particles or—through local operations—to larger entangled systems. "
- clouddrover 4y ago
  The New Scientist article is talking about network of two entangled optical atomic clocks, which is a step beyond entanglement within one clock. Here's what Oxford's physics department says about it: https://www.physics.ox.ac.uk/news/quantum-network-entangled-atomic-clocks https://www.physics.ox.ac.uk/news/quantum-network-entangled-...
amelius 4y ago
> Two atomic clocks have been connected using quantum entanglement – a property that intrinsically links them so that changes in one instantaneously affect the other. Not this explanation again ...
- rco8786 4y ago
  ELI5 how we should be talking about it?
  - amelius 4y ago
    The main issue is that the explanation should not imply faster-than-light communication.
    - orlp 4y ago
      That isn't implied. A particle pair collapsing from a superposition of to one of its eigenstates upon measurement, is a change in the particle in one location that instantaneously affects the other for all intents and purposes. This still doesn't allow you to use this to transfer information from one point to another faster than light due to the way nature lets you observe and manipulate things (e.g. the no-cloning theorem crucially prevents you from by-passing the permanence of quantum collapse). But the effect is very much real. Much more real than you might think. You can't use it to communicate faster than light, but you absolutely can use it to coordinate faster than light. It's called quantum pseudo-telepathy. See for example the Mermin–Peres magic square game. Two players with two pairs of entangled particles can win this game with 100% probability even if they're lightyears apart, whereas players without this resource can't win 100% of the time if they're separated (e.g. by adding sufficient distance and a time limit to the game).
      - slabity 4y ago
        > This isn't implied. A particle pair collapsing from a superposition of to one of its eigenstates upon measurement, is a change in the particle in one location that instantaneously affects the other for all intents and purposes. If you were to use this explanation to anyone that isn't already deeply familiar with how quantum entanglement works, the "instantaneous" part of it would absolutely imply either FTL communication or at the very least the idea of a hidden variable behind the particles at the point of entanglement. And that's assuming they even understand what an "eigenstate" even is.
colechristensen 4y ago
If enough of these or enough distance between them is achievable, would there be any experiments possible to probe the interactions between general relativity and quantum mechanics? 2m is definitely enough to measure relativistic effects in earths gravity with the most precise atomic clocks we have.
yogenpro 4y ago
Could that be used to measure one-way speed of light? https://en.m.wikipedia.org/wiki/One-way_speed_of_light https://en.m.wikipedia.org/wiki/One-way_speed_of_light
- adgjlsfhk1 4y ago
  No. The standard calculations about the time dilation experienced when moving them apart don't hold without constant speed of light.
heavenlyblue 4y ago
Can anyone explain what is the usual expalnation for what happens when two entangled particles are measured? That is, if one of the particles is measured, and the other is not, what happens to the second one? Is there some time where the second particle is still entangled to the first one or is it going to be entangled until measured?
- bowsamic 4y ago
  > Can anyone explain what is the usual expalnation for what happens when two entangled particles are measured? In the most extreme case of entanglement, the two systems cannot be described separately, but only by some coupled state. I.e., if you have two particles that can be spin up or spin down, you either find them both spin up, or both spin down as an example. That means, if you measure the spin of particle 1 you already know the spin of particle 2. We interpret this as the measurement affecting the other particle instantaneously even though they may be spatially separated. More generally, entanglement just means that there is an extremely strong correlation between the two systems. > That is, if one of the particles is measured, and the other is not, what happens to the second one? Is there some time where the second particle is still entangled to the first one or is it going to be entangled until measured? There is immediately no longer any entanglement after one of the particles is measured. If you measure the same observable again you will get the same result, and if you measure an observable incompatible to that observable on one particle you will not affect the other particle.

168 points by lysp 4y ago

dtx1 4y ago

paywalled. 12ft.io doesnt help.

alexalx666 4y ago
12ft is awesome, thanks!
axiolite 4y ago
Full article: http://webcache.googleusercontent.com/search?hl=en&q=cache%3Ahttps%3A%2F%2Fwww.newscientist.com%2Farticle%2F2337042%2Dtwo%2Datomic%2Dclocks%2Dhave%2Dbeen%2Dquantum%2Dentangled%2Dfor%2Dthe%2Dfirst%2Dtime%2F http://webcache.googleusercontent.com/search?hl=en&q=cache%3...

kalupa 4y ago

https://archive.ph/VVwbl https://archive.ph/VVwbl EDIT: ah, dang, also doesn't work

colejohnson66 4y ago

From /r/science[0]: https://news.mit.edu/2020/atomic-clock-time-precise-1216 https://news.mit.edu/2020/atomic-clock-time-precise-1216 [0]: https://old.reddit.com/r/science/comments/x8khxg/two_atomic_clocks_have_been_quantum_entangled_for/injginb/?context=3 https://old.reddit.com/r/science/comments/x8khxg/two_atomic_...

rolph 4y ago

MIT news: https://news.mit.edu/2020/atomic-clock-time-precise-1216 https://news.mit.edu/2020/atomic-clock-time-precise-1216 seems to be the better link, also reveals subject is a 2020 discovery, was also published in Nature: https://www.nature.com/articles/s41586-022-05088-z https://www.nature.com/articles/s41586-022-05088-z [paywall] "Abstract Optical atomic clocks are our most precise tools to measure time and frequency1,2,3. Precision frequency comparisons between clocks in separate locations enable one to probe the space–time variation of fundamental constants4,5 and the properties of dark matter6,7, to perform geodesy8,9,10 and to evaluate systematic clock shifts. Measurements on independent systems are limited by the standard quantum limit; measurements on entangled systems can surpass the standard quantum limit to reach the ultimate precision allowed by quantum theory—the Heisenberg limit. Although local entangling operations have demonstrated this enhancement at microscopic distances11,12,13,14,15,16, comparisons between remote atomic clocks require the rapid generation of high-fidelity entanglement between systems that have no intrinsic interactions. Here we report the use of a photonic link17,18 to entangle two 88Sr+ ions separated by a macroscopic distance19 (approximately 2 m) to demonstrate an elementary quantum network of entangled optical clocks. For frequency comparisons between the ions, we find that entanglement reduces the measurement uncertainty by nearly \(\sqrt{2}\), the value predicted for the Heisenberg limit. Today’s optical clocks are typically limited by dephasing of the probe laser20; in this regime, we find that entanglement yields a factor of 2 reduction in the measurement uncertainty compared with conventional correlation spectroscopy techniques20,21,22. We demonstrate this enhancement for the measurement of a frequency shift applied to one of the clocks. This two-node network could be extended to additional nodes23, to other species of trapped particles or—through local operations—to larger entangled systems. "

clouddrover 4y ago
The New Scientist article is talking about network of two entangled optical atomic clocks, which is a step beyond entanglement within one clock. Here's what Oxford's physics department says about it: https://www.physics.ox.ac.uk/news/quantum-network-entangled-atomic-clocks https://www.physics.ox.ac.uk/news/quantum-network-entangled-...

amelius 4y ago

> Two atomic clocks have been connected using quantum entanglement – a property that intrinsically links them so that changes in one instantaneously affect the other. Not this explanation again ...

rco8786 4y ago
ELI5 how we should be talking about it?
- amelius 4y ago
  The main issue is that the explanation should not imply faster-than-light communication.
  - orlp 4y ago
    That isn't implied. A particle pair collapsing from a superposition of to one of its eigenstates upon measurement, is a change in the particle in one location that instantaneously affects the other for all intents and purposes. This still doesn't allow you to use this to transfer information from one point to another faster than light due to the way nature lets you observe and manipulate things (e.g. the no-cloning theorem crucially prevents you from by-passing the permanence of quantum collapse). But the effect is very much real. Much more real than you might think. You can't use it to communicate faster than light, but you absolutely can use it to coordinate faster than light. It's called quantum pseudo-telepathy. See for example the Mermin–Peres magic square game. Two players with two pairs of entangled particles can win this game with 100% probability even if they're lightyears apart, whereas players without this resource can't win 100% of the time if they're separated (e.g. by adding sufficient distance and a time limit to the game).
    - slabity 4y ago
      > This isn't implied. A particle pair collapsing from a superposition of to one of its eigenstates upon measurement, is a change in the particle in one location that instantaneously affects the other for all intents and purposes. If you were to use this explanation to anyone that isn't already deeply familiar with how quantum entanglement works, the "instantaneous" part of it would absolutely imply either FTL communication or at the very least the idea of a hidden variable behind the particles at the point of entanglement. And that's assuming they even understand what an "eigenstate" even is.

colechristensen 4y ago

If enough of these or enough distance between them is achievable, would there be any experiments possible to probe the interactions between general relativity and quantum mechanics? 2m is definitely enough to measure relativistic effects in earths gravity with the most precise atomic clocks we have.

yogenpro 4y ago

Could that be used to measure one-way speed of light? https://en.m.wikipedia.org/wiki/One-way_speed_of_light https://en.m.wikipedia.org/wiki/One-way_speed_of_light

adgjlsfhk1 4y ago
No. The standard calculations about the time dilation experienced when moving them apart don't hold without constant speed of light.

heavenlyblue 4y ago

Can anyone explain what is the usual expalnation for what happens when two entangled particles are measured? That is, if one of the particles is measured, and the other is not, what happens to the second one? Is there some time where the second particle is still entangled to the first one or is it going to be entangled until measured?

bowsamic 4y ago
> Can anyone explain what is the usual expalnation for what happens when two entangled particles are measured? In the most extreme case of entanglement, the two systems cannot be described separately, but only by some coupled state. I.e., if you have two particles that can be spin up or spin down, you either find them both spin up, or both spin down as an example. That means, if you measure the spin of particle 1 you already know the spin of particle 2. We interpret this as the measurement affecting the other particle instantaneously even though they may be spatially separated. More generally, entanglement just means that there is an extremely strong correlation between the two systems. > That is, if one of the particles is measured, and the other is not, what happens to the second one? Is there some time where the second particle is still entangled to the first one or is it going to be entangled until measured? There is immediately no longer any entanglement after one of the particles is measured. If you measure the same observable again you will get the same result, and if you measure an observable incompatible to that observable on one particle you will not affect the other particle.