5 ms·

Paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.150202 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.13... > We construct a me

Paper: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.131.150202 https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.13... > We construct a metrology experiment in which the metrologist can sometimes amend the input state by simulating a closed timelike curve, a worldline that travels backward in time. The existence of closed timelike curves is hypothetical. Nevertheless, they can be simulated probabilistically by quantum-teleportation circuits. We leverage such simulations to pinpoint a counterintuitive nonclassical advantage achievable with entanglement. Our experiment echoes a common information-processing task: A metrologist must prepare probes to input into an unknown quantum interaction. The goal is to infer as much information per probe as possible. If the input is optimal, the information gained per probe can exceed any value achievable classically. The problem is that, only after the interaction does the metrologist learn which input would have been optimal. The metrologist can attempt to change the input by effectively teleporting the optimal input back in time, via entanglement manipulation. The effective time travel sometimes fails but ensures that, summed over trials, the metrologist’s winnings are positive. Our Gedankenexperiment demonstrates that entanglement can generate operational advantages forbidden in classical chronology-respecting theories.

pama 3y ago
There is a nice explanation at the end of the letter: “While PCTC simulations do not allow you to go back and alter your past, they do allow you to create a better tomorrow by fixing yesterday’s problems today.”
- DaveSchmindel 3y ago
  Interesting. Isn't that just problem solving? If yesterday's problems are unsolved by today, aren't they just today's problems?
  - gerad 3y ago
    I read it as: - Today, I need to predict tomorrow’s weather. - Yesterday I made some measurements of the (temperature, pressure, etc) conditions that I need for today’s prediction. - Yesterday it was impossible to know what measurements I’d optimally need to take for today’s forecast. - Today, I can (quantumly, probabilisticly) go back in time and make sure I have the optimal set of measurements for today’s prediction. - I can’t change anything that happened between yesterday and today, but I now have better information I can use to change tomorrow.
    - goodluckchuck 3y ago
      So you can measure the past, but not change it?
    - xwdv 3y ago
      If you already know the optimal set of measurements why not skip the whole traveling back in time part and just change tomorrow today?
      - gerad 3y ago
        > The problem is that, only after the interaction does the metrologist learn which input would have been optimal.
- dvaletin 3y ago
  Basically, having infinite budget you can send any gift you can imagine to your friend via Amazon at day-1 and cancel irrelevant orders at day-0 except correct one to make your friend happy at his BD, which is day+1. Make better future correcting your past decisions based on today information. Now the question is: how to get enough money?
chrisweekly 3y ago
"Our Gedankenexperiment demonstrates that..." "Gedankenexperiment" sounds an awful lot like "thought experiment".
- kadoban 3y ago
  That's the translation, yeah. They're a very important tool in physics for exploring the consequences of known or hypothsized physical principles.
- mdekkers 3y ago
  That’s literally what it means, and it’s a minor nitpick I have - it’s an English paper, just use English. Using the German word here just increases noise.
  - galaxyLogic 3y ago
    I think it comes from Einstein whose Gedanken Experiments lead to the discovery of relativity. Einstein came from a German-speaking country. So what the authors are saying is "We're basically doing a similar thing as Einstein did". Jargon is to be avoided but this is more like a tribute to the great physicist Einstein.
    - dr_kiszonka 3y ago
      A less charitable interpretation would be that is a form of self-aggrandizement.
      - 77pt77 3y ago
        It's both.
      - euroderf 3y ago
        Sort of like wrapping yourself in the flag. Of Einstein.
      - corney91 3y ago
MrRolleyes 3y ago
[dead]

pama 3y ago

There is a nice explanation at the end of the letter: “While PCTC simulations do not allow you to go back and alter your past, they do allow you to create a better tomorrow by fixing yesterday’s problems today.”

DaveSchmindel 3y ago
Interesting. Isn't that just problem solving? If yesterday's problems are unsolved by today, aren't they just today's problems?
- gerad 3y ago
  I read it as: - Today, I need to predict tomorrow’s weather. - Yesterday I made some measurements of the (temperature, pressure, etc) conditions that I need for today’s prediction. - Yesterday it was impossible to know what measurements I’d optimally need to take for today’s forecast. - Today, I can (quantumly, probabilisticly) go back in time and make sure I have the optimal set of measurements for today’s prediction. - I can’t change anything that happened between yesterday and today, but I now have better information I can use to change tomorrow.
  - goodluckchuck 3y ago
    So you can measure the past, but not change it?
  - xwdv 3y ago
    If you already know the optimal set of measurements why not skip the whole traveling back in time part and just change tomorrow today?
    - gerad 3y ago
      > The problem is that, only after the interaction does the metrologist learn which input would have been optimal.
dvaletin 3y ago
Basically, having infinite budget you can send any gift you can imagine to your friend via Amazon at day-1 and cancel irrelevant orders at day-0 except correct one to make your friend happy at his BD, which is day+1. Make better future correcting your past decisions based on today information. Now the question is: how to get enough money?

chrisweekly 3y ago

"Our Gedankenexperiment demonstrates that..." "Gedankenexperiment" sounds an awful lot like "thought experiment".

kadoban 3y ago
That's the translation, yeah. They're a very important tool in physics for exploring the consequences of known or hypothsized physical principles.
mdekkers 3y ago
That’s literally what it means, and it’s a minor nitpick I have - it’s an English paper, just use English. Using the German word here just increases noise.
- galaxyLogic 3y ago
  I think it comes from Einstein whose Gedanken Experiments lead to the discovery of relativity. Einstein came from a German-speaking country. So what the authors are saying is "We're basically doing a similar thing as Einstein did". Jargon is to be avoided but this is more like a tribute to the great physicist Einstein.
  - dr_kiszonka 3y ago
    A less charitable interpretation would be that is a form of self-aggrandizement.
    - 77pt77 3y ago
      It's both.
    - euroderf 3y ago
      Sort of like wrapping yourself in the flag. Of Einstein.
    - corney91 3y ago

MrRolleyes 3y ago

[dead]