How long does it take to detect entanglement?

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Discussion Overview

The discussion revolves around the time required to detect entanglement in quantum experiments, exploring various factors that influence this duration, including the speed of electronics and the nature of measurements. Participants share their insights and experiences related to entanglement experiments, focusing on the correlation of measurement results and the implications of timing in these processes.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant inquires about the duration it takes to determine if particles are entangled, suggesting a range from minutes to days.
  • Another participant states that detection speed is limited by the electronics and signal propagation, typically in the nanosecond range for standard setups.
  • A participant questions whether one can infer entanglement after measurements are taken but before results are compared, raising concerns about the implications of not comparing results.
  • Another participant agrees that results can be correlated once compared, indicating that correlation can be calculated from the measurement results.
  • Some participants express surprise at the speed of detection, initially expecting it to take longer, such as hours.
  • A later contribution mentions that the current record for measuring entanglement involves a significant amount of time (30 hours) to gather enough statistics for reliable results, while noting that simpler cases may allow for quicker measurements.

Areas of Agreement / Disagreement

Participants generally agree that detection can occur rapidly, in the nanosecond range, but there is no consensus on the implications of timing and correlation assumptions. The discussion includes differing views on the necessity of comparing results to infer entanglement.

Contextual Notes

Limitations include the dependence on experimental setup specifics, the nature of the measurements taken, and the statistical requirements for establishing entanglement beyond reasonable doubt. The discussion also highlights the complexity of measuring different types of entangled states, which may affect timing.

platosuniverse
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I was just curious. Does it take a few minutes, hours or days? Has anyone here carried out an entanglement experiment? From what I understand, the results of the measurement of entangled particles go to a coincidence counter and that's where they check the results. How long is the period before they know the particles are correlated?

Thanks
 
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As fast as your electronics is, or as fast as your signal can propagate in the cables (limited by the speed of light) - nanoseconds for typical setup sizes.
 
Can one INFER that the particles were entangled at a point in time AFTER Bob and Alice made the made the measurements , but BEFORE they were compared by ALICE and Bob or anybody for that matter.

The way I see it, IF they are never compared , there is no way of knowing, so no argument can be made.

But If they are compared some time after they were recorded , why can we not ASSUME/INFER that they were correlated just after the point in time of the last measurement.

If we cannot assume this , what is the reason ??

I know Bell's inequality shows that the particles could not have initial hidden variable(s) , when created , but I'm more interested in the time between
the last measurement taken and the data compared.
 
Johan0001 said:
But If they are compared some time after they were recorded , why can we not ASSUME/INFER that they were correlated just after the point in time of the last measurement.
Of course we can do that. When we compare the results we know the measurement results. We can calculate the correlation.
 
mfb said:
As fast as your electronics is, or as fast as your signal can propagate in the cables (limited by the speed of light) - nanoseconds for typical setup sizes.

Really, that's fast. I thought it would take a lot longer like a few hours. Thanks for the info.
 
What do you expect to happen in these hours?
 
mfb said:
What do you expect to happen in these hours?

I honestly had no idea. I just thought it would take more time to compare the results but I can see why this would happen in nanoseconds.
 
platosuniverse said:
I was just curious. Does it take a few minutes, hours or days? Has anyone here carried out an entanglement experiment? From what I understand, the results of the measurement of entangled particles go to a coincidence counter and that's where they check the results. How long is the period before they know the particles are correlated?

Thanks
The current record of 7.1 ebits worth of entanglement per particle pair took about 30 hours or so to measure :)
https://arxiv.org/abs/1804.04515
Detectors may be fast, but you need enough statistics from many detection events to show there is entanglement beyond reasonable doubt.

That said, some systems may be way faster, if all you want to do is witness that there is entanglement instead of knowing how much there is. The simple case of the polarization of an entangled pair of photons can be measured much more quickly, because there's a lot fewer total outcomes to the entire probability distribution, so the statistics fill out a lot faster than the position-momentum statistics measured in this paper, which have many more possible outcomes (to put it mildly).
 

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