# How long does it take to detect entanglement?

• B
• platosuniverse
In summary, it takes a few minutes, hours or days to measure the entanglement between particles. Once the entanglement is detected, it can take as long as 30 hours for the results to be compared.

#### platosuniverse

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

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).

## 1. How is entanglement detected?

Entanglement is detected through the use of quantum measurements, specifically Bell tests, which compare the states of two or more particles.

## 2. How long does it take to detect entanglement?

The time it takes to detect entanglement depends on the experimental setup and the complexity of the system being observed. In some cases, entanglement can be detected instantaneously, while in others it may take hours or even days.

## 3. What factors affect the speed of detecting entanglement?

The speed of detecting entanglement can be affected by various factors such as the distance between the entangled particles, the accuracy of the measurement devices, and any external noise or interference in the system.

## 4. Can entanglement be detected in real-time?

Yes, entanglement can be detected in real-time using advanced measurement techniques and high-speed data processing. However, the complexity of the system being observed may affect the speed of detection.

## 5. Is there a limit to how quickly entanglement can be detected?

There is currently no known limit to how quickly entanglement can be detected. With advancements in technology and experimental techniques, it is possible that entanglement detection could become even faster in the future.