# Elitzur–Vaidman Bomb-Tester Extension for Boolean Variable Return

• viralplatipus
In summary: I'm not sure, I'm just trying to get my ideas out there and see what people think. In summary, this person's idea is flawed because it doesn't have a way to detect the photon at B without collapsing the wave-function and it also has a design flaw where the internal tester's photon could be detected.
viralplatipus
Hey everyone, I'm new to the forums so sorry if I'm making a post that's obviously ridiculous but my level of understanding only takes me so far, hence the need to post here.

I just finished my bachelor of science degree in Biochemistry this summer but only have an A-level qualification in physics so I'm hoping someone could add some insight into an idea I was putting together.

So yesterday I discovered the Elitzur-Vaidman bomb-tester (17 years behind the game I know) and thought it was an incredible idea that you could observe something without actually having observed it (or I guess observed it in a parallel world) but thought it might be able to go further than just being able to detect the presence of something without observation and actually return information from whatever process that technically hasn't happened in our reality.

Obviously it's a long shot and I'm sceptical about this even being possible, and I know I'm not the first to think along these lines. None the less I spent the last day coming up with a design based on the original EV bomb-tester but adding another tester within itself, I'm pretty sure it's flawed but thought I'd share it and would love to hear some feedback.

If you look at the diagram I have attached I will do my best to describe what I was thinking:

So the main diagram with the brown lines represents an EV bomb-tester like the diagram found here: http://en.wikipedia.org/wiki/Elitzur–Vaidman_bomb-tester

Normally when a photon reaches B it would cause collapse of the wave-function and so either end the path right there or prevent constructive coherence at the end half-silvered mirror if the photon was along the top arm (depending on where it 'decided' to be) and allow a 50% chance of hitting the otherwise un-reachable C detector.

So I thought if you could have a sensor at B which activated some process upon reception of the photon and then either prevented or allowed the photon to reach the end mirror dependant on the outcome of the process you could essentially measure the outcome of that process 50% of the time without it have ever being run.

The problem with that is there would be no way to sense the photon at B without collapsing the wave-function. But then I thought the whole objective of the EV bomb-tester was to be able to counterfactually identify the presence of a particle, which would avoid collapsing the wave-function.

So based on that principle I added a second EV bomb-tester, where the B's of both testers would intersect. This is the point where it's kind of flawed... I'm thinking at this intersection both photons will be wave-functions and I don't know what happens when the potential (super)positions of photons collide with each other, I assume either nothing happens and both continue on their path, in which case my design is useless or they observe each other and are forced to determine a position on either of their relative bomb-tester's arms. In which case my design is also not going to work. But if it could somehow cause an observation on the internal bomb-tester's photon, while leaving the main tester's photon un-observed (this probably isn't possible, and so is the reason no one has done this... unless maybe it could be possible if the photons had different energy levels or something, I'm clutching at straws here) then I guess independent of which arm the internal tester's photon decided upon it would either have a 25% chance of registering at Cx or there would be a 50% chance of no detection which could be linked to a time-limit device that could activate E as Cx also would.

E would be the process that run, maybe for a simple example some very quick pre-determinable computer calculation and based on a boolean output would decide to either obstruct or clear the path of the main photon at F before it reached there, which I understand would mean both arms of the main tester would need to be long enough to keep a photon on either arm traveling long enough for the calculation and the result at F, maybe keeping the photon in a smaller area during this time with mirrors if that's possible. But then the result could be obtained by the blocking of the main photon at F.

So if the machine was run, and photon observed by the internal tester which then had a 75% chance of running it's process and blocking the photon's path at F (dependant on process' output). 25% of the time the machine is run, it would have a 75% chance of processing an output and we could only be certain of the output when a photon is blocked rather than allowed through, as it would be detected in C, which probably wouldn't be that great or useful to us... BUT... would have just calculated the output to a process that technically never ran in reality.

So if it IS possible, and obviously would mean drastic alterations to my diagram I'm sure or maybe some whole other way of doing it.. but it would prove we've essentially obtained information out of nothing, which would be very exciting indeed. :)

Anyway, it was just an idea I wanted to throw out there, would love to hear some expert knowledge on why it most probably isn't at all possible or what you think of my first attempt at theoretical physics!

#### Attachments

• evbombviral.gif
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Your basic idea is that you want to determine the outcome of a process without actually running the process. Is that correct? E is some sort of logic circuit?

interesting idea, but I don't think your detecting light with light method is going to work though.

I think you will keep running into the following problem...
You can't know the photon took the bottom path without loosing interference. Or in other words the sensor would always act like the bomb.

Yeah.. that's why I was trying to use a second bomb-tester, so the sensor would essentially be the top arm of that sensor (sensing that the bottom arm has been hit with a photon, but it didn't actually hit it) but I know that's flawed because I'm supposedly using the potential position of a photon to sense the potential position of another photon.

## 1. What is the Elitzur-Vaidman Bomb-Tester Extension for Boolean Variable Return?

The Elitzur-Vaidman Bomb-Tester Extension for Boolean Variable Return is a thought experiment proposed by physicists Avshalom C. Elitzur and Lev Vaidman in 1993. It is an extension of the original Elitzur-Vaidman bomb-testing problem, which is used to demonstrate the principles of quantum mechanics.

## 2. How does the Elitzur-Vaidman Bomb-Tester Extension work?

In the Elitzur-Vaidman Bomb-Tester Extension, a Boolean variable (a variable with only two possible values, true or false) is added to the original bomb-testing scenario. This variable represents whether or not the bomb has exploded. By measuring the quantum state of the bomb, the experimenter can determine both whether the bomb has exploded and the value of the Boolean variable.

## 3. What is the significance of the Elitzur-Vaidman Bomb-Tester Extension?

The Elitzur-Vaidman Bomb-Tester Extension is significant because it demonstrates the concept of quantum superposition, where a particle can exist in multiple states simultaneously. It also highlights the counterintuitive nature of quantum mechanics, where measuring a particle can change its state.

## 4. How is the Elitzur-Vaidman Bomb-Tester Extension related to quantum computing?

The Elitzur-Vaidman Bomb-Tester Extension is often used as an example in discussions about quantum computing because it demonstrates the power of quantum effects in information processing. It also highlights the potential for using quantum superposition to perform multiple computations simultaneously.

## 5. Is the Elitzur-Vaidman Bomb-Tester Extension a practical experiment or just a theoretical concept?

The Elitzur-Vaidman Bomb-Tester Extension is currently just a theoretical concept, as it requires precise control and measurement of quantum systems. However, it has been the subject of ongoing research and could potentially have practical applications in the future, particularly in the field of quantum computing.

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