# Random Museings on quantum computeing.

1. May 25, 2006

### Xira

Hi. I am just a biologist with an intrest in theoretical physics. Please, jump up and down on my wrongness:) This is the gist of a conversation on the subject of a holo stealth feild that was never replied to in a games forum for a game I played at one point.

Essentially the question is "Is a solidstate quantum detector in a nearly closed system capable of detecting?"

Thats not technically correct, but yes, a quantum computer would fix the delay problem.

Quantum computers can in this case calculate the probability of photon intensity, giving the probable image the minute it is detected. The only delay in the system would be how fast the sensors can detect photons and how fast the holographic emiters can generate them.

Dam was hopeing nobody would catch that I just pulled that out of thin air:)

Am a geneticist, not a quantum physicist!

If you actually understand this stuff, I have some more questions for you. Essentially as I (Actually not made up) understand it such a system would calculate the photon's probale location at area X if it has come in through photon detector Y because it could have passed through the object with whatever irrelivantly small probability.

Which is to say that by observeing the diffrence in the result matrix of what is actually and what could have been had the photon from detector Y passed through the entire object it can in zero time generate the result.....

Subject to non quantum systems lag:)

Which brings up an intresting phenonomom......

You could in theory place the photon detector inside the object, and still recive the same result as you could detect the diffrence between the result of what the system would have generated had the photon tunneled through the object to the point of the detector and then triggered the detector, and the result had the photon tunneled entirly through the object.

Which leads me to belive that the whole system could be simplified by haveing 2 layers of photon detectors and 2 quantum calculations then compareing the probailistic results matrix between them via a 3rd quantum calculation. Reciveing the vector of the photons enableing a true holographic simulation to be put into place around the vehicle.

Thus entirly negateing the photon detector lag, as you would only need the detectors to be able to detect the image with whatever infinitly small probalitity, NOT to actually detect anything. your new system would only be susceptiable to holographic generator lag.

Which leads me to wonder why they don't use quantum detectors in this manner to detect for the existance of superrare or superneutral particles in high energy particle physics.

All that would be nessicary is for the system to be ABLE to detect such a particle, not to actually detect it. And for such a particle to EXIST. If it could not exist(I.E. a make belive particle), and your detector was actually capable of detecting it, then you would be able to tell. If it did exist and your detector was able to detect it then it would by definition detect it due to the laws of quantum dynamics......

Could entirly take the whole high energy generator expensivness of the current experimentation out of it....

Last edited: May 25, 2006
2. May 25, 2006

### Xira

Well as my cut and paste from the other forums didn't seem to come over so well, I'll give the long summary:)

You have a quantum computer and a standard photon detector in a nearly closed system. I.E. the only way into the system is via tunneling. A photon incident upon the photon detector is blocked entry to the system, but could have tunneled through with some small probability. The quantum computer should be able to detect the diffrence in probability because it could have run.

IRL You have a quantum computer and a photon detector in a block of solid cement a mile thick. Can the computer generate an image of 'outside'.

3. May 26, 2006

Hi, I don't think a photon can "tunnel" through a barrier in the conventional sense. Mathematically speaking, you cannot write the wavefunction for a photon as it is not localized. (There are other problems as well.)

This brings us to the question if any exchange particle can tunnel at all? If you are thinking about the nutrino detection experiments under the earth, a) I have not heard of any results come off that and b) the earth is transparent to the nutrino, hence tunneling does not come into the picture.

I'm not sure I understand your question correctly (sorry, maybe I'm just dumb!) What do you mean by a closed system? Is it one which is decoupled from the envoirnment?

If you are looking for the quantum mechanical description of a photo-detector, look up the papers of L.Mandel, the greatest modern day physcist/father of quantum optics. Unfortunately, the scientific community lost him to illness.

4. May 26, 2006

Well, allow me to formulate the problem in another way and tell me if it is what you had in mind.

We have a cavity completely decoupled from the envoirnment. There are only two photons in the universe, one outside the cavity and one inside. There is a detector inside the cavity. The detector registers a click when a photon is detected.

You are asking me what is the probability of the click registered being due to the photon from outside the cavity?

Well, this is only possible if the cavity absorbs the photon from outside and re-emitting it inside. In taht case the cavity is NOT an isolated cavity and our initial supposition is wrong.

In this case, you have to write the wavefunction of the entire system, i.e photon outside, photon inside, cavity, detector and the vacuum modes inside, vacumm modes outside. Once you have this wavefunction, all you do is take the expectation value (probability) using the operator which describes the wavefunction of the detector.

So you see that there is an essential conflict between how your problem is set up. :)

5. May 26, 2006

### CarlB

This is what I was taught, too, but it seems that if you look at helicity wave states, you can do it. I've seen this in a number of places, but I can't recall where first I've seen it. But for example:

http://www.cft.edu.pl/~birula/publ/APPPwf.pdf

Carl

6. May 26, 2006