Tesseract Posted May 26, 2004 Author Posted May 26, 2004 have you read ANY of the above posts??? I mean REALLY read then properly and understood them? All you said is if I heard of a beam splitter?whats that?can it separate photons?
YT2095 Posted May 26, 2004 Posted May 26, 2004 yes it can, a beam splitter is a simple peice of optics, it`s a partial mirror, you can see through it but it`s also reflective. they use them in CD players and laser printers basicly you`ll have that splitter at 45 degrees fire your laser at it, some light will pass through some will be reflected at 90 degrees, straight away you`ve halved the amount of photons from there you can use the interferance patern slits and fractionalise them even further. it doesn`t take muck working out to know that eventualy you can easily generate a single stream when you consider that a continuos beam laser isn`t used but a pulsed laser with a limited emission time, there`s also crystals that can be used that pass only a fraction of a second of light before switch off. all these combined are more than effective as producing this effect a reasonable effect can even be done at home with regular junk from a scrap yard and a 5 dollar pen laser
Tesseract Posted May 26, 2004 Author Posted May 26, 2004 Eventually wouldnt you just have a beam of 1 photon thick light?
YT2095 Posted May 26, 2004 Posted May 26, 2004 in some instances yes, in other laser bursts there would be non that made it through. rem, it`s a PULSED laser in use and not a continuos beam type the distances for switch crystals are critical also, allowing a switch time that will aproach a percentage of light speed to managable levels
Tesseract Posted May 26, 2004 Author Posted May 26, 2004 There are two reasons why the experiment in this thread is impossible: 1)Statistiaclly its impossible to measure out or have one photon, you can never do it even wiht a beam splitter you would have less and less accuracy as the amount of photons became less, it would be unmeasureable. 2)You could never make a 100% secure device (for the experiment) that didnt let in any radiation or particles or light from the outside and you could never have a 100% flat mirror that would reflect the photons exactly back because the photons are smaller that the atoms in the mirror.Also you couldnt have a device to constantly see the photon in the chamber everytime it would hit something (its moving always at light speed) it would lose energy until it disappears. So how would you do it?
swansont Posted May 26, 2004 Posted May 26, 2004 I dont see how anyone is able to remove a photon from light' date=' its half wave and half particle.. Even if so the experiment wouldnt work, the photon wouldnt stay in the right place, you couldnt even see where it is.You would need a 100% dark space to do this.So that no other photons can enter.And the mirrors would have to be 100% straight as to not bounce the photon somewhere else.How can you measure something thats moving at the speed of light?[/quote'] You would use curved mirrors. You are correct in thinking that flat mirrors don't make a stable cavity, but stable cavity designs do exist. They just don't use flat mirrors.
swansont Posted May 26, 2004 Posted May 26, 2004 yes it can' date=' a beam splitter is a simple peice of optics, it`s a partial mirror, you can see through it but it`s also reflective. they use them in CD players and laser printers [/quote'] They aren't half-silvered like most bathroom-type mirrors. Good optical beam splitters are often two prisms glued together, with the proper indices of refraction to split off the desired fraction of the incident light. Or to reflect one polarization while letting the other orientation to be transmitted - you can then control the ratio with a wave plate, if the incident light is already polarized.
Tesseract Posted May 26, 2004 Author Posted May 26, 2004 You would use curved mirrors. You are correct in thinking that flat mirrors don't make a stable cavity, but stable cavity designs do exist. They just don't use flat mirrors. Its not about the curvature of the mirror its about the curvature of the surface of the mirror (there isnt a perfectly flat mirror) .Besides there is not 100% reflective surface in existense the photon would be absorbed on the second or third bounce...
Tesseract Posted May 26, 2004 Author Posted May 26, 2004 They aren't half-silvered like most bathroom-type mirrors. Good optical beam splitters are often two prisms glued together, with the proper indices of refraction to split off the desired fraction of the incident light. Or to reflect one polarization while letting the other orientation to be transmitted - you can then control the ratio with a wave plate, if the incident light is already polarized. It dosnt matter what the beam splitter is the problem is that it cant separate a single photon from the source.Thus the experiment is impossible.
swansont Posted May 26, 2004 Posted May 26, 2004 There are two reasons why the experiment in this thread is impossible: 1)Statistiaclly its impossible to measure out or have one photon' date=' you can never do it even wiht a beam splitter you would have less and less accuracy as the amount of photons became less, it would be unmeasureable. 2)You could never make a 100% secure device (for the experiment) that didnt let in any radiation or particles or light from the outside and you could never have a 100% flat mirror that would reflect the photons exactly back because the photons are smaller that the atoms in the mirror.Also you couldnt have a device to constantly see the photon in the chamber everytime it would hit something (its moving always at light speed) it would lose energy until it disappears. So how would you do it? [/quote'] It's been done, so all of this is crap. In cavity QED a single photon in a high-finesse cavity has very profound effects. You can tell if the cavity has a photon in it or not. So not only is it possible, but they were doing it 10 years ago and have moved on.
Tesseract Posted May 26, 2004 Author Posted May 26, 2004 It's been done' date=' so all of this is crap. In cavity QED a single photon in a high-finesse cavity has very profound effects. You can tell if the cavity has a photon in it or not. So not only is it possible, but they were doing it 10 years ago and have moved on.[/quote'] Your very credible swansont.
kjitta Posted May 27, 2004 Posted May 27, 2004 I can contribute something on single photon issue in this thread. It is possible to seperate single photons from many, it is used in quantum cryptography as one example. but there is one catch, you are never able to say for sure that your pulse containy 1 and only 1 photon. The common method is to use a pulsed laser and attenuate it so much that each pulse contains on average only .01 photons. In this casse you have a train of pulses of which many pulses will be empty, but some of them will contain only a single photon. There is also a chance that some pulses have more (poissonian statistics if you want to look it up) but you limit the chance of that happening by chosing a low average photon number per pulse as said. Single photon sources are still some time away but they are in development. A group at the neighbouring university I know are working on these and we aim to characterise them over a 67 km fiber link within a few years. As for trapping a single photon in a cavity. It is possible, but dont think of it as a one of experiment. you would have to carry out thousands and build up a statistical picture of what you wish to characterise.
Tesseract Posted May 27, 2004 Author Posted May 27, 2004 The problem again is how are you going to launch the photon so it hits the mirrors and how to make it a 100% reflective surface?As I sadi the photon would be absorbed in 1-2 bounces.
kjitta Posted May 27, 2004 Posted May 27, 2004 As I said, don't think of it of a one of hit or miss experiment. you can make a cavity with one mirror as close to 100% reflective as possible, the second say 98%. If you have a train of pulses prepared so that single photons arrive at the cavity every minute, say. statistically 2 in every 100 potons will enter the cavity and bounce back and forth with a certain average life time of which it will continue bouncing back and forth before it is destroy by some mean or it is transmitted by one of the mirrors. The bottom line is, it is possible to prepare a cavity with a single photon within it and the photon will have a certain life time in the cavity before it is absorbed (as you were saying) or it is transmitted through a mirror. It is just as with an excited atom. It will decay again at some average time after the excitation, but you will find if you repeat the experiment that some excited atoms stay excited much longer than most.
swansont Posted May 27, 2004 Posted May 27, 2004 Your very credible swansont. Given your other responses I have to assume this is sarcasm. Also unable to use Google very well.
swansont Posted May 27, 2004 Posted May 27, 2004 Its not about the curvature of the mirror its about the curvature of the surface of the mirror (there isnt a perfectly flat mirror) .Besides there is not 100% reflective surface in existense the photon would be absorbed on the second or third bounce... Here is a link to a CalTech group doing cavity QED. Note the 0.9999984 reflectivity of their mirrors. Photons will bounce more than 2 or 3 times. Here is a Stanford group. Note the link to the "Quantum Dot Turnstile" and one of the refernces: "An efficient source of single photons: a single quantum dot in a micropost microcavity" Hint: "single" isn't referring to its marital status
Tesseract Posted May 27, 2004 Author Posted May 27, 2004 Here is a link to a CalTech group doing cavity QED. Note the 0.9999984 reflectivity of their mirrors. Photons will bounce more than 2 or 3 times. Here is a Stanford group. Note the link to the "Quantum Dot Turnstile" and one of the refernces: "An efficient source of single photons: a single quantum dot in a micropost microcavity" Hint: "single" isn't referring to its marital status About the first one: "it has been possible for the first time to trap single atoms with a single-photon strength laser field. " single photon strength not a single photon ,I already said a single photon laser was possible.And also: "Pictured is part of this experiment - a cesium MOT dropping onto a high-finesse cavity" it dosnt say its a photon??? "Far off-resonant traps: a tool for confining atoms in cavities " The experiment was to trap an atom in a cavity not to bpunce a single photon in an enclosed space to measure how long it took to get to the mirror. ----------------------------------------------------------------------- "An efficient source of single photons is thus in demand. A single photon turnstile device is such a source. On this page you can read about recent experimental demonstration of a single photon turnstile device in our group. You may also check out more pictures from a recent talk about this device" "The current that flows in this situation was measured to be locked to integer multiples of the modulation frequency. This gives further evidence for regulated single photon emission." "Evidence", "experimenta"l, "thus in demand"....it dosnt look very convincing?
swansont Posted May 28, 2004 Posted May 28, 2004 OK Tess. Pick these apart. I gave you the first two. There's only about 1900 more to go.
Tesseract Posted May 28, 2004 Author Posted May 28, 2004 OK, swansont will you read these yourselves and explain how this has to do with single photon. a beam of single photon pulses (as in one link) does not = a single photon I dont want to discuss this stupid experiment anymore its geting boring.
Sayonara Posted May 28, 2004 Posted May 28, 2004 a beam of single photon pulses (as in one link) does not = a single photon Ever seen a tennis player using one of those ball launcher thingies? Find one and ask them them if they consider the balls to be single entities or a steady stream, and if they therefore treat them differently.
kjitta Posted May 28, 2004 Posted May 28, 2004 Cummon Tess, are you suffering from a mental block or do you just refuse to lissen to what I and others are trying to explain to you. 1) It is possible possible to single out single photons with certain limitations but nothing that can't be described by some basic statistics. We do this in quantum cryptography all the time, and it works. Hell we can now even teleport the quantum state of a single photon onto an other photon. You might want to check your sources becasue experiments on the single photon level has matured a lot lately. 2) mirrors reflect single photons more than 1-2 times, no question about it. As I tried to point out some will reflecte many times some not even ones. A photon will have a mean lifetime in the cavity, and it can be calculated. This is simple, just think about how a laser operates. Many photons are traped in a cavity and undergo gain as they pass through the gain medium. Each photon undergo an average number of cavity roundtrips before they excit. Given this, what makes you think it is different with a single photon. Why sohuld it only experience 1 or two roundtrips in the cavity? 3) a photon moves 30 cm every 1 ns make the cavity long enough and time of flight between two mirrors will be several ns giving you enough time to move a mirror. It can be done.
swansont Posted May 28, 2004 Posted May 28, 2004 OK' date=' swansont will you read these yourselves and explain how this has to do with single photon.a beam of single photon pulses (as in one link) does not = a single photon I dont want to discuss this stupid experiment anymore its geting boring.[/quote'] And this would be your professional opinion, that I should take over all of the textbooks and journal articles I've read, and lectures and discussions with people who have experience and training in the field in question? You were wrong about this stuff. Get over it already.
Tesseract Posted May 28, 2004 Author Posted May 28, 2004 And this would be your professional opinion' date=' that I should take over all of the textbooks and journal articles I've read, and lectures and discussions with people who have experience and training in the field in question? You were wrong about this stuff. Get over it already.[/quote'] But I dont wanna... I dosnt make sense.
YT2095 Posted May 28, 2004 Posted May 28, 2004 and it never will while you insist upon arguing with proven facts instead of trying to learn and understand something! why don`t you actualy READ the posts and links that have been given to you by extraordinarily patient people, instead of trying to come up with what to say next? THEN you`re in with a chance of learning something
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