One Photon In, TWO Photons Out
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- Опубліковано 6 чер 2024
- A fascinating phenomenon with a forbidding name (parametric down conversion) occurs in certain crystals. A single photon enters, but two emerge. There are myriad pair combinations; but in each case, the sum of the total energy and momentum of the two output photons exactly equals those of the single input photon.
Parametric down conversion is finding a host of uses in physics, from testing the efficiency of high-tech single-photon detectors to cutting-edge experiments in quantum mechanics.
Alan Migdall of the National Institute of Standards and Technology explains and demonstrates how it's done. - Наука та технологія
You know this is a real research lab when you incorporate rubber bands or tape into your optical systems. I'm starting to miss living in the lab.
Bravo, Ryan! How are you doing lately?
Best explanation I've ever seen of exactly how we are about to produce and detect/use a single photon at a time. Spontaneous parametric down conversion makes so much more sense now!
Im confused... Everyone is complimenting how well explained this is, but when is it explained HOW one photons split in to two?
It isn't and technically the process is not even possible because of angular momentum conservation. It's one photon in, something happening to the bulk of the conversion crystal and then two photons out. That "something" is the hard part.
Isn’t it essentially similar to crystalline structures and it’s similar to complex mirrors reflecting light?
photon hits the atoms of the material and is absorbed, the material then reacts to that by emitting two lower energy photons.
Have you got a video on double slit experiment that explains exactly how the detectors work more in depth most videos don’t go into enough details but yours seem fabulous
This is the best explanation I've seen on this. I've seen heaps of animations and written explanations, but seeing the apparatus in action really puts it into perspective.
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I don't know why UA-cam wanted me to watch these videos but I just bought two books from photonics media. This comment is for the people 10000 years in the future to find.
Wow finally explanation given on UA-cam at a level that is useful
Rubber bands on photonics parts on a rusty optics table - at NIST...I no longer feel bad about my lab ; )
Nice work guys, just having fun, learned a lot here, as others have said by seeing the actual setup.
The jazz at the end was the icing on the cake, marvellously made vid, more more pls
My mind wandered to entanglement possible application ?
Great to see how entangled photons get created, with all the nitty gritty details.
Just wondering, does the down conversion of say a blue laser only produce Light with color lower than itself, and/or does it emit other waves non-visible on the spectrum like infrared?
If so how far would it move into the infrared section of the spectrum, would it produce microwaves sometimes?
I've read about experiments on quantum entanglement where they start with a photon, pass it through a crystal, and two entangled photons emerge. Is the parametric down conversion the same phenomenon? I hope so, or else I'm back to wondering exactly how the experimenters get entangled photons.
You've got it right. There are some additional tricks to get specific types of entanglement, but 1 photon to 2 within the crystal is the basis of many entanglement setups.
Great to see these explanations. The science literature can be so obtuse, and without this kinds of common sense hands on, people give up on it before they have a chance to learn what its all about.
michrowave the proton the blue one
It's purposefully obtuse. Keeps people in a job if it's made excessively complex.
finally a video which explains parametric downconversion
.
If we turn down the intensity of the input beam does the fraction, one in a million or one in a billion still hold? Is the down converted beam power proportional to the input beam power or is the output beam power a non-linear function of the input beam power?
Thank you.
Great question, I'd love to hear the answer to this.
Very informative. Thanks.
Is there a relatively cheap or common substance that can produce parametric down conversion? I've heard of beta barium borate, but it's a bit expensive. I'm looking for something that can demonstrate the principle, it doesn't have to be very high quality. Thanks.
I worked on down conversion in lab as an undergrad for 2 1/2. We used it to recreate Grangers proof of the photon
1:55 why does the graphic scale illustrate wl as a negative exponent?
Can you put entangled photons through a fiber optic cable?
Is one a split in color band vs brightness degradation
When you compare the real lab Mach Zehnder Interferometer with its counterpart the computer simulator would you say that it is possible to do experiments with the latter that would be scientifically reliable or viable as if you did the very same experiment in a real lab with a real MZI?
Yes!
What happens if you were to. put. 2 Crystal's where the photons split. Could you split the two photons that were previously split into 3 or 6.
To Alan Migdall: Excellent reality experiment with physically logical explanations. Thank you. Please make more videos if you have more things to explain. Most other fundamental physics explanations are loaded with physically illogical quantum mechanics and relativity theory assumptions which never logically explain anything. A question I hope you might be able to answer is, if a single photon impinges on a surface of a refractive medium, does it partly refract and partly reflect, or does it either only completely refract or only completely reflect?
Good question.
If you put one photon-counting detector in the transmitted path and another detector in the reflected path, you will have your answer. A single photon can only be detected in one of the two detectors. That is, it can only completely reflect or be completely transmitted. That is what it means for the photon to be a single particle.
If the reflectance of the surface is, say 4 % (that is something you can measure classically), then 4 % of the time the detector in the reflected path will click and 96 % of the time the transmitted path detector will click. Each time you do the experiment with a single photon input there is no way of knowing which outcome will happen. You only know the probabilities.
@@alanmigdall8697 Thank you very much. That was my best educated guess, but it was only a guess. You've now revealed a 2nd excellent reality experiment with physically logical explanations. Many other people like myself have been searching the internet unsuccessfully for the important results of that reality experiment. You might consider demonstrating and explaining that experiment yourself on UA-cam. Many people could benefit from it, especially if your title and keywords make it easy for people to find the video. I might suggest a title and/or keywords including "single photon refraction reflection". If you are not interested in making such a video, perhaps you know a colleague who might be?
I notice a comment here by natalie1111111able Potter, who enquires if you have a video detailing how the detectors in double slit experiments work. I am also very curious about this. If such a video has not already been made, I personally would prefer you to be the 1 to make it, as I very much appreciate your physically logical explanations.
Regarding your own experiment you've demonstrated and explained here, it's helpful to me to learn how energy and momentum are conserved in photon-photon interactions. I've invented a unifying physics theory, matter theory. I have 8 videos on UA-cam promoting it for funding. If I can possibly help you, please contact me.
To Alan Migdall: I am curious again about your own reality experiment. In parametric down conversion, what exactly causes 1 photon to split into 2 photons conserving momentum and energy? And, can your experiment be done in reverse, parametrically up converting 2 photons into 1 photon?
@@joshuahong4921 I don't know what it might be called.
@nickharvey7
You can only collapse the wave form once and "produce" one particle. If you set up many detectors only one of them will detect the particle.
What’s observed when Twin Protons are put through the Double Slit experiment.
Is it possible generate a chain reaction with the cristal in a ressonant chamber?
No. The efficiency of the conversion process is on the order of parts in a million and the energy of the output photons is wrong and can't lead to a second split in the same crystal.
@@schmetterling4477 Thank you.
Interesting video! Is the photon a wave until it comes in contact with a detector? I was thinking that the more detectors you set up the more places you will collapse the wave function. Therefore the more photons you will create or form.
Any discrete measurement of a wave can look like a particle, or a quantized unit. This does not mean the photon changes. It was and always is a packet of electromagnetic energy.
Thank you!
I just want to know are they quantumly entangled?
02:50 Assumes the efficiency of the lower detector is 100%. If the efficiency of the lower detector is less than 100%, then the upper detector can click when the lower one doesn't.
Now *this* is a science video, to hell with thenewscientist and their gadgets.
Thanks for the upload, this is quality.
Are you still doing Experiments? I'd like to chat!
I have answers now.
I have more questions now.
This is good.
>>--------------------> I wonder what fantastic future studies and/or applications will be obtained by "holding" a photon and its quantum twin in a solid state? Sounds incredible.
You are looking at a stream of photons, not a single photon. How many photons enter the crystal each second? trillions and trillions. How many come out each second?
That's just an efficiency question. One can probably make much more efficient converters and eventually somebody will.
If photons are fundamental particles, how can you split them in two? Wouldnt that contradict the definition of 'photon'?
There are no particles. Photons are field energy.
@@lepidoptera9337 Even if I accept that, how can they then be quantified?
@@numbynumb Energy is actually not quantized (it is observer dependent, just like in classical physics. hence we get doppler shift for photons just as well as for classical waves). Angular momentum and spin are quantized. It just happens that energy, momentum and angular momentum/spin are joint at the hip by special relativity, so whenever systems change their angular momentum by a discrete step, they also have to change their energy by a step.
@@lepidoptera9337I think some energy like photons can be quanitzed. Otherwise he would only be assuming that the output are two equal halves of the energy instead of an unknown output from the material lattice
@@patrickday4206 Quantization means that a physical property can only come in the exact same amounts (or multiples thereof), like in case of angular momentum or charge (all spins and all electrical charges are exactly the same for all we know). Energy can come in any amount. It's not quantized. A photon is a discrete amount of energy, but its energy is not what is quantized. Only its angular momentum is.
In theoretical physics, what if photon is actually two photons sharing the same room.
Then you get a point deduction in your test for not understanding angular momentum conservation.
Some people have suggested that light may travel in a helix two entangled could collapse into one partical correct?
I don't get the mystery then.
Let's you randomly break up a meter stick into two non-equal pieces.
The sum of both will equal the input
So... if I measure one broken stick at .3 meters.....
NO MATTER HOW FAR AWAY THAT OTHER STICK GOES..... it will always be .7 meters.
So.... why is it a mystery thet entangled photons have opposite spins if they're meant to add up to the whole?!!!
It's not a mystery. The only mystery is why people don't want to understand that photons are changes in energy and not objects. :-)
One cannot subdivide a photon
Guy is making wrong statement by saying one photon in and 2 out
That is correct. Conservation laws require that something else is happening. That's what we need the conversion crystal for... to account for the momentum and angular momentum balance.
no impossible. a photon can no be detected without energy added to the detector. input can not equal output in this case. if you get two photons out it will have twice the energy of the input due to the extra energy of the detector. the equation is not experimentally provable. you can not detect the energy of a photon only its presence and location. you can only detect the energy released by a electrons in a photon exchange.
We are teaching in high school that "the photon" is the amount of energy detected by the detector. A photon is not some "thing" that has energy. It IS the energy that gets irreversibly absorbed from the electromagnetic field by the matter of the detector. I still can't get my head around how hard it must be for people to differentia the meaning between "something being" and "something having" in the English language. ;-)
NICE THAT HE SHOWED THE APPARATUS. BUT WHY DIDN'T HE SHOW WHAT HE WANTS US TO BELIEVE? THIS IS PHYSICS, RIGHT?
I worked on down conversion in lab as an undergrad for 2 1/2. We used it to recreate Grangers proof of the photon
I don't know how that experiment is supposed to "prove" photons... since the non-linear optical crystal can certainly "split" a photon in two. Not to mention that photon number is not conserved under any circumstance, neither in low energy (emission, absorption, thermal radiation) or high energy physics. That the photon number is (almost) constant on a beam splitter is a special property of the beam splitter. It proves nothing particular about the electromagnetic field. :-)
@@schmetterling4477 The proof wasn't on properties of the photon, it just set up an experiment where the only possible scientific explanation for the outcome is the photon. As far as I am aware other experiments that between Einstein's 1905 proposal of the photon and Grangier's 1985 experiment could only tangentially prove the photon. Our experiment was recreating the 1985 experiment consistently with comparatively inexpensive equipment (>15,000$). The book we used for reference was "Quantum Mechanics: Theory and Experiment" by Mark Beck. We used different equipment, we added an experiment to test the sensitivity of our equipment and did experiments 1&2 as well as parts of 3&4.
@@loganreidy7055 That "other experiments don't prove field quantization" is absolute nonsense. The best proof we have for field quantization is the stability of matter. Classical theories can not account for that.