Paulsrocket Posted January 12 Posted January 12 (edited) You are looking at photons right now in reading this. Now just take it for granted that I entangled one of them. How would you tell it apart from the other trillions of photons, and then to prove entanglement you need to measure it which first means isolating the entangled proton, then measuring it, which would invoke Heisenberg's indeterminacy principle making an accurate measurement if not impossible, at least always suspect. Note, I am not arguing that entanglement happens, just wondering how one would find a proton that is entangled say a million miles away? Edited January 12 by Paulsrocket 2
pzkpfw Posted January 12 Posted January 12 Entanglement experiments start with making two particles be entangled. i.e. you don't entangle one - what's it entangled with? Nor do you need to go looking for the other.
Paulsrocket Posted January 12 Author Posted January 12 5 minutes ago, pzkpfw said: Entanglement experiments start with making two particles be entangled. i.e. you don't entangle one - what's it entangled with? Nor do you need to go looking for the other. You forgot to detail both how the photons are measured to determine spin, nor how the distant photon is found and measured say on a Voyager probe.
J.C.MacSwell Posted January 12 Posted January 12 15 minutes ago, Paulsrocket said: You are looking at photons right now in reading this. Now just take it for granted that I entangled one of them. How would you tell it apart from the other trillions of photons, and then to prove entanglement you need to measure it which first means isolating the entangled proton, then measuring it, which would invoke Heisenberg's indeterminacy principle making an accurate measurement if not impossible, at least always suspect. Note, I am not arguing that entanglement happens, just wondering how one would find a proton that is entangled say a million miles away? First of all good questions for the most part. +1 I'll answer the easy one I bolded. No one would have any practical ideas on how this could be done. The theory is based on much more local experimentation and results. I think there have been experiments done that limit the number of photons, and I think it is somewhat done statistically but others here should give a more accurate answer. `
Bufofrog Posted January 12 Posted January 12 29 minutes ago, Paulsrocket said: How would you tell it apart from the other trillions of photons, and then to prove entanglement you need to measure it which first means isolating the entangled proton, then measuring it I would do it the way the Clauser and Aspect's experiments did it. 33 minutes ago, Paulsrocket said: Heisenberg's indeterminacy principle making an accurate measurement if not impossible, at least always suspect. That is not true. The uncertainty principle say for certain pairs of measurements you cannot give an accurate measurement of BOTH of the attributes at the same time. 35 minutes ago, Paulsrocket said: Note, I am not arguing that entanglement happens, just wondering how one would find a proton that is entangled say a million miles away? You would need some sort of spaceship.
Paulsrocket Posted January 12 Author Posted January 12 5 minutes ago, J.C.MacSwell said: First of all good questions for the most part. +1 I'll answer the easy one I bolded. No one would have any practical ideas on how this could be done. The theory is based on much more local experimentation and results. I think there have been experiments done that limit the number of photons, and I think it is somewhat done statistically but others here should give a more accurate answer. ` I just found this on the net for the longest entanglement yet, but this at least was contained to optical fiber. Physicists from the Austrian Academy of Sciences have succeeded for the first time in entangling photons over 248 kilometers of optical fiber. For quantum communication, this is a new long-distance record and a significant step on the way to the quantum internet. Previously, the maximum distance was 100 kilometers. The last time that I looked over this I predicted that entanglement would be used for communication but all the predictions said that entanglement could not be used for communication for several reasons. So did that change or was I watching all Dis info because this involves military codes and the Chinese appear to have the lead here. I also found another article where China demonstrated entanglement with a satellite at a 1000 kilometer range. 2
J.C.MacSwell Posted January 12 Posted January 12 7 minutes ago, Paulsrocket said: I just found this on the net for the longest entanglement yet, but this at least was contained to optical fiber. Physicists from the Austrian Academy of Sciences have succeeded for the first time in entangling photons over 248 kilometers of optical fiber. For quantum communication, this is a new long-distance record and a significant step on the way to the quantum internet. Previously, the maximum distance was 100 kilometers. The last time that I looked over this I predicted that entanglement would be used for communication but all the predictions said that entanglement could not be used for communication for several reasons. So did that change or was I watching all Dis info because this involves military codes and the Chinese appear to have the lead here. I also found another article where China demonstrated entanglement with a satellite at a 1000 kilometer range. Good find. I wonder what the actual distance was (say maximal distance of any two points of the optical fibre) and how that might affect the results.
StringJunky Posted January 12 Posted January 12 (edited) PaulsRocket. In QComs, entangled elements act as triggers to notify the sender and recipients that the entanglement has been broken, therefore the system has been interfered with. It is purely a cryptographic method and no data has been exchanged. It is sent classically. It's like sticking a piece of hair across a lid and a box to notify if somebody has been in it. Think of it as an alarm. Quote Quantum Communication Quantum mechanics guarantee secure communication Quantum communication is a field of applied quantum physics closely related to quantum information processing and quantum teleportation. Its most interesting application is protecting information channels against eavesdropping by means of quantum cryptography. The most well known and developed application of quantum cryptography is quantum key distribution (QKD). QKD describes the use of quantum mechanical effects to perform cryptographic tasks or to break cryptographic systems. The principle of operation of a QKD system is quite straightforward: two parties (Alice and Bob) use single photons that are randomly polarized to states representing ones and zeroes to transmit a series of random number sequences that are used as keys in cryptographic communications. Both stations are linked together with a quantum channel and a classical channel. Alice generates a random stream of qubits that are sent over the quantum channel. Upon reception of the stream Bob and Alice — using the classical channel — perform classical operations to check if an eavesdroper has tried to extract information on the qubits stream. The presence of an eavesdropper is revealed by the imperfect correlation between the two lists of bits obtained after the transmission of qubits between the emitter and the receiver. One important component of virtually all proper encryption schemes is true randomnessm which can elegantly be generated by means of quantum optics. https://www.picoquant.com/applications/category/quantum-optics/quantum-communication#:~:text=Quantum communication is a field,by means of quantum cryptography. Edited January 12 by StringJunky
joigus Posted January 12 Posted January 12 Strictly speaking, in order to make sure that photons are entangled, you would need: 1) Infinitely many pairs of photons prepared in the same way 2) Perform infinitely many measurements here and in the Voyager or wherever the other place is 3) Talking infinitely many times with the other experimenter and confirming that the correlations are the ones that correspond to such entangled state. The last step is called "sending the classical data" in so-called quantum teleportation experiments. Mind you: Nothing is teleported. It might as well have been called "quantum woodoo" and the phenomenon would be what it is: No woodoo at all, and no teleportation at all. In practice, the "infinitely many" can be substituted by "enough measurements" Measuring just one photon doesn't tell you anything about entanglement. Measuring just once on a pair of photons that are presumably entangled doesn't do anything either.
Markus Hanke Posted January 12 Posted January 12 4 hours ago, Paulsrocket said: You forgot to detail both how the photons are measured to determine spin I’m a bit confused here - over on the other thread on cosmology you seemed to be implying that the theory of relativity is not a good model; yet here you talk about spin, which is a relativistic phenomenon? 5 hours ago, Paulsrocket said: which would invoke Heisenberg's indeterminacy principle In the case of spin, this principle says that you cannot measure more than one component of the spin vector simultaneously with arbitrary precision. You can, however, measure one component plus the overall magnitude of the spin vector simultaneously without problems.
swansont Posted January 12 Posted January 12 12 hours ago, Paulsrocket said: The last time that I looked over this I predicted that entanglement would be used for communication but all the predictions said that entanglement could not be used for communication for several reasons Entanglement can’t be used for faster than light communication, which is the usual proposal
Paulsrocket Posted January 12 Author Posted January 12 12 hours ago, Markus Hanke said: I’m a bit confused here - over on the other thread on cosmology you seemed to be implying that the theory of relativity is not a good model; yet here you talk about spin, which is a relativistic phenomenon? In the case of spin, this principle says that you cannot measure more than one component of the spin vector simultaneously with arbitrary precision. You can, however, measure one component plus the overall magnitude of the spin vector simultaneously without problems. Nima Arkani-Hamed at the Max Planck institute for physics in Munich THE END OF SPACETIME. Be sure to let him know what you disagree with https://www.youtube.com/watch?v=GL77oOnrPzY&t=1802s -1
Bufofrog Posted January 12 Posted January 12 41 minutes ago, Paulsrocket said: Nima Arkani-Hamed at the Max Planck institute for physics in Munich THE END OF SPACETIME. I don't want to watch a Youtube. Since this is a discussion forum perhaps you could let us know what in the video you find interesting. 1
swansont Posted January 12 Posted January 12 8 hours ago, Paulsrocket said: Nima Arkani-Hamed at the Max Planck institute for physics in Munich THE END OF SPACETIME. Be sure to let him know what you disagree with https://www.youtube.com/watch?v=GL77oOnrPzY&t=1802s It’s unreasonable for you to expect anyone to watch a 50 min video and sort through the arguments, which is why we have a rule against it On 1/11/2024 at 9:33 PM, joigus said: Measuring just one photon doesn't tell you anything about entanglement. to add to this: measuring one photon doesn’t even tell you it’s entangled On 1/11/2024 at 9:33 PM, joigus said: Measuring just once on a pair of photons that are presumably entangled doesn't do anything either. It could possibly rule out entanglement, since the correlation could come out wrong. But that’s it
Ghideon Posted January 12 Posted January 12 2 hours ago, Paulsrocket said: Nima Arkani-Hamed at the Max Planck institute for physics in Munich THE END OF SPACETIME. Be sure to let him know what you disagree with https://www.youtube.com/watch?v=GL77oOnrPzY&t=1802s The video, which delves into quantum mechanics and theoretical physics, does not mention 'photons' at all in the transcript. Can you explain how the video is relevant? (Note: thanks to machine learning and NLP I did not watch the video)
Paulsrocket Posted January 13 Author Posted January 13 (edited) 5 hours ago, Bufofrog said: I don't want to watch a Youtube. Since this is a discussion forum perhaps you could let us know what in the video you find interesting. I find every lecture at or from the Max Plank Institute fascinating and everything in the 50-minute lecture equally fascinating. So, if a Max Planck quantum physicist does not interest you, neither would I repeating the same stuff. 3 hours ago, Ghideon said: The video, which delves into quantum mechanics and theoretical physics, does not mention 'photons' at all in the transcript. Can you explain how the video is relevant? (Note: thanks to machine learning and NLP I did not watch the video) I came across the lecture while searching several ideas at once, I merely found the topic fascinating and thought that others might share my yearning for knowledge. I have found the lack of a quantum theory of gravity to be a gaping hole and as to whether it is related to entanglement, I can't be sure, just as I am still not sure how to measure the spin of a photon that is always moving at c. So how does anyone measure the spin of something moving at c or light speed? Do you know, because I do not Edited January 13 by Paulsrocket
Bufofrog Posted January 13 Posted January 13 1 hour ago, Paulsrocket said: So how does anyone measure the spin of something moving at c or light speed? Do you know, because I do not Using a polarizer. You can easily look it up, just google, "how to measure the spin of a photon". You seem to have this attitude that if you don't know something or if it doesn't make sense to you then it must be wrong. 1
Paulsrocket Posted January 13 Author Posted January 13 (edited) 26 minutes ago, Bufofrog said: Using a polarizer. You can easily look it up, just google, "how to measure the spin of a photon". You seem to have this attitude that if you don't know something or if it doesn't make sense to you then it must be wrong. Do you have a research paper and link to that? I actually have several polarizing lenses for my Nikon. Polarizing filters have the property of transmitting light that vibrates in one direction while absorbing light that vibrates in a perpendicular direction. These filters are used extensively in scientific instruments. In sunglasses and when placed over a camera lens, polarizing filters reduce unwanted reflections Doesn't say anything about measuring the spin of one individual entangled photon moving 186,000 miles per second. Edited January 13 by Paulsrocket
Bufofrog Posted January 13 Posted January 13 (edited) 6 minutes ago, Paulsrocket said: Doesn't say anything about measuring the spin of one individual entangled photon. Ha ha, it sure doesn't. Do you know what a bad faith argument is? Edited January 13 by Bufofrog
Paulsrocket Posted January 13 Author Posted January 13 (edited) 35 minutes ago, Bufofrog said: Ha ha, it sure doesn't. Do you know what a bad faith argument is? The spin of a photon is measured by making polarization measurement. If we measure the linear polarization of a single photon along any axis, we can only find it aligned with the axis or perpendicular to this axis. If we measure the linear polarization of photons along any axis, there are only two possible results. It says if we measure the spin of a photon. NOT THAT ANYONE EVER ACTUALLY HAS It does not say how this is accomplished and it does say that one photons spin can be measured. So do you know, besides if the measurement takes 1 full second to complete the photon is 186,000 miles away at the end of the second, which raises another question as to how long does it actually take to measure a photon, and how long is the measuring device, which would yield the time that it is actually there. Do you know? Edit, a polarizer is approximately 3mm wide, so 3mm=3.171e-19 light years. Edited January 13 by Paulsrocket
swansont Posted January 13 Posted January 13 2 hours ago, Paulsrocket said: I find every lecture at or from the Max Plank Institute fascinating and everything in the 50-minute lecture equally fascinating. So, if a Max Planck quantum physicist does not interest you, neither would I repeating the same stuff. The issue that’s all to common is that interested amateurs watch a video but it’s not saying what they think it’s saying. Saying that the whole lecture is fascination isn’t the issue here - what is in the video that pertains to this particular discussion. It’s unlikely that all 50 minutes are.
Paulsrocket Posted January 13 Author Posted January 13 2 minutes ago, swansont said: The issue that’s all to common is that interested amateurs watch a video but it’s not saying what they think it’s saying. Saying that the whole lecture is fascination isn’t the issue here - what is in the video that pertains to this particular discussion. It’s unlikely that all 50 minutes are. What exactly is space time not connected too?
swansont Posted January 13 Posted January 13 1 hour ago, Paulsrocket said: It says if we measure the spin of a photon. NOT THAT ANYONE EVER ACTUALLY HAS Because that’s trivially known, if you’re familiar with atomic physics. Your tone suggests that you think it hasn’t been done. I’ve done it. One way is to send it through a polarizing beam-splitter cube. If the polarization is in one direction it goes straight through. If it’s orthogonal it gets reflected. Knowing which way it goes tells you the polarization 2 minutes ago, Paulsrocket said: What exactly is space time not connected too? I have no idea of the context of this question, but spacetime means you’re talking about relativity, and entanglement is a quantum effect. So you need to explain the connection. 2
Paulsrocket Posted January 13 Author Posted January 13 2 minutes ago, swansont said: Because that’s trivially known, if you’re familiar with atomic physics. Your tone suggests that you think it hasn’t been done. I’ve done it. One way is to send it through a polarizing beam-splitter cube. If the polarization is in one direction it goes straight through. If it’s orthogonal it gets reflected. Knowing which way it goes tells you the polarization How do you know that the photon that you measured is the entangled one, or do you send one photon, and if you do that how do you isolate one photon? 1
swansont Posted January 13 Posted January 13 1 hour ago, Paulsrocket said: It does not say how this is accomplished and it does say that one photons spin can be measured. So do you know, besides if the measurement takes 1 full second to complete the photon is 186,000 miles away at the end of the second You’d probably send the light through an optical fiber, which can be coiled up, and the measurement takes much less than a second. Just now, Paulsrocket said: How do you know that the photon that you measured is the entangled one, Because you entangled the photons. As you’ve been told, if it’s just a random photon there’s no way to tell if it’s entangled Just now, Paulsrocket said: or do you send one photon, and if you do that how do you isolate one photon? Again, as you’ve been told, you need multiple photons to do this. You really need to read the replies in the thread.
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