4 ms·

Entanglement Makes Quantum Particles Measurably Heavier

17 points by jcr 12y ago

gus_massa 12y ago
> Bruschi’s idea is simple in principle. Physicists have long known that a single quantum particle can exist in two places at the same time. There is a clear quantum correlation called entanglement between these two locations that is well-defined mathematically in quantum mechanics. I don't like this sentence. I've read about entanglement between two particles. I have Math Ph.D. and a 50% Physics major. Can someone with a 100% Physic major explain if this is correct? Is this related to quantum gravity? > Don’t hold your breath, however. Bruschi has carried out some back-of-an—envelope calculations of the size of the effect for a quantum particle with the mass of an electron, of the order of 10^-31 kilograms. He says the change in this particle’s weight when it is entangled in two locations is just one part in 10^[-]37. Inconceivably small. 10^{-37} Kg ~= 56 meV ~=2 mHartrees http://www.wolframalpha.com/input/?i=10%5E%28-37%29kg+*+c%5E2+to+hartree http://www.wolframalpha.com/input/?i=10%5E%28-37%29kg+*+c%5E... In quantum mechanics there are a lot of examples with a lot of correlation (it's similar to like entanglement) and using spectrometry technics I think that it's possible to measure a few mHartrees.
- Retra 12y ago
  What don't you understand? That they are talking about a single particle? A 'single particle in two places' just means the wave-function is distributed into multiple chunks. Entanglement means that two particles' states are not independent. So it seems like that sentence is talking about how two chunks of a particle's wave-function are not independent, which is probably very obvious. The obviousness of that means it's not sexy confusing quantum magic, so you don't hear much about it as much. This guy is suggesting that you might be able measure mass differences dependent on the form of the wave-function, which would be very interesting. That's how I understand it anyway. I could be full of crap.
- ThePhysicist 12y ago
  Yes indeed this sentence seems very wrong to me as well: The author seems to mistake entanglement for superposition. The former describes a quantum state that involves TWO quantum systems whose wave functions are "intertwined" such that you cannot write it as a simple product of the wavefunction of either system (a so-called "product state"), and which thus produces some seemingly paradoxical effects (e.g. the famous Einstein-Podolsky-Rosen paradox). Superposition, on the other hand, means that a SINGLE quantum system can have a wave function in which the system is in more than one possible state at once. Or, in mathematical terms, here's an entangled state |\psi> = 0.5^(1/2)(|0>|1> + |1>|0>) If we would make a measurement of the first quantum state, we would project it to either the |0> or the |1> state. This would result in the state of the other system to be projected into either the |1> or the |0> state, respectively. So there is some strange, "spooky" action between the two seemingly independent states. Here is a superposition state for comparison: |\psi> = 0.5^(1/2)(|0>+|1>) Note that it involves only a single quantum system, which has a 50 % amplitude in either of the states 0 or 1. Wikipedia has some good definitions of entanglement and superposition: https://en.wikipedia.org/wiki/Quantum_entanglement https://en.wikipedia.org/wiki/Quantum_entanglement https://en.wikipedia.org/wiki/Quantum_superposition https://en.wikipedia.org/wiki/Quantum_superposition
- deckar01 12y ago
  The paper is about entanglement, which is not "a single particle that exists in two places at the same time." By definition quantum entanglement "occurs when pairs or groups of particles are generated or interact." [Quantum entanglement](http://en.wikipedia.org/wiki/Quantum_entanglement http://en.wikipedia.org/wiki/Quantum_entanglement) > To summarize, we have shown that entanglement can affect the gravitational field. This suggests that entanglement “has a weight”. The perturbations in the gravitational field depend on the amount of entanglement and vanish for vanishing quantum correlations. The effects studied in this work decay with a time scale proportional to the characteristic “size” of the particle. Furthermore, the contributions to the metric are relevant only if particle positions are not extremely larger than this characteristic size. A prospective theory of quantum gravity must be able to account for this phenomenon and explain its origin. [On the weight of entanglement](http://arxiv.org/pdf/1412.4007v1.pdf http://arxiv.org/pdf/1412.4007v1.pdf)
krick 12y ago
Ugh, I understand that there's limit for how long title could be, but there really is a difference between "Entanglement Makes Quantum Particles Measurably Heavier" and "Entanglement Makes Quantum Particles Measurably Heavier, Says Quantum Theorist". When I saw the title my eyes got wider and I was wondering why it's even on medium, but then I followed the link and saw magic dust fading out. Turns out, nothing really happened. Not yet, anyway.
- cLeEOGPw 12y ago
  I was reading and looking for where the experiments prove the claim in the title, but there is none. Just a theory so far.

17 points by jcr 12y ago

> Bruschi’s idea is simple in principle. Physicists have long known that a single quantum particle can exist in two places at the same time. There is a clear quantum correlation called entanglement between these two locations that is well-defined mathematically in quantum mechanics. I don't like this sentence. I've read about entanglement between two particles. I have Math Ph.D. and a 50% Physics major. Can someone with a 100% Physic major explain if this is correct? Is this related to quantum gravity? > Don’t hold your breath, however. Bruschi has carried out some back-of-an—envelope calculations of the size of the effect for a quantum particle with the mass of an electron, of the order of 10^-31 kilograms. He says the change in this particle’s weight when it is entangled in two locations is just one part in 10^[-]37. Inconceivably small. 10^{-37} Kg ~= 56 meV ~=2 mHartrees http://www.wolframalpha.com/input/?i=10%5E%28-37%29kg+*+c%5E2+to+hartree http://www.wolframalpha.com/input/?i=10%5E%28-37%29kg+*+c%5E... In quantum mechanics there are a lot of examples with a lot of correlation (it's similar to like entanglement) and using spectrometry technics I think that it's possible to measure a few mHartrees.

Retra 12y ago
What don't you understand? That they are talking about a single particle? A 'single particle in two places' just means the wave-function is distributed into multiple chunks. Entanglement means that two particles' states are not independent. So it seems like that sentence is talking about how two chunks of a particle's wave-function are not independent, which is probably very obvious. The obviousness of that means it's not sexy confusing quantum magic, so you don't hear much about it as much. This guy is suggesting that you might be able measure mass differences dependent on the form of the wave-function, which would be very interesting. That's how I understand it anyway. I could be full of crap.
ThePhysicist 12y ago
Yes indeed this sentence seems very wrong to me as well: The author seems to mistake entanglement for superposition. The former describes a quantum state that involves TWO quantum systems whose wave functions are "intertwined" such that you cannot write it as a simple product of the wavefunction of either system (a so-called "product state"), and which thus produces some seemingly paradoxical effects (e.g. the famous Einstein-Podolsky-Rosen paradox). Superposition, on the other hand, means that a SINGLE quantum system can have a wave function in which the system is in more than one possible state at once. Or, in mathematical terms, here's an entangled state |\psi> = 0.5^(1/2)(|0>|1> + |1>|0>) If we would make a measurement of the first quantum state, we would project it to either the |0> or the |1> state. This would result in the state of the other system to be projected into either the |1> or the |0> state, respectively. So there is some strange, "spooky" action between the two seemingly independent states. Here is a superposition state for comparison: |\psi> = 0.5^(1/2)(|0>+|1>) Note that it involves only a single quantum system, which has a 50 % amplitude in either of the states 0 or 1. Wikipedia has some good definitions of entanglement and superposition: https://en.wikipedia.org/wiki/Quantum_entanglement https://en.wikipedia.org/wiki/Quantum_entanglement https://en.wikipedia.org/wiki/Quantum_superposition https://en.wikipedia.org/wiki/Quantum_superposition
deckar01 12y ago
The paper is about entanglement, which is not "a single particle that exists in two places at the same time." By definition quantum entanglement "occurs when pairs or groups of particles are generated or interact." [Quantum entanglement](http://en.wikipedia.org/wiki/Quantum_entanglement http://en.wikipedia.org/wiki/Quantum_entanglement) > To summarize, we have shown that entanglement can affect the gravitational field. This suggests that entanglement “has a weight”. The perturbations in the gravitational field depend on the amount of entanglement and vanish for vanishing quantum correlations. The effects studied in this work decay with a time scale proportional to the characteristic “size” of the particle. Furthermore, the contributions to the metric are relevant only if particle positions are not extremely larger than this characteristic size. A prospective theory of quantum gravity must be able to account for this phenomenon and explain its origin. [On the weight of entanglement](http://arxiv.org/pdf/1412.4007v1.pdf http://arxiv.org/pdf/1412.4007v1.pdf)

krick 12y ago

Ugh, I understand that there's limit for how long title could be, but there really is a difference between "Entanglement Makes Quantum Particles Measurably Heavier" and "Entanglement Makes Quantum Particles Measurably Heavier, Says Quantum Theorist". When I saw the title my eyes got wider and I was wondering why it's even on medium, but then I followed the link and saw magic dust fading out. Turns out, nothing really happened. Not yet, anyway.

cLeEOGPw 12y ago
I was reading and looking for where the experiments prove the claim in the title, but there is none. Just a theory so far.