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Chinese Researchers Achieve Quantum Entanglement Record

scientificamerican.com

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Re: Chinese Researchers Achieve Quantum Entanglement Record

#31
post #25
post #24

Earlier quoted context omitted.

The part I don't understand is the "spooky action at a distance." Isn't this just the same as if the qbits were already in whatever their final state was as soon as they were entangled? Or in other words, is there any experimental basis for determining that the "cat" stayed alive at all? It seems a lot less magical when we just determine that in fact the value is the same no matter when or where you measure it, altho…

The idea that the qbits choose which value they'll collapse to at time of entanglement is called local hidden variable theory, which John Bell disproved in 1964: https://en.wikipedia.org/wiki/Local_hidden_variable_theory In more practical terms, the theory also falls apart when you start doing more complicated things with entangled qbits than just measuring them, like quantum teleportation or error correction.

So, it's kind of like closures in JavaScript?

"A Bell test experiment or Bell's inequality experiment, also simply a Bell test, is a real-world physics experiment designed to test the theory of quantum mechanics in relation to two other concepts: the principle of locality and Einstein's concept of "local realism". The experiments test whether or not the real world satisfies local realism, which requires the presence of some additional local variables (called "hidden" because they are not a feature of quantum theory) to explain the behavior of particles like photons and electrons. According to Bell's theorem, if nature actually operates in accord with any theory of local hidden variables, then the results of a Bell test will be constrained in a particular, quantifiable way. If a Bell test is performed in a laboratory and the results are not thus constrained, then they are inconsistent with the hypothesis that local hidden variables exist."

Spooky private method scope is spooky.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#32
post #13

Crash course in entanglement: The state of each qbit is represented by a state vector of two complex numbers [a, b] where |a|^2 + |b|^2 = 1. There are two special qbit values called the classical basis : [1, 0] which is the classical bit 0, and [0, 1] which is the classical bit 1. If a qbit is not in one of the two classical states, we say it is in superposition . When a qbit is in superposition, we can measure it[0]…

I think this video deserves much more attention by HN readers, it's truly great introduction into quantum computing.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#33

Even neater is that they are using quantum entanglement in radar to detect stealth planes: https://www.popsci.com/china-quantum-radar-detects-stealth-p...

Yea, you have to explain this. It made no sense when I first read it, and it still makes no sense.

Here is how radar works: You shine a flashlight somewhere. If there is an object within range, some of the light is reflected back at you and you know there is an object. This is literally what radar does.

So, what part of this, and how, does this "quantum" magic affect?

Re: Chinese Researchers Achieve Quantum Entanglement Record

#34
post #25
post #24

Earlier quoted context omitted.

The part I don't understand is the "spooky action at a distance." Isn't this just the same as if the qbits were already in whatever their final state was as soon as they were entangled? Or in other words, is there any experimental basis for determining that the "cat" stayed alive at all? It seems a lot less magical when we just determine that in fact the value is the same no matter when or where you measure it, altho…

The idea that the qbits choose which value they'll collapse to at time of entanglement is called local hidden variable theory, which John Bell disproved in 1964: https://en.wikipedia.org/wiki/Local_hidden_variable_theory In more practical terms, the theory also falls apart when you start doing more complicated things with entangled qbits than just measuring them, like quantum teleportation or error correction.

It’s also worth noting that as of 2015[0], this has been experimentally verified.

We’ve made real-world measurements here that correlate with measurements made at the exact same time over there in a way that mathematically cannot be accounted for without some species of intuition-violating spookiness. It’s all very real.

0: https://en.wikipedia.org/wiki/Bell_test_experiments#Hensen_e...

Re: Chinese Researchers Achieve Quantum Entanglement Record

#35
post #30

Earlier quoted context omitted.

Also, if they got it to work they would surely keep it secret.

Also, if they didn't get it to work they would surely keep it secret.

Yes, and if the military was involved at all, they wouldn’t even talk about the possibility.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#36
post #18

Earlier quoted context omitted.

Problems that are waiting to be solved by it are very large and of huge impact I know virtually nothing about quantum computing, so can you give some examples? Whenever I've asked anyone who seemed to know anything about the field, all they can come up with is weather forecasting and simulating nuclear explosions. Not exactly "general use," as you put it. In the back of my mind, I know that quantum computing is a big…

There are already lots of 'practical' applications in the literature. A famous one is Shor's factorisation algorithm. But there are others - everything from doing pagerank to simulating other quantum systems. Many classical algorithms, which run in ~O(poly(n)) can have an 'equivalent' quantum algorithm in ~O(log(n)) - an exponential speedup. There is still debate as to how the complexity class of problems which are e…

I'd also add that the need for localized personal computing services goes down as network bandwidth increases, if there's anything that people really need quantum computers for, it's not unreasonable to suggest that they will be handled on the backend with aggregated results sent to clients as is the case for most computation today.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#37
post #22
post #18

Earlier quoted context omitted.

There are already lots of 'practical' applications in the literature. A famous one is Shor's factorisation algorithm. But there are others - everything from doing pagerank to simulating other quantum systems. Many classical algorithms, which run in ~O(poly(n)) can have an 'equivalent' quantum algorithm in ~O(log(n)) - an exponential speedup. There is still debate as to how the complexity class of problems which are e…

Is Shor's an application of entanglement though?

Yes, all non-trivial quantum computing is based on entanglement.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#38
> “It’s as though you took six bits in your computer, but each bit tripled in how much information it could hold,” Schreppler said

"Each bit is tripled in how much information it could hold"? Normally bits have two states, but Shreppler is claiming these qubits can have six states? What am I missing?

Re: Chinese Researchers Achieve Quantum Entanglement Record

#39
post #28

Question: Why superfluid 4He is not quantum-entangled? What differentiates macroscopic many-body quantum states from many-body quantum entanglement?

Superfluid 4He is quantum-entangled and non-local effects are observable. https://www.sciencedaily.com/releases/2017/03/170321110344.h...

Re: Chinese Researchers Achieve Quantum Entanglement Record

#40
post #15

Earlier quoted context omitted.

We all have these things in our pockets that are massive supercomputers by the standards of my college days. And we all use them just to rant at each other about political things that we in reality are totally misinformed about ... and otherwise just waste our lives. I am not sure why quantum computing is supposed to change this. Even software that is supposed to be useful is so terribly slow. Computers are between 2…

> And we all use them just to rant at each other about political things that we in reality are totally misinformed about ... and otherwise just waste our lives. So if I decide to use the device that I have bought and invested in, to "rant" about something (to connect to other people through it, essentially), or even just connect to my loved ones sending "meaningless" information (as many I'm sure would call it), or i…

JIN YAAAAAAAANG!!!!
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