Chinese Researchers Achieve Quantum Entanglement Record • Hacker News Board

Re: Chinese Researchers Achieve Quantum Entanglement Record

#51

Post by whatshisface » Tue, Jul 17, 2018, 6:47 PM UTC

tzakrajs wrote: post #43

albertgoeswoof wrote: post #41

Earlier quoted context omitted.

I thought qubits had an infinite range of states?

Oh yeah, thats right.. Isn't it based on orientation in a spherical sense? I guess you could have an infinite number of those orientations.

A pure quantum state is a basis vector, written like |n>. It's called a basis vector because it shares a list of mathematical properties with the x̂,ŷ,ẑ coordinate basis vectors you might be familiar with.

They can be combined, (like coordinate vectors) by writing coefficients before them. For example, 1/√2 |a> + 1/√2 |b> would be a combination of state a and state b. Combinations of states obey the condition that the sum of the squares of each coefficient equals one. This is the unitary constraint, and above you can see that 1/√2^2 + 1/√2^2 = 1/2 + 1/2 = 1.

Coefficients can be complex numbers, which consist of a real part and an imaginary part.

So, putting all of this together, a qbit that may be in the state |1> or the state |0> may also be in the state (a+bi)|1> + (c+di)|0>. With the unitary constraint, we can cut out a degree of freedom by introducing the equation |a+bi|^2 + |c+di|^2 = 1. This leaves three degrees of freedom, which can be mapped in to a sphere by a change of coordinates. Three spherical coordinates plus the unitary constraint specifies the four-number state combination.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#52

Post by crumpington » Tue, Jul 17, 2018, 6:48 PM UTC

ahelwer wrote: post #25

bdamm wrote: 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.

Big deal. There's nothing shocking or spooky about two billiard balls being made to spin in arbitrarily opposing directions, selecting only one (omg! without discovering which way it spins, you guys), then separating them, and then noticing the spin of one, in order to reliably grasp that the other is the reversal.

I have two guitars. I place the guitars facing one another, such that plucking the HIGH E string on one, also plucks the LOW E string on the other. We put ear plugs in our ears, such that I can separate the two guitars, without us ever hearing them. I pluck the guitars, give you one, and take the other one and travel far away. I then listen to my guitar. It is the HIGH E guitar. Now I know you have the LOW E guitar. Wow. Incredibly unspooky. Not teleportration.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#53

Post by lisper » Tue, Jul 17, 2018, 6:49 PM UTC

ahelwer wrote: post #25

bdamm wrote: 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.

Something else worth noting: an entangled state is itself a superposition of two non-entangled states. This is obvious when you look at the math: the entangled state |10> + |01> is the superposition of the factorizable (non-entangled) states |10> and |01>. But physically what this means is that entanglement is intimately related to interference. Interference happens when a photon "goes both ways". Entanglement happens when a pair of photons go in such a way that you can't tell which photon went which way. (There's more to it than that, but the point is that entanglement and interference are closely related phenomena. This fact is often overlooked, particularly when it comes to explanations of entanglement directed at lay audiences.)

Also, the idea that collapse is a physical phenomenon that propagates faster than light is not universally accepted. There are other ways to interpret these results. None of them take a toll on your intuition, but personally I like this one:

http://www.flownet.com/ron/QM.pdf

(There's a video too: https://www.youtube.com/watch?v=dEaecUuEqfc)

Re: Chinese Researchers Achieve Quantum Entanglement Record

#54

Post by nabla9 » Tue, Jul 17, 2018, 6:52 PM UTC

barbegal wrote: post #50

nabla9 wrote: post #44

Earlier quoted context omitted.

So why it's not taken into account when quantum-entanglement records are broken? You can have flasks of superfluid 4He with thousands of moles of entangled atoms clearly visible.

Quite correct but usually quantum-entanglement records are for qubits rather than generic atoms. And qubits must be able to be measured in isolation e.g. the polarisation of a single photon can be measured. With superfluid 4He you can't isolate the qubits.

Ah, that makes sense. Thank you.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#55

Post by _match » Tue, Jul 17, 2018, 6:54 PM UTC

jblow wrote: post #15

ssdd wrote: post #6

Earlier quoted context omitted.

That's great. Now next thing that needs to be solved is to make this tech available for general public use just like computers are these days. Problems that are waiting to be solved by it are very large and of huge impact.

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…

Honestly, I'd love to see examples of rotted code that could be made exponentially faster. I'm likely guilty of this.

And I agree that it's disheartening to watch how horribly we use these incredible tools. But thankfully as programmers we're in a position to design these tools to offset the worst parts of humanity.

And one field in which more powerful computers will be needed soon is deep learning. It appears that progress is beginning to stall, as larger networks are necessary. Better tools for distributed computing will make up the difference in the short term, but the current infrastructure appears to be insufficient for general intelligence.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#56

Post by aaavl2821 » Tue, Jul 17, 2018, 6:56 PM UTC

dzhiurgis wrote: post #49

bscphil wrote: post #19

Earlier quoted context omitted.

What's the size needed for cracking large-primes based encryption? If not at 100 qubits, what are some useful calculations that we can do at that size?

A lot of things regarding chemistry and biology - finding catalysts for nitrate fertiliser production (uses 5% of worlds power), perhaps some catalysts in cement production (my idea), invention of new medicines, either due to better cell simulations or (my idea) faster protein folding.

Is the bottleneck preventing better cell simulations computational or lack of data / insufficient understanding of biology to inform a predictive model?

Re: Chinese Researchers Achieve Quantum Entanglement Record

#57

Post by ams6110 » Tue, Jul 17, 2018, 7:04 PM UTC

jblow wrote: post #15

ssdd wrote: post #6

Earlier quoted context omitted.

That's great. Now next thing that needs to be solved is to make this tech available for general public use just like computers are these days. Problems that are waiting to be solved by it are very large and of huge impact.

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…

We would not have Amazon, Netflix, Youtube, Facebook, Google Docs, Deep Learning, name any other modern software technology or product, if we were still writing and optimizing everything by hand in assembly or C. Those "2 to 4 orders of magnitude" that are "sitting on the table" are actually being used to make it possible for developers to work at a much higher level and be much more productive.

I totally agree with your first paragraph, though.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#58

Post by ChrisClark » Tue, Jul 17, 2018, 7:05 PM UTC

crumpington wrote: post #52

ahelwer wrote: post #25

Earlier quoted context omitted.

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.

Big deal. There's nothing shocking or spooky about two billiard balls being made to spin in arbitrarily opposing directions, selecting only one ( omg! without discovering which way it spins, you guys ), then separating them, and then noticing the spin of one, in order to reliably grasp that the other is the reversal. I have two guitars. I place the guitars facing one another, such that plucking the HIGH E string on o…

https://en.wikipedia.org/wiki/Local_hidden_variable_theory

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

Re: Chinese Researchers Achieve Quantum Entanglement Record

#59

Post by sgc » Tue, Jul 17, 2018, 7:05 PM UTC

Erlich_Bachman wrote: post #27

jblow wrote: 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…

I think many people would find intellectually boring your position of absolute personal freedom with no objective measure of excellence, along with your aggressive defense of such. But there is also objective information which would support OP's position for someone who considers objectivity in the personal sphere of little value: heavy computer and mobile use has been linked many times with psychological difficulties, including anxiety, depression, stress, etc. Please don't pontificate on other's allusion to human well being by presenting your own moral code to be imposed.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#60

Post by otakucode » Tue, Jul 17, 2018, 7:12 PM UTC

jblow wrote: post #15

ssdd wrote: post #6

Earlier quoted context omitted.

That's great. Now next thing that needs to be solved is to make this tech available for general public use just like computers are these days. Problems that are waiting to be solved by it are very large and of huge impact.

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…

The introduction of automobiles permitted the development of F1 racecar drivers, but just ended up with most people dragging themselves around to get food and money. The introduction of the printing press permitted the publication of pamphlets and books that overturned world governments and dethroned kings... but most people used it to trade porn and recipe books.

Technology doesn't make people better. It lets people do better things if they have the desire to do so. It also must enable them to do worse things if they have the desire to do so. You can not have one without the other. And on the balance things have historically gotten better so there's not too much reason to be worried about the fact most people just use global communication to bicker. They won't be remembered. Those who are, however, wouldn't have been possible otherwise.

As for where quantum computing factors into this, I don't have the slightest clue.