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Chinese Researchers Achieve Quantum Entanglement Record

scientificamerican.com

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Re: Chinese Researchers Achieve Quantum Entanglement Record

#21

Post by ahelwer »

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…

Quantum computers won't change anything about people posting misinformed political opinions.

Three orders of magnitude speedup is a constant factor. Quantum computers provide between sqrt(n) and log(n) speedup depending on the problem - for example, biochemistry simulation for improved drug designs and such. That seems worthwhile.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#22

Post by bdamm »

foxes wrote: post #18
reaperducer wrote: post #8

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…

Is Shor's an application of entanglement though?

Re: Chinese Researchers Achieve Quantum Entanglement Record

#23

Post by deepGem »

bscphil wrote: post #19
foxes wrote: post #4

I visited USTC several years ago, (2014) and in this time they have basically doubled the number of qubits they can entangle, so this is a great step forward. At around ~100 qubits quantum computing becomes very useful, so maybe we won't have to wait too long.

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?

So the number of raw qubits are in the order of a million for large prime factorization or to make Shor's algorithm a reality. This is because the physical qubits are highly unstable and prone to errors. The error correction methodologies will result in a fault-tolerant logical qubit. Depending on the error correction algorithm, the ratio of logical: data/physical qubit is 1:1000 at the minimum. You need 4000 logical qubits at least for large prime factorization give or take 4 million raw qubits.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#24

Post by bdamm »

ahelwer wrote: 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]…

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, although it may not be predictable. And since the "entangled" qbit always had the same value, no matter when you measured it, then there is no "spooky action at a distance". The action occurred when d=0, and what you actually have is two copies of the same ROM.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#25

Post by ahelwer »

bdamm wrote: post #24
ahelwer wrote: 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]…

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.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#26

Post by Cobord »

ssdd wrote: post #6
foxes wrote: post #4

I visited USTC several years ago, (2014) and in this time they have basically doubled the number of qubits they can entangle, so this is a great step forward. At around ~100 qubits quantum computing becomes very useful, so maybe we won't have to wait too long.

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.

Because of the expense it will have to start off as QCaaS. You send the really hard part of your problem to whichever person actually has the hardware and they'll return the answer. If you are concerned with them not knowing your data, there are workarounds to that as well. So available to general public in a weaker sense.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#27

Post by Erlich_Bachman »

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…

> 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 if I choose to use it for anything else, who is to say that it's "wasting my life"? You? Why do you decide what is wasteful and what is not? Maybe all those people want to do those things?

You can't say that this technology is wasted or is not used properly without also implicitly assuming moral and philosophical authority about what people should choose and not to choose with their time and other resources, including the money used to buy such devices and resources spend on developing them. Why do you assume that you can be such an authority?

Of course, looking at this in another way, you definitely have the ultimate authority in this area in this one regard: where it applies to your own life. Which I guess is another way of saying that what you wrote says more about your outlook on life than on the underlying technology and its social ramifications.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#30

Post by JackFr »

seanmcdirmid wrote: post #20
misterprime wrote: post #5

Earlier quoted context omitted.

From the article: they are planning to do this, and hopeful that it will work. Not actually using it yet.

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.
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