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Chinese Researchers Achieve Quantum Entanglement Record

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Re: Chinese Researchers Achieve Quantum Entanglement Record

#111

Post by bscphil »

deepGem wrote: post #23
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?

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…

This is probably a dumb question, but could you spread out the error correction in time? I know it's hard to create very large entangled systems, so would it be possible/easier to do the calculation with 4000 real qubits 1000 times and use the repetition for error correction? (Checking for correct factorization is easy, after all.)

Re: Chinese Researchers Achieve Quantum Entanglement Record

#112

Post by bdamm »

stouset wrote: post #100
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 explanation you're supposing for the "spooky action at a distance" is called a hidden variable theory, and as others have said, this explanation has been disproven. You might be wondering how , and I'll tell you the scenario (adapted from The Elegant Universe) that helped me understand. Imagine you and I each have a device: a small box with one openable window on the top, one on the front, and one on the back. Wh…

What I draw from this is that polarized light doesn't quite work the way we think, and the investigation should be into the modes of polarity.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#113

Post by danbruc »

breadAndWater wrote: post #110
danbruc wrote: post #109

Earlier quoted context omitted.

If you read through the list of Bell test experiments [1], you will discover that not all of them are done with photons, for example »Violation of Bell’s inequality in Josephson phase qubits« [2]. [1] https://en.wikipedia.org/wiki/Bell_test_experiments#Notable_... [2] https://web.physics.ucsb.edu/~martinisgroup/papers/Ansmann20...

https://en.wikipedia.org/wiki/Inconsistent_comparison Josephson phase qubits aren't even utilizing the same fundamental concepts to examine the qualities of the mediums that quantum uncertainty affects. https://en.wikipedia.org/wiki/Phase_qubit https://en.wikipedia.org/wiki/Josephson_effect https://en.wikipedia.org/wiki/Josephson_voltage_standard

You complained - without providing any substantive arguments why this might be an issue - that all Bell test experiments use polarizers, I pointed out that you are wrong. I have no idea what you are complaining about now, what is »[...] qualities of the mediums that quantum uncertainty affects [...]« even supposed to mean? You are obviously far outside of your area of competence. If not, just do the experiment, write the paper, and collect your Nobel Prize, no need to argue with clueless people on the web.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#114

Post by renox »

Filligree wrote: post #64
madeuptempacct wrote: post #47

Earlier quoted context omitted.

Thanks, this helps a lot, but just to clarify: Originally "We 'shine' a bunch of photons at an object, and see if they come back. Except there could be dragged decoy spamming photons back at us, and we don't know if there is. Or it could be sending out so much light, our photons coming back are lost in the mix." With quantum: "We can verify that any photons that get reflected are the ones that we sent out and check o…

Right. Oversimplifying a lot, it's putting a name tag on the photons. Then you can sort out the tagged ones from all the others, drastically reducing the practical noise floor.

Except that photons don't have tags.. Each time a story talk about entanglement, I'm stuck: what does it mean experimentally to verify that two particles are entangled? I don't know..

Re: Chinese Researchers Achieve Quantum Entanglement Record

#115

Post by simcop2387 »

bscphil wrote: post #111
deepGem wrote: post #23

Earlier quoted context omitted.

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…

This is probably a dumb question, but could you spread out the error correction in time? I know it's hard to create very large entangled systems, so would it be possible/easier to do the calculation with 4000 real qubits 1000 times and use the repetition for error correction? (Checking for correct factorization is easy, after all.)

That's been one strategy I've seen mentioned in regards to Shor's algorithm many times. Since there's the probability of an error, you still have to check it and rerun it a few times until you confirm the right answer.

That's still many times faster than you'd get conventionally, so it's a reasonable trade off.

But it doesn't address the possibility that you can't entangle enough qubits to begin with, or keep them stable long enough to actually perform the calculations, which is where the error correction stuff comes in. I don't know enough about the challenges there to comment on how many you'd need (though 1000:1 seems high to my naive intuition, i'd guess maybe 10-100 for magnitude myself).

Re: Chinese Researchers Achieve Quantum Entanglement Record

#116

Post by p1necone »

Erlich_Bachman wrote: post #97
jblow wrote: post #79

Earlier quoted context omitted.

I disagree. The slowness of these languages is mostly uncorrelated with increases in productivity. People only think there’s cause-and-effect here because they haven’t seen counterexamples, because the trend in language design for 25 years has been to make slow languages.

They haven't seen counterexamples because there are virtually none. If what you said was correct wouldn't there be many examples of big bodies of code written in a language like C? (And you can't say "linux kernel" - low-level code needs to be written in a low-level language, in order to communicate with the lower levels like hardware and controllers and such. There is a practical reason to write that in C.) > becaus…

I think the point that the comment you're replying to is trying to make is not that big complicated software engineering can be done in say, C with similar levels of productivity to say, Java.

He's instead saying that it's very much possible to build a language with a similar level of abstraction/ergonomics to say, Java, or Python, or C#, or whatever but with similar performance characteristics to a lower level language like C. And we are starting to see this - there are languages like Rust or D which are (at least to my eyes) much less arduous and foot-gun prone than languages like C or C++ while having similar (or better) performance.

Of course there's also Jai, but I think we should remain unbiased here :P

As an aside though - I think some of those orders of magnitude of performance gains could be had by just writing better code in your existing high level languages. (At least in my experience with enterprise software dev).

Re: Chinese Researchers Achieve Quantum Entanglement Record

#117

Post by donutte »

breadAndWater wrote: post #110
danbruc wrote: post #109

Earlier quoted context omitted.

If you read through the list of Bell test experiments [1], you will discover that not all of them are done with photons, for example »Violation of Bell’s inequality in Josephson phase qubits« [2]. [1] https://en.wikipedia.org/wiki/Bell_test_experiments#Notable_... [2] https://web.physics.ucsb.edu/~martinisgroup/papers/Ansmann20...

https://en.wikipedia.org/wiki/Inconsistent_comparison Josephson phase qubits aren't even utilizing the same fundamental concepts to examine the qualities of the mediums that quantum uncertainty affects. https://en.wikipedia.org/wiki/Phase_qubit https://en.wikipedia.org/wiki/Josephson_effect https://en.wikipedia.org/wiki/Josephson_voltage_standard

Just to be clear, these are experimental results that are statistically impossible assuming a classical physics. Are you actually worried that they are somehow studying the wrong self-evidently non-classical thing, or what?

Re: Chinese Researchers Achieve Quantum Entanglement Record

#118

Post by mike00632 »

madeuptempacct wrote: post #33
downrightmike wrote: post #2

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?

Think of the quantum state as another measurement to make on the incoming signals. The receiver already measures many characteristics of incoming waves, like frequency and amplitude, and now it has yet another measurement that can be helpful. It's helpful specifically because they kept a reference wave with the same quantum state. With more data you can get higher fidelity which means you can perhaps see further or see the same distance with less power.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#119

Post by mike00632 »

barbegal wrote: post #7
downrightmike wrote: post #2

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...

I understand the core concept of quantum radar but does it actually work in practice as a radar? i.e. you can resolve targets with a small range and angular resolution.

Theoretically you would combine the new tech with the old tech. Quantum state would be another measurement to make on the incoming wave on top of measurements like frequency and amplitude.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#120

Post by [deleted] »

jblow wrote: post #79
ams6110 wrote: post #57

Earlier quoted context omitted.

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…

I disagree. The slowness of these languages is mostly uncorrelated with increases in productivity. People only think there’s cause-and-effect here because they haven’t seen counterexamples, because the trend in language design for 25 years has been to make slow languages.

[deleted]
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