Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Chinese Researchers Achieve Quantum Entanglement Record

scientificamerican.com

Post reply on HN
Print view View original

141–150 of 152 posts

Re: Chinese Researchers Achieve Quantum Entanglement Record

#141

Post by breadAndWater »

donutte wrote: post #132
breadAndWater wrote: post #130

Earlier quoted context omitted.

Uh, wow, at no point have I made the claim that an electrical circuit is not a quantum system. Nor have I claimed that they are incapable of simulating quantum phenomena. Quite the very opposite. What I did clearly state, and insist as quite relevant, is that entanglement and double slit experiments are hocus pocus and irrelevant distractions. In fact, I stated that this experiment says basically nothing because it m…

The experiment demonstrates quantum entanglement. I gather you don’t believe this. So how about this: I don’t believe you. I don’t believe that you could, even theoretically , produce the data from a loophole-free Bell test without invoking superdeterminism, superluminality, or quantum entanglement. Can you describe how this would be theoretically possible?

The experiment certainly demonstrates "something" in terms of how not to "measure" relativistic effects with macroscopic tools...

And yet, with relativistic particles, the wild claims are made that splitting photons through a substrate, and then passing them through the wall of a polarizing lens, means we can declare ourselves capable of rewriting and erasing history. Eh, not quite.

But hey, where there's smoke, there's fire, so something must be true, right? Let's just make up whatever.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#142

Post by sir_kin »

rurban wrote: post #103
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?

2048 would break current crypto, >20 would help solving most unsolvable NP hard problems.

2018 LOGICAL qubits would break current crypto. But qubits decohere extremely fast, so you need error correcting schemes. Current estimates require 1000 - 10000 physical qubits per logical error corrected qubit.

[1] https://en.wikipedia.org/wiki/Quantum_threshold_theorem

Re: Chinese Researchers Achieve Quantum Entanglement Record

#143

Post by sir_kin »

simcop2387 wrote: post #115
bscphil wrote: post #111

Earlier quoted context omitted.

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 st…

For more info on that 1000:1 ratio, see [1].

[1] https://en.wikipedia.org/wiki/Quantum_threshold_theorem

Re: Chinese Researchers Achieve Quantum Entanglement Record

#144

Post by tzakrajs »

whatshisface wrote: post #51
tzakrajs wrote: post #43

Earlier quoted context omitted.

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…

Very insightful, thank you!

Re: Chinese Researchers Achieve Quantum Entanglement Record

#145

Post by moefh »

hrygolis wrote: post #138
moefh wrote: post #89

Earlier quoted context omitted.

> Its suspected P lies entirely within BQP. It's actually known that BQP contains P[1]. It also contains BPP. What's not known is the relationship between BQP and NP (most experts suspect there's no containment in either direction). [1] See this for an easy proof: https://people.eecs.berkeley.edu/~vazirani/f04quantum/notes/...

https://www.quantamagazine.org/finally-a-problem-that-only-q...

That's still only relative to an oracle, though (i.e., BQP^O vs NP^O). We also have oracle separations of P and NP, and that proves nothing about P vs NP without an oracle.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#146

Post by zackmorris »

mundo wrote: post #90
crumpington wrote: post #52

Earlier quoted context omitted.

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…

> There's nothing shocking or spooky about two billiard balls being made to spin in arbitrarily opposing directions, selecting only one, then separating them, and then noticing the spin of one, in order to reliably grasp that the other is the reversal. Okay. So now, make two billiard balls so that they're spinning opposite directions, and separate them to opposite sides of the table. Then, go to ball A and do somethi…

Unfortunately I don't think this is true. The moment you observe them, they are no longer entangled. So they have opposite spin at that point, but if you reverse one, it behaves classically and both electrons then have the same spin.

I'm still trying to wrap my head around why there isn't some hidden variable though which determines which spin they'll have. Like with Bayes' theorum, I keep learning it but for whatever reason my brain won't remember it and I have to look it up again hahah.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#147

Post by aaavl2821 »

cing wrote: post #122
aaavl2821 wrote: post #56

Earlier quoted context omitted.

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

I'm a cofounder of a start-up working on near-term applications of quantum computing in biology, specifically on the protein structure side of things ( https://www.proteinqure.com ). There are many self-contained subproblems in this space which are not limited by data because models are accurate enough to inform experiments, but there's probably not a scientist in the world who would say we have a sufficient understa…

That's interesting, what are some examples of those subproblems?

Re: Chinese Researchers Achieve Quantum Entanglement Record

#148

Post by mundo »

zackmorris wrote: post #146
mundo wrote: post #90

Earlier quoted context omitted.

> There's nothing shocking or spooky about two billiard balls being made to spin in arbitrarily opposing directions, selecting only one, then separating them, and then noticing the spin of one, in order to reliably grasp that the other is the reversal. Okay. So now, make two billiard balls so that they're spinning opposite directions, and separate them to opposite sides of the table. Then, go to ball A and do somethi…

Unfortunately I don't think this is true. The moment you observe them, they are no longer entangled. So they have opposite spin at that point, but if you reverse one, it behaves classically and both electrons then have the same spin. I'm still trying to wrap my head around why there isn't some hidden variable though which determines which spin they'll have. Like with Bayes' theorum, I keep learning it but for whateve…

Correct, this only works if you can reverse the particle's spin without observing it. This is a descriptive example - the real experiment is slightly more complicated - but it was experimentally verified by Alain Aspect in 1982. If you want a more detailed explanation I recommend http://scienceblogs.com/principles/2007/02/22/spooky-action-...

Re: Chinese Researchers Achieve Quantum Entanglement Record

#149

Post by rurban »

sir_kin wrote: post #142
rurban wrote: post #103

Earlier quoted context omitted.

2048 would break current crypto, >20 would help solving most unsolvable NP hard problems.

2018 LOGICAL qubits would break current crypto. But qubits decohere extremely fast, so you need error correcting schemes. Current estimates require 1000 - 10000 physical qubits per logical error corrected qubit. [1] https://en.wikipedia.org/wiki/Quantum_threshold_theorem

No, no one cares about those HW problems. To break RSA keys you need 0 error correction. You only need >2000 entangled qbits, and they either produce a correct result or not.

For other calculations you might need error correction, but this leads to nowhere with current technology. What the Chinese did was groundbreaking.

Re: Chinese Researchers Achieve Quantum Entanglement Record

#150

Post by danbruc »

breadAndWater wrote: post #141
donutte wrote: post #132

Earlier quoted context omitted.

The experiment demonstrates quantum entanglement. I gather you don’t believe this. So how about this: I don’t believe you. I don’t believe that you could, even theoretically , produce the data from a loophole-free Bell test without invoking superdeterminism, superluminality, or quantum entanglement. Can you describe how this would be theoretically possible?

The experiment certainly demonstrates " something " in terms of how not to "measure" relativistic effects with macroscopic tools... And yet, with relativistic particles, the wild claims are made that splitting photons through a substrate, and then passing them through the wall of a polarizing lens, means we can declare ourselves capable of rewriting and erasing history. Eh, not quite. But hey, where there's smoke, th…

1. Do you think all Bell test experiments ever done were flawed, i.e. none of the observed Bell inequality violations were real?

2. If so, do you think a non-flawed Bell test experiment could be done?

3. If so, do you have a definite opinion about whether or not it would yield a Bell inequality violation?

4. If so, would it yield a Bell inequality violation or not.

5. If you think all Bell test experiments ever done were flawed, can you pick one, preferably one commonly considered a good one, and point out what exactly you think the flaw in the experiment is?

6. If you think Bell inequality violations are or could be real, how do you want to explain them?

Note that those are all yes no questions, well, at least all but the last two. I don't need and want more than a yes or no for the first four because from your comments alone it is not clear, at least to me, what your position actually is.

Post reply on HN