11,330 karma · joined May 1, 2009
"Manipulating" yes, that is the whole point. But you don't measure all those astronomical number of variables. The measurements stay sane, the state does not.
> it deserves something more thoughtful than a dismissive response
To me this article is itself a dismissive response to quantum computing.
It is totally reasonable to predict a quantum computing winter, but all the supporting arguments here seem to be about how "hard-headed engineers" know best.
> So the number of continuous parameters describing the state of such a useful quantum computer at any given moment must be at least 2^1000, which is to say about 10^300. That’s a very big number indeed.
Yes this is the whole point: if it wasn't this big, we could just simulate it on a regular computer.
> To repeat: A useful quantum computer needs to process a set of continuous parameters that is larger than the number of subatomic particles in the observable universe.
Yep.
> it’s absolutely unimaginable how to keep errors under control for the 10^300 continuous parameters that must be processed by a useful quantum computer.
I do imagine it, every day. But I'm a professional, so maybe that doesn't count?
> How many physical qubits would be required for each logical qubit? No one really knows...
There are plenty of such estimates around. Obviously it depends on the noise rate of each qubit.
> all of the assumptions that theorists make about the preparation of qubits into a given state, the operation of the quantum gates, the reliability of the measurements, and so forth, cannot be fulfilled exactly. They can only be approached with some limited precision. So, the real question is: What precision is required? ... Amazingly, not only are there no clear answers to these crucial questions, but they were never even discussed!
There are boatloads of papers (and conferences) that discuss exactly this. Obviously it is a vital question to answer!
My advice is to find a teacher. If they are any good they will speed up the process by one or two (or more) orders of magnitude. Even the professionals do this.
related HN discussion: https://news.ycombinator.com/item?id=15372856
Try to find someone you can talk to, and work with, that doesn't make you feel stupid. You seem to be focusing too much on the "I": it makes a huge difference the relationships you form. Huge.
This could be difficult for you, but here's another idea: be vulnerable. Let people know what's going on with you, that you're afraid and need a leg-up. Being vulnerable in this way is actually a sign of great strength. Your post here on HN is already a step in this direction.
This is so true: playing Go strips you naked, everything about your personality comes out in the game. It's completely terrifying. And awesome.
http://www.feynmanlectures.caltech.edu/III_toc.html
You might also like John Bell's original papers. Feynman doesn't do entanglement. Conway's "free will" paper is good aswell.
Check out the breezy writing in this paper: https://arxiv.org/abs/1602.07618
Also, the Rosetta stone paper (more advanced): https://arxiv.org/abs/0903.0340
I don't agree with this. Quantum measurements are projective and they are very much one way. People seem to want to dismiss this as being just "epistemic" like the way entropy (thermodynamics) is one-way, but not fundamentally one way. Entropy increases only because we can't see all the details. Quantum measurements are not like that.
I don't think there is any inherent reason why this would have to be done using "specialized communications hardware and cables". Didn't the Chinese just demonstrate entanglement sharing via satellite?
I could imagine a post-quantum computing era where it is even possible to know, with certainty, if you have been hacked, or data breached, because of quantum cryptography. We are not any where near this kind of technology right now, but the physics is real.
If something even slightly goes wrong with my software I don't want it to survive at all. This is the equivalent of putting dynamite on all the load bearing points of a structure, rigged to explode if they move out of place!
Software doesn't bend, it's digital.
This is not unitary. Quantum theory has two parts: unitary evolution, and measurement processes. That's it.
I don't think so.
> "piles of words"
I definitely agree about the piles. Maybe ordinary language is just to feeble for this stuff.
<u|U^\dag U|v> = <u|v>.
The basic problem with your suggestion is that it does not explain how anything actually "happens". Unitary evolution is a theory where nothing changes. People seem to think that they can evoke decoherence, or similar, and these issues disappear. But they do not.
Anyway, I'm not positing any solution, I am just saying that it irks me that all these ideas are dismissed whenever it comes to the problem of the asymmetry of time. It just seems bizarre to me.
This is the bit that irks me. Quantum mechanics, the real QM that physicists actually use, involves collapse of the wavefunction. This is absolutely time-asymmetric. But in all these discussions of "why is time one-way?" this never seems to be mentioned. Apparently QM is not a real theory, and just a placeholder until we can work something out properly. Irk!
Here is the money quote for me:
"Were his readers not reading well enough, or did he not write it well enough? Disagreement is mostly blamed on miscommunication. The burden of clarity is now entirely on the author, which makes for dull and repetitive arguments — and a demand that certain people come to represent, unambiguously, certain arguments. One’s cards must all be laid on the table, faceup, and one’s position must be unified. But the rise of misreading doesn’t give permission not to mean what you say."