171–180 of 215 posts
If it goes well, the history of quantum computing will be divided up in to three eras: the era of twisty philosophical arguments that it's working ("the molecule is simulating itself"), the era of academic arguments that it's working ("we can solve this one carefully constructed problem") and the era of practical arguments ("Amazon is selling QC time for $20/kilogate-bit, what do you mean it's not possible?"). Quantu…
We still don’t know if the third era is possible.
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What are the theoretical models for the energy cost of computing on a qubit? I'll be excited for QC when there is known way (even with some handwaving and future-tech plans) to compute a non-trivial result for a reasonable sum, such as "crack someone's private RSA key for under $10M of compute cost"
> when there is known way (even with some handwaving and future-tech plans) to compute a non-trivial result for a reasonable sum, such as "crack someone's private RSA key for under $10M of compute cost" If you're willing to admit handwaving and future-tech plans, then you can be excited now. It's estimated that a few million physical qubits (corresponding to few thousand logical qubits) will be necessary to crack an…
both of them are very flexible, but also definitively non independent.
I think we need to comes to grips with a hard truth about the reality of academic life. Once you invest decades of your life into a research subject, if it turns out the entire thing is never going to work, there are major social and financial pressures to deceive the public about the true nature of the subject. I saw this happen with string theory first hand, and my experience with string theory was a major factor t…
Yet I have no trouble believing in this quantum supremacy at the current scale.
The way I see it is a quantum computer is "running" an algorithm like Toshiba's "simulated bifurcation". It's running it at a frequency much higher than current computers.
If I had to take a guess it is like running classically at the Bohr frequency of an electron ~10^16 Hz. So it's kind of like trying every combination with some heuristics. Currently we are tapping into this 6 additional order of magnitudes of computation, which allows a brute force search to appear instant. But once we have used this 10^6 speed factor the quantum computer will miss a lot of the solutions and you will have to increase the sampling time exponentially to find your solution. We are currently in the exponential part of the S curve.
You've got to understand that those machines are expensive to build, so putting a cap on the performance won't help you raise funds. But these machines are beautiful. They are some marvel of engineering. There are plenty of things to discover. They need to get built.
They will bring plenty of useful techniques in the how to manipulate and build very small things, and more importantly how to compute without releasing so much heat. But those advances will probably get locked into a few private companies by monopolizing the few big names that can lend the credibility required to raise funds.
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The third stage is the hardest. Thermonuclear energy production has been sitting in "theoretically possible, but economically unviable" for decades, tons of technologies like supersonic commercial flight has been achieved and then scrapped because of practical concerns, many other technologies struggle with passing economic viability barrier. Taking that into account, getting from 2nd to 3rd stage would be the hardes…
Supersonic commercial flight is one of the most interesting. I think two strange things happened. First we got the internet - and mobile phones and video conferences and this has eroded the value of rapid physical presence. Second, and I think this is more important, people have become more willing to sacrifice their time for their career/money/firm/dream vs. family/happiness/now. An acquaintance flew Concorde a lot…
The more comfortable you are in the flight, the less the actual number of hours flown bothers you.
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Supersonic commercial flight is one of the most interesting. I think two strange things happened. First we got the internet - and mobile phones and video conferences and this has eroded the value of rapid physical presence. Second, and I think this is more important, people have become more willing to sacrifice their time for their career/money/firm/dream vs. family/happiness/now. An acquaintance flew Concorde a lot…
Could the improvements in Business and First Class travel, combined with the increased use of private jets (also NetJets) have contributed to the downfall of the Concorde? The more comfortable you are in the flight, the less the actual number of hours flown bothers you.
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Perhaps it will make more sense to explain how a D-Wave machine works, as (a) they actually exist and you can use one today for free online, and (b) it's way simpler than a gate model QC is. Imagine a bunch of magnets. Imagine forcing them into a "frustrated" configuration; maybe you have them all on a grid, and you have servomotors that can rotate them to face any way you like. The servomotors are strong, so counter…
> Now, if you can map some useful computational question onto the original configuration of qubits that is answered by the ending position, you've got yourself a useful quantum computer. This is the hard part! Yes, I agree. But this has not been demonstrated. What's being demonstrated (apparently) is that measuring a quote-unquote "quantum computer" doing whatever it does naturally is easier than simulating said quan…
The experiment used a classical computer to randomly generate a circuit C, told the quantum computer to execute it, and recorded the result. Then they repeated this but executed each circuit in the most optimal way a classical computer can. Finally they compared the distributions to verify that the quantum computer's results matched the correct classically computed results.
This proves that the quantum computer is able to generate that distribution faster than a classical computer and isn't just doing some other spurious process that happens to be faster.
Yes, this random distribution isn't very useful and so this result is only really interesting as an experimental verification of theory. However, it is a computation that benefits from quantum speedup in real life!
Hopefully soon, algorithms will be found to generate more useful distributions (as it seems for the time being sampling is the only application of this type of QC that is practically doable). For example, Aaronson mentions that generating verifiably random bits is not much more difficult than the noise generated in this experiment and could have an impact in a variety of cryptographic applications.
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Supersonic commercial flight is one of the most interesting. I think two strange things happened. First we got the internet - and mobile phones and video conferences and this has eroded the value of rapid physical presence. Second, and I think this is more important, people have become more willing to sacrifice their time for their career/money/firm/dream vs. family/happiness/now. An acquaintance flew Concorde a lot…
Could the improvements in Business and First Class travel, combined with the increased use of private jets (also NetJets) have contributed to the downfall of the Concorde? The more comfortable you are in the flight, the less the actual number of hours flown bothers you.
No amount of money makes getting from your front door to the airport not be a massive pain potentially taking over an hour if you have some bad luck
Preface: I know nothing about quantum computing. What exactly is a qubit? I'm not asking what does it mean, because I know there's superpositions and all that jazz, but as in...like, in an electronic circuit, what is a qubit? Is it made out of logic gates? Which ones? If we can make one qubit, can't we just make a bunch of them by copy and pasting circuits similar to how we used vacuum tubes in the 60s and 70s? How c…
Physicists here. In practice, a qubit is a two-level physical system. It can be spin state of an electron, polarization of a photon, lowest two energy states of an atom or an electron in quantum dot/well trap potential, the charge state (called charge qubit) -- whether you have 0 or 1 electrons in it, etc etc (if you have 3 levels, it's called qutrit, and for d levels qudit). This experiment uses charge qubits (a spe…
So it looks like QC is good for speeding up simulations, and with far less overhead for ECC and such than it needs for things like factoring. So is simulation the QC "killer app"? Does it only do certain kinds of simulations well, i.e. simulations of quantum systems, or can that be generalized? Can it be applied to economic, environmental, traffic, etc as well?
>Can it be applied to economic, environmental, traffic, etc as well? Our current understanding is that quantum computers won't offer a speedup for the simulation of nonquantum systems. The only simulations they'll be faster for are systems for which quantum effects are important. Of course it's possible that someone will discover an algorithm that gives quantum computers an exponential speedup in the simulation of an…
The speedup from grover's algorithm is essentially universal it's just not an exponential speedup. So for example in your non-quantum simulation task, you want to search for an input to a cellular automata that makes it spell your name after 5000 timestemps. You can use grover's algorithm to find that input with a sqrt() the number of simulation runs that a classical machine would need (and perhaps fewer, since there are likely multiple solutions).
To me that's one of the most interesting things about quantum computation: There is a very broad class of things where it offers a modest speedup (sqrt) and a narrow (but useful!) class of things where it offers an exponential speedup. But if you imagine almost any kind of 'superpowered quantum computation'-- something that is a little more powerful than the laws of physics as we know them allow-- you almost always get an exponential speedup for everything (or even more absurd results, like every problem being solvable in constant time). QC has this interesting property of being just strictly more powerful than classical computing, but without being magic-instant-computing.
[Which is also why many of the common incorrect descriptions of quantum computing are sad, stuff like "testing all values in paralle"-- if it worked like that description it would be magic instant computing.]
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I agree on your other points and trust that you are more qualified to judge what the biggest obstacles are. Do you have a paper I can look into that goes into the chip architectures in more detail (not specifically for this new device)? Otherwise I'll await the science / nature paper of this demonstration. The classical circuit is mostly outside the cryo I assume since it's GHz's and LNAs are available. Do you know i…
When you say chip architecture, I assume you mean how to assemble together qubits like an integrated circuit. Here's one proposal for silicon based qubits: https://www.nature.com/articles/s41467-017-01905-6 Microwave signals are typically used for control rather than readout. I don't know if this experiment does it or not, and I am not an experimentalist. Multiplexing is more typically required for reducing timing er…