The need for quantum computers remains small
theregister.com
theregister.com
https://www.newscientist.com/article/2227490-googles-quantum...
Note, it turned out later that classical computers could still do this faster, so, another QC fail.
Water has 8 electrons (which QC can treat exactly without any extra work) in a number of orbital. In general we need 2 qubits per orbital.
Most QC demonstrations so far were performed using so-called minimal basis sets, which have a small number of orbitals and thus give inaccurate results. A better approach would be to take a large orbital basis, do a classical relatively expensive Hartree-Fock calculation then use the orbitals from that to do the QC. This technique when done on classical computers is called MRCI (multi-reference configuration interaction) and is the gold standard in Quantum Chemistry.
So, provided we can pay the cost of doing a large orbital HF calculation (and we can do that for fairly large molecules), we can get pretty good result using n electrons in n orbitals MRCI. So production electronic calculations of water molecules would take about 16 qubits per molecule.
The more frustrating problem is that the number of electronic interaction terms is N^4 the number of orbitals so that we would very rapidly need extremely deep circuits which are not feasible without error correction (which involve using like 8 actual qubits for every calculation qubit). There are proposal to use plane wave basis sets (N^2 interactions) but then we need many more orbitals and thus many more qubits.
We are in practice very far from QC having a significant impact on real-life quantum chemistry. It's not at all clear that we'll ever be able to do QC on a molecule the size of a typical drug, let alone a protein.
It's true that there could be neat quantum computing shortcuts that maintain calculation accuracy and that aren't doable on classical computers... but then we could also imagine that some neat Quantum Chemistry trick might make classical computers much better too. (We actually have a bunch of these already but they are approximative: DFT, machine learning, pseudo potentials etc.)
Not at very massive scale of investments required.
Take for example, GPGPU (general purpose graphics processing unit). The wast investment needed to get there was funded by gaming industry. Supercomputers as a investment target were tiny compared to gaming and general purpose computing.
AI boom was created on a tails of gaming industry and the benefits spilled into scientific computing as well.
I'm not sure this is something that QC can easily solve.
[0] undergrad ochem is actually a pretty good heuristic for which reactions one can perform at industrial scale, though high scale reactions might require catalysts you don't learn about in ochem
[1] https://scottaaronson.blog/?p=4372from=timeline#comment-1822...
I know Stephen Wolfram isn't too excited. But I believe his issue was more that algorithms end with "and then a measurement happens", which might be quite tricky and possibly even cancel out any potential gains. Not sure about the details of that, but it makes superficial sense given the nature of measurement in QM.
6 SW: Yeah, I think… I think it’s not going to be true[that QC gives a speedup], that’s my guess. I think what’s going to happen is, if you take short algorithm for factoring, which is primarily a quantum Fourier transform, that Fourier transform is done beautifully quickly because there are all these threads that are running in parallel. The problem is, every thread is somewhere in a different place in branchial space, that thread, that us observers, we have to corral all those things back together again in order to tell what actually happened, and that’s… So there’s a… Usually in quantum computing one just says, “and then there’s a measurement.”
1:26:49.0 SW: Now, in actuality, when you have an actual device, you have all kinds of issues in making that measurement, all kinds of… How quickly does it decohere, all these kinds of things. There are all these kinds of very practical experimental features, and I think people have generally said, given the formalism of quantum mechanics, it’s like, well, all this quantum stuff happens and then boom, we do a measurement, and the boom, we do a measurement is actually pretty difficult in practice with actual experiments, that people have said, but if we do these experiments well enough, it will become the mathematical idealization that von Neumann and others made about how measurement works, and I don’t think that’s going to be true. I mean, we’re not sure yet, but it seems likely that there will be no way to do… To sort of, if you’re honest about how the measurement works, the measurement takes effort.
EDIT: I should actually qualify the above, in order to surpass the standard quantum limit we will turn GW detectors into QND (quantum non demolition) detectors using techniques such as frequency dependent squeezing (see Kimble 2000) which is an ideal measurement
I think part of his view is also partially based on the Wolfram Project multiway causal graph framework and its implications on the measurement problem. It's an interesting podcast if nothing else. Not very comprehensible, but interesting nonetheless.
My gut reaction to his mention of a rulial space is to be reminded of the Calabi-Yao manifold situation in string theory. If the space is even close to similar in size to that parameter space, that would be a theoretical nightmare.
Let's assume decoherence won't be a problem.
How about a purely economic perspective. Something like the number of bits of DRAM you can get for the cost of a single qubit. Surely, for quantum computers to become usefulfrom a cost POV, this number needs to shrink, yes?
So it could then be interesting to graph this ratio over time and see where it's headed. My gut is that given the state of the art nature of QC, the cost of 1 qubit should be very high, whereas one bit of DRAM should be very low. Which mean 1 qubit is worth a crazy amount of DRAM.
Does anyone know if this has been analysed?
Or something else.
https://scottlocklin.wordpress.com/2019/01/15/quantum-comput...
The coherent-bits are really not scaling fast enough (and this is to be expected given their entanglement IMO) for anyone to really care other than snazzy startups scamming investors of their money.
From that purview, a general heuristic for approximating combinatorial optimization problems would be a godsent. Even if algorithms like the QAOA do not improve(or tightly match) approximation ratios beyond that of a carefully crafted classical algorithm... A turn key algorithm on a coherent high-qubit-count quantum computer would change the industrial use landscape forever. The number of developer hours saved would be uncountable.
We're just aiming way too dang high.
Nathan Myhrvold, former Microsoft CTO, 1997
Ken Olsen, founder of Digital Equipment Corporation, 1977
Computer revolution was funded by demand in business, gaming and automation. It's the cash flow that funds long term R&D. Not potential benefit.
There is no such demand for quantum computers. Everyday problems have too small complexity for them to be useful even if algorithm exists.
I suspect that computational biochemistry will have funders from drug firms and companies doing materials science to keep funding the research for quantum computing, but the total sum will not be billions per year like it was in computer revolution.
Global supercomputer market is roughly $6-7 billion. Nvidia, AMD together spend more into R&D than the whole market has sales. Scientific use is minuscule compared to business and entertainment needs.
Quantum computers research gets millions or maybe few tens of millions funding. That's not enough.
Last time I checked few years ago, my understanding was the answer was still no; specifically, believe I asked Scott Aaronson as a follow up question to a talk he gave:
We like to imagine that quantum computers will be creating value for society by doing simulations about cutting-edge scientific problems. What if it just lets rich companies impersonate long-dead bitcoin whales?
I also have a very hard time believing that
1) physical reality supports computing with a superposition of 2^{256} states each with an accurate amplitude of magnitude 2^{-128}, and
2) that we can engineer systems preserving such accuracies.
I get that the engineering challenges are hard (or we'd have figured it out by now). And everyone seems pretty bad at predicting how long it will take for us to build something fundamentally new.
But from the physical impossibility side, what would have to be true/what would we learn if we discovered that physical reality _doesn't_ support quantum computation with a large number of qubits and sufficient accuracy?
I did do a course which included some quantum computation material and the professor highlighted that it wasn't actually demonstrated whether nature would be so "extravagant" ... but I haven't heard anyone describe what the universe would need to be like to both support the quantum phenomena that we've already studied and demonstrated, but to disallow some larger/more complex arrangements of what seem to be the same principles.
I'm thinking of some kind of common computational work, with a clearly defined input and verified output, shown to be carried out at least an order of magnitude faster than our conventional computers.
If you can shave off a factor n in O(n^3) then O-B-V-I-O-U-S-L-Y it will change the world. If you don't see the obviousness in this, then why are you working with computers?
Before you hate on me, did you even google "quantum computer"? Did you read the introduction section of the Wikipedia article?
Why? Not every new tech solves a problem people actually have..
At my work, I was present when the research on ASAS (https://skybrary.aero/articles/airborne-separation-assurance...) led to the idea of PMS (https://www.eurocontrol.int/sites/default/files/2021-05/euro...).
Never underestimate serendipity
Oh, come on. Linux was a clone of MINIX with a GPL license. If Linus had not written it, somebody else would have; and at worst (if that is worse), we would have all been running FreeBSD now.
Back then a digital computer couldn’t hold a candle to an analog one and processed only a few bits at a time. It was slow and imprecise. Look at where we are now.
A general quantum computer is a fundamentally different kind of computer. Those who cannot imagine what can be done with one lack the imagination to understand foundationally new technology and are unable to invent their own.
"IBM's current largest quantum computer, revealed this month, contains 65 qubits."
https://www.science.org/content/article/ibm-promises-1000-qu...
These thing are not like your laptop, they are more like particle accelerators.
It's also funnily enough mirrors the everlasting blockchain advocacy.
There's some hypothetical travelling salesperson style questions we might ask. But we don't seem incapable of doing this work today. 98% the needs seem like: can we break the world's crypto. How is this anything beyond a chaotic evil mis-use? How will this do anything but de-secure & instigate risk across the planet?
At least when 99.5% of the engineers were working on ads, they were just wasting their time doing amoral shit. This seems actively immoral.
I really struggle to understand what this all is good for. There probably are some valid & good uses. But it's all hyper-abstract, with little grounding. The attempt to hipster-ize the facilities, to make the physical systems themselves look cool, to present an impressive front: it all works counter to the very essence that made computing cool for so much of my growing-up period: computing in my era was personal. It empowered people. I don't see how this will help actual people at all. It seems mostly like a big hard problem for which the winner reaps some eventual explotative spoils. At likely cost to general world order & peace. Hiss boo.
The advent of SPICE [1] meant that with the right models electrical engineers could simulate complex electrical systems, do sensitivity analysis and make integrated circuits that had a high probability of working.
Imagine a (quantum) simulator that can rapidly simulate all or part of the human body. The effects of medicines could be rapidly simulated, or the simulation could guide the design of treatments. Eventually, if the simulation becomes as accurate as SPICE can be today, it would be possible to go directly from the design of a treatment to its administration, secure in the knowledge that it is unlikely to cause problems.
However, any way you look at it, "[quantum] simulating the human body" is complete batshit science wingnut nonsense (though I tried to be diplomatic about it above). There isn't even any way to measure the input state there! It's ill-defined, it's subject to measurement uncertainty, it's just plain chaotic. As an actual former scientist, it would help my blood pressure if science wingnuts who do not understand the first thing about what they're talking about could please stay quiet.
Defence?
If your secrets (or more likely, your nation's secrets) might be exposed by a quantum attack, then you'd better understand how such an attack might work, so you can defend against it. Nations (some) do research into chemical/biological weapons to learn how to defend against them (purportedly).
That's a "devil's advocate" answer. I lean to the view that, for very big secrets, it's better not to have a secret at all. At least, don't have secrets that need to be kept long-term. That sounds glib and handwavy, and it is; but most secrets seem to get out, sooner rather than later, and usually not as a result of someone cracking the cryptography.
Humanity will never hold hands and sing kumbayah together.
We do not dissuade particle physicists from performing physics because some bad people want atomic bombs; We do not dissuade Archimedes from doing his thing, for the fear of better siege engines;
A have less respect for those hacking the minds of the general public.