Arguably then the only concrete achievement of quantum computing to date has been improvements to classical algorithms. However, I fully expect that we will eventually have powerful quantum computers.
Practical applications for those are things like modelling chemical reactions or quantum systems, or optimisation.
No discussion on quantum computing would be complete without a link to Scott Aaronson's blog. Worth a read to get a better understanding of the subject.
Even if/when these things are working on a useful scale, quantum computing is going to be more comparable to special-purpose accelerators like GPUs, or perhaps akin having a re-programmable physics lab-on-a-chip. It will be advantageous for the subset of problems that can be cast in the form of Schrodinger's equation, of which there are many. For example, you can use the quantum computer to generate high-fidelity solutions of the electronic structure of some classically intractable molecule, and use those solutions as the training set for a classical AI model that then goes and performs the bulk of the computation on whatever it was you were trying to do.
(IIRC this is still the best; all the hype-y 2^xxx+1 PR ones aren't really using Shor's algorithm and also use some number theoretic short-cuts).
I've worked with analog computers, they were used in control systems. I understand that Moon landing used analog computers along digital ones as well.
Basically you can do PID (proportional, integrative, derivative) calculus on them using plain analog electronics. Very specialized and nothing to get overexcited about.
It's like calling these biological machinery "computers": https://en.wikipedia.org/wiki/File:Human_computers_-_Dryden....
Bottom line "quantum computing" has nothing to do with the classic field of digital computers (personal PCs), it's a stupid, deliberate misuse to borrow from the legitimacy and respectability of an established field.
The term should die in a fire. "quantum crap putting" is a lot more appropriate given all the crap they put in the headlines to fool the guillible.
The general consensus is that there will be a fault tolerant quantum computer by 2035-2040. So like silicon, it is going to take us a while to get there, but we are only talking about 11-16 years or so according to the best experts in the field (remember AI has similar longer terms before it rapidly accelerated).
And quantum computers are profoundly powerful — as in civilization changing computer power.
Then, something I read to the effect that we need to stop thinking of QC as solving classical problems but solving different problems at least reassured me I wasn't too dumb to get it.
Direct answer, QC's are shown to exist at some scale in our universe. They may not get larger than 1000 qbits, but they also might.
However so far the most practical thing that QC has done is inspire new classical algorithms for some problems, notably in recommendation.
QC has led to significant prevention of loss-of-life, loss-of-equipment, and territory gains in battlefield applications. Encrypt/ Decrpyt was already mentioned as a use case. None of these dual-use practical applications are public.
QC is good at "analog" computing: applications where you are more interested in potentials than in 0s and 1s. That lends itself to material design problems. There are applications in battery design and catalytic converter. F1 teams have some interesting fluid dynamics and laminar flow problems where QC was instrumental to test hunches fast. It's not so much about exact compute of solutions, but how to verify a first guess fast to then use traditional software. One could argue this is a niche application, but not if you consider marketing and streaming rights and advertisement impact. A similar approach is used for drug discovery.
None of these "practical" applications are talked about - they are a competitive advantage of commercial enterprises. But if you care for a proxy you could look at any significant hires 1-2 years ago with PhDs, compute, math experience in relevant QC fields. And you would be surprised to see some companies hiring more than 20-30 people in that field (and not just Google or Amazon etc.). That's an FTE expense that could just be hedging of a large company; but could also be product design; and is definitely more than a test balloon or R&D pet project. Some of these companies are known for industrial adhesives, specialty cement, or "green" base oils for lubrication and cooling and cutting. so not all tech companies or big pharma.
But then again I'd say that it doesn't need to.
From a theoretical perspective QC improves our understanding of the physics of computation by bridging the gap between our classical theories of computation and our quantum theories of physics.
QC gives us access to "quantum observers" to allow us to take our understanding of what Quantum Physics "means" further.
QC lends some support to the many-worlds interpretation of Quantum Physics - Where else is the computation being done if we are retrieving answers from their interferences?
From a physical perspective we are learning a lot tackling the hard challenges of realizing them.
Even if we never build "practical" Quantum Computers, experimentally it would still be worth building them as physics experiments.
And if we can build real practical machines they might have significant advantages in some practical fields like quantum physics simulations.
* Unless somewhere the NSA (or their Chinese equivalent) are breaking cryptography using some moonshot machine.
https://spectrum.ieee.org/quantum-computing-skeptics
Related HN discussion
"Scott’s Supreme Quantum Supremacy FAQ" (2019) https://news.ycombinator.com/item?id=21053405 https://www.scottaaronson.com/blog/?p=4317
/? quantum supremacy 2024: https://www.google.com/search?q=quantum+supremacy+2024
/? practical quantum advantage: https://www.google.com/search?q=quantum+advantage
a) just barely exited the era of theoretics-only (19th century, Babbage)
b) just barely entered era of analogue devices-only (1900s, beginning of vacuum lamps)
c) still a decade away from barely practical computers (1940s, Turing and germans)
if you want to learn "what will be practical once usable quantum computer appears", look at https://quantumalgorithmzoo.org/
Even if QC hasn't achieved anything tangible yet, the side effects of it looming are pushing things on.
However there are scientific scenarios where superpositions and qubits come into play. They can also decrypt any form cryptology faster than any conventional computer system. The problem is that they are not as energy efficient as a conventional system.
besides that, it's mostly quackery by pretending code to impossible low temperature calibration and sensors don't exist.
Where it’ll be under active development for 50+ years, without any major application.
Then “ChatGPT” will come along and be the big unlock for its area.
