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After 20 years in VLSI, I have no clue about quantum computers, and haven't found a good source explaining them. Anyone have any idea how they work? Like, how

After 20 years in VLSI, I have no clue about quantum computers, and haven't found a good source explaining them. Anyone have any idea how they work? Like, how does one produce logic gates out of them? How do you create an IEEE 754 Floating point multiplier? I get that they're supposed to represent overlaid states on the same device due to Pauli exclusion, but how do you separate out states and use them in logic? Or save states? What happens if logic produces the same state for one device? Is standard metal used to send signals, or is it something fancy-dancy like neutrinos? It's honestly the most exotic thing I know of in tech, just trying to even begin to get a handle on it, never-mind trying to perform useful work out of them.

StringyBob 9y ago
I've only progressed this far: https://www.smbc-comics.com/comic/the-talk-3 https://www.smbc-comics.com/comic/the-talk-3
heavenlyblue 9y ago
You are not supposed to reproduce classical systems on a quantum computer just the same way you're not supposed to reproduce electric circuits on a classical computer, even though it's made out of them. For me myself one of the easiest concepts to understand was quantum annealing (https://en.wikipedia.org/wiki/Quantum_annealing https://en.wikipedia.org/wiki/Quantum_annealing). It does not mean that's the strongest point of quantum computers, but it's a nice way to start.
- alanbernstein 9y ago
  I get where you're coming from with that analogy, but there is probably a better way to put it. Circuit simulation is a long-time application of computers (https://en.wikipedia.org/wiki/SPICE https://en.wikipedia.org/wiki/SPICE).
  - heavenlyblue 9y ago
    You're down the Turing machine rabbit hole - I implied you could do that. Just the same way you could simulate a processor using an another processor - it's just not as efficient. By the way - you could as well simulate a quantum computer on a classical computer; it'd just be incredibly slow.
phasecode 9y ago
This might be a bit too basic but Kurzgesagt has a great video on Quantum Computers (at https://www.youtube.com/watch?v=JhHMJCUmq28 https://www.youtube.com/watch?v=JhHMJCUmq28).
sp332 9y ago
There are lots of different ways to build a quantum computer, so you might get conflicting answers about the materials and signaling mechanisms. But what they have in common is that they are probabilistic, and there are very few algorithms that take advantage of this to speed things up instead of just adding noise. Shor's algorithm for factoring numbers and Grover's search algorithm work by constructive and destructive interference of the wavefunctions of entangled particles, amplifying the probabilities of the right answers. http://twistedoakstudios.com/blog/Post2644_grovers-quantum-search-algorithm http://twistedoakstudios.com/blog/Post2644_grovers-quantum-s... http://algassert.com/post/1718 http://algassert.com/post/1718
rhn_mk1 9y ago
Quantum computations are a case of reversible computations. If you're aiming to relate qantum computers to other kinds of computers, I suggest starting with the paper called "Synthesis and Optimization of Reversible Circuits - A Survey" [0] It describes the kinds of computations that need reversible computations and kinds of devices that can perform them. That makes it easier to notice similarities, as quantum computers are not the only ones in this category. Notably, photonic and low power computations call for reversibility. The first couple of pages of the paper also touch upon what can be done with them - while you don't have to throw away all you knew about logic gates, the reversible ones are their own thing. If the water goes too deep, perhaps Mika Hirvensalo's "Quantum computing" helps. It approaches the topics of how to compute with qubits from mathematical side. I still don't know the theory behind quantum annealing though - I don't think these two cover it. Still, I learned that the main difference is that the state doesn't have to travel as with electronic circuits, but rather one would likely "apply" gates as "events" acting on the state. A qubit could then be any quantum object - a electron trapped in one place and being hit with photons for example. Place a couple together and hit them in a coordinated way and that event was your gate. When it comes to saving states, it will be problematic. Of course, it's possible to "save" a qubit to another qubit - with some workarounds for the "no-cloning" principle. But if you mean saving them to a classical system, it seems it's not possible at all. A qubit is a representation of a probability, and once read it's destroyed. You could try recalculating it several times and get an idea of the probability it represents. However, qubit readouts are not guaranteed to be independent from one another, giving another bit of headache here. Disclaimer: I'm not a physicist - just a software engineer trying to understand the hype. [0] https://arxiv.org/abs/1110.2574 https://arxiv.org/abs/1110.2574
exabrial 9y ago
Ask you shall receive. Total these videos are about 30m but they're designed for someone that has taken Intro to Computer Engineering and Intro to Logic. * https://www.youtube.com/watch?v=F8U1d2Hqark https://www.youtube.com/watch?v=F8U1d2Hqark * https://www.youtube.com/watch?v=ZoT82NDpcvQ https://www.youtube.com/watch?v=ZoT82NDpcvQ

StringyBob 9y ago

I've only progressed this far: https://www.smbc-comics.com/comic/the-talk-3 https://www.smbc-comics.com/comic/the-talk-3

heavenlyblue 9y ago

You are not supposed to reproduce classical systems on a quantum computer just the same way you're not supposed to reproduce electric circuits on a classical computer, even though it's made out of them. For me myself one of the easiest concepts to understand was quantum annealing (https://en.wikipedia.org/wiki/Quantum_annealing https://en.wikipedia.org/wiki/Quantum_annealing). It does not mean that's the strongest point of quantum computers, but it's a nice way to start.

alanbernstein 9y ago
I get where you're coming from with that analogy, but there is probably a better way to put it. Circuit simulation is a long-time application of computers (https://en.wikipedia.org/wiki/SPICE https://en.wikipedia.org/wiki/SPICE).
- heavenlyblue 9y ago
  You're down the Turing machine rabbit hole - I implied you could do that. Just the same way you could simulate a processor using an another processor - it's just not as efficient. By the way - you could as well simulate a quantum computer on a classical computer; it'd just be incredibly slow.

phasecode 9y ago

This might be a bit too basic but Kurzgesagt has a great video on Quantum Computers (at https://www.youtube.com/watch?v=JhHMJCUmq28 https://www.youtube.com/watch?v=JhHMJCUmq28).

sp332 9y ago

There are lots of different ways to build a quantum computer, so you might get conflicting answers about the materials and signaling mechanisms. But what they have in common is that they are probabilistic, and there are very few algorithms that take advantage of this to speed things up instead of just adding noise. Shor's algorithm for factoring numbers and Grover's search algorithm work by constructive and destructive interference of the wavefunctions of entangled particles, amplifying the probabilities of the right answers. http://twistedoakstudios.com/blog/Post2644_grovers-quantum-search-algorithm http://twistedoakstudios.com/blog/Post2644_grovers-quantum-s... http://algassert.com/post/1718 http://algassert.com/post/1718

rhn_mk1 9y ago

Quantum computations are a case of reversible computations. If you're aiming to relate qantum computers to other kinds of computers, I suggest starting with the paper called "Synthesis and Optimization of Reversible Circuits - A Survey" [0] It describes the kinds of computations that need reversible computations and kinds of devices that can perform them. That makes it easier to notice similarities, as quantum computers are not the only ones in this category. Notably, photonic and low power computations call for reversibility. The first couple of pages of the paper also touch upon what can be done with them - while you don't have to throw away all you knew about logic gates, the reversible ones are their own thing. If the water goes too deep, perhaps Mika Hirvensalo's "Quantum computing" helps. It approaches the topics of how to compute with qubits from mathematical side. I still don't know the theory behind quantum annealing though - I don't think these two cover it. Still, I learned that the main difference is that the state doesn't have to travel as with electronic circuits, but rather one would likely "apply" gates as "events" acting on the state. A qubit could then be any quantum object - a electron trapped in one place and being hit with photons for example. Place a couple together and hit them in a coordinated way and that event was your gate. When it comes to saving states, it will be problematic. Of course, it's possible to "save" a qubit to another qubit - with some workarounds for the "no-cloning" principle. But if you mean saving them to a classical system, it seems it's not possible at all. A qubit is a representation of a probability, and once read it's destroyed. You could try recalculating it several times and get an idea of the probability it represents. However, qubit readouts are not guaranteed to be independent from one another, giving another bit of headache here. Disclaimer: I'm not a physicist - just a software engineer trying to understand the hype. [0] https://arxiv.org/abs/1110.2574 https://arxiv.org/abs/1110.2574

exabrial 9y ago

Ask you shall receive. Total these videos are about 30m but they're designed for someone that has taken Intro to Computer Engineering and Intro to Logic. * https://www.youtube.com/watch?v=F8U1d2Hqark https://www.youtube.com/watch?v=F8U1d2Hqark * https://www.youtube.com/watch?v=ZoT82NDpcvQ https://www.youtube.com/watch?v=ZoT82NDpcvQ