What interesting computation can you do on a 16 qubit processor?
you could factor an 8 bit number really fast heh
I think it's more like a 6 bit number, and probably not very fast at all...
Q – Initiative to build commercially available universal quantum computers
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Re: Q – Initiative to build commercially available universal quantum computers
#5216 qubits? How hard is it to simulate those 16 qubits with a regular computer? I get this is marketing but people would be better off just running a simulator at this point.
It's pretty easy. If your computer has enough ram to store a size 2^16 length complex vector (which is 2^20 bytes, or 1MB) than you can open up an ipython notebook and write code to apply quantum gates to it with no problem.
The problems start to set in if your RAM can't hold the wavefunction in memory (so around 28 qubits, which takes 2^32 bytes = 4GB of RAM.)
With specialized code and supercomputers you can get a little farther, but you will be fighting exponential growth, so not too much. The practical limit for classical computers is in the 40-50 qubit range.
Re: Q – Initiative to build commercially available universal quantum computers
#5316 qubits? How hard is it to simulate those 16 qubits with a regular computer? I get this is marketing but people would be better off just running a simulator at this point.
With 16 qubits, the Hilbert space has 2^16 = 65536 elements. For numerical simulation, you need to store the wavefunction amplitude for each of these elements, usually using a double-precision complex number (16 bytes). Altogether the wavefunction can be stored as a vector with 1 MiB of data. AFAIK all quantum computing algorithms can be expressed as a sequence of 1- and 2-qubit operations, which would be implemented as sparse matrix-vector products. So the simulation part is almost trivial. ;) I'd say that for 16 qubits, designing the quantum circuit to perform an actually useful operation is the far more difficult part.
However, once you start adding more qubits the simulation part becomes hard to infeasible. I think I saw some paper which simulated around 40 qubits. Here the wavefunction already needs 16 TiB, so you need a big HPC cluster to run that.
Re: Q – Initiative to build commercially available universal quantum computers
#54The point where it gets interesting for realistic physics and chemistry applications is around 100 (error-corrected) logical qubits and 10^8 coherent operations, see for example https://arxiv.org/abs/1510.03859 . The error correction adds another factor of at least 100 or so in both qubits and gates needed (but possibly much bigger than 100, depending on qubit quality), see for example https://arxiv.org/abs/1312.2316…
Don't forget cryptography.
Re: Q – Initiative to build commercially available universal quantum computers
#55The point where it gets interesting for realistic physics and chemistry applications is around 100 (error-corrected) logical qubits and 10^8 coherent operations, see for example https://arxiv.org/abs/1510.03859 . The error correction adds another factor of at least 100 or so in both qubits and gates needed (but possibly much bigger than 100, depending on qubit quality), see for example https://arxiv.org/abs/1312.2316…
Don't forget cryptography.
That's covered by "factoring large integers", I do believe.
Re: Q – Initiative to build commercially available universal quantum computers
#56Earlier quoted context omitted.
My point is that QC-s have the potential to be as revolitonary as transistors were. Yet we are at the level when transistors were mostly used to make radios portable. Thus it's not really justified to mock them as lame factoring devices.
That's not how I read your comment. It clearly tries to suggest that when the transistor was first invented people did not know what to do with it. I think the MASER/LASER would have been a far better example.
Perhaps a Leyden jar, or Aeolipyle. Novelties with great potential. Or perhaps, they're just a drinking bird kind of novelty - i don't think so, but maybe. QM is rock solid, but it doesn't tie together well with our other theories about the world. Maybe knowing more will make the error correction easier somehow.
I kinda think we're in the difference engine phase of quantum computing. Same problems as Babbage building a neat thing, but we're missing some details and our tools aren't really sharp enough to make a good one.
Re: Q – Initiative to build commercially available universal quantum computers
#57Earlier quoted context omitted.
> but the service won't be valuable if the computer doesn't work. So the state-of-the-art in quantum computing is still basically "can tell you the 200th prime number, sometimes"? Not very useful.
But this is new territory, and researchers shouldn't give up just because it doesn't work very well now. I recall that the iPhone/iPad were preceded by attempts at tablet computing that were very crude in comparison. Give it a couple of years and see where it leads.
The current state of the art in QC is more like Alan Kay's Dynabook paper: https://en.wikipedia.org/wiki/Dynabook
i.e. even the "very crude attempts" stage (your Newtons or Palm Pilots) is still science fiction.
Re: Q – Initiative to build commercially available universal quantum computers
#5816 qubits? How hard is it to simulate those 16 qubits with a regular computer? I get this is marketing but people would be better off just running a simulator at this point.
It's pretty easy. If your computer has enough ram to store a size 2^16 length complex vector (which is 2^20 bytes, or 1MB) than you can open up an ipython notebook and write code to apply quantum gates to it with no problem. The problems start to set in if your RAM can't hold the wavefunction in memory (so around 28 qubits, which takes 2^32 bytes = 4GB of RAM.) With specialized code and supercomputers you can get a l…
> If your computer has enough ram to store a size 2^16 length complex vector (which is 2^20 bytes, or 1MB)
One megabyte was enough even for quantum computing! Wow. Bill Gates, what a visionary ;-)
Re: Q – Initiative to build commercially available universal quantum computers
#59Looking at the SDK, the programming language of the future is Python.
Re: Q – Initiative to build commercially available universal quantum computers
#60Earlier quoted context omitted.
Are you suggesting IBM is not profitable?
They seem to be running on inertia at this point. I haven't seen any plausible new enterprises from them. It's possible I'm looking in the wrong places, though.
Fully agreed, but they've been running on inertia for the last two decades, but that has nothing to do with profitability. They're still printing money, every quarter and are paying out substantial dividends.
Obviously that can't go on forever and they're desperately searching for a path to a viable future but for the moment they are definitely in the black and will - as far as I can see - stay there for quite a while to come.