3 ms·

We don't need perfectly entangled qubits, but we do need a large number of physical qubits in order to achieve quantum error correction (and in practice get a s

We don't need perfectly entangled qubits, but we do need a large number of physical qubits in order to achieve quantum error correction (and in practice get a smaller amount of perfect logical qubits). We are not very close to that level today, but the progress in the last decade was quite radical.

credit_guy 3y ago
This is really cool, thank you for providing the details. I did a bit of digging, and I think the crucial result that I did not know 25 years ago is the "threshold theorem" [1], which to me sounds like an immensely important result. However, it appears you need quite a bit of noisy cubits, wikipedia mentions 1000 to 10000 for a single logical qubit, but it appears that that's for a level of noise well below what's currently achievable. In any case, quantum n-body problems with tens of entangled electrons are doable with classicla algorithms, so to make an impact you'd need many millions of noisy quantum cubits, maybe even billions. After (admittedly fairly shallow) googling, I found out that IBM plans to have a quantum computer with 100000 noisy cubits ... sometime soon. On the other hand it appears that solid advances happened on the theory side, according to this editorial [2] in the Journal of Chemical Theory and Computation. Still, I can't shake the feeling that it's all just another case of nuclear fusion. When it will happen it will change the world, but that's going to be in 30 years, 30 years from now. [1] https://en.wikipedia.org/wiki/Threshold_theorem https://en.wikipedia.org/wiki/Threshold_theorem [2] https://pubs.acs.org/doi/epdf/10.1021/acs.jctc.3c01043 https://pubs.acs.org/doi/epdf/10.1021/acs.jctc.3c01043
- freetonik 3y ago
  Yup, the threshold theorem is the holy grail. Going back to the number of qubits: IBM and some other research institutes have been working on an idea of connecting multiple quantum computers in a grid. This would potentially help alleviate the problem of "how to fit 1000s of qubits, with all the wiring, into a single fridge", as well as "how to fabricate high-quality single chip reliably". In theory, we could fabricate and wire-up medium sized-chips, setup full quantum computers and connect them with some sort of quantum memory and quantum communication channels. Fabrication is tough; the company I work at does it all, from fabrication of quantum chips to final on-premise installation, and fabrication is as difficult as one can imagine.

credit_guy 3y ago

This is really cool, thank you for providing the details. I did a bit of digging, and I think the crucial result that I did not know 25 years ago is the "threshold theorem" [1], which to me sounds like an immensely important result. However, it appears you need quite a bit of noisy cubits, wikipedia mentions 1000 to 10000 for a single logical qubit, but it appears that that's for a level of noise well below what's currently achievable. In any case, quantum n-body problems with tens of entangled electrons are doable with classicla algorithms, so to make an impact you'd need many millions of noisy quantum cubits, maybe even billions. After (admittedly fairly shallow) googling, I found out that IBM plans to have a quantum computer with 100000 noisy cubits ... sometime soon. On the other hand it appears that solid advances happened on the theory side, according to this editorial [2] in the Journal of Chemical Theory and Computation. Still, I can't shake the feeling that it's all just another case of nuclear fusion. When it will happen it will change the world, but that's going to be in 30 years, 30 years from now. [1] https://en.wikipedia.org/wiki/Threshold_theorem https://en.wikipedia.org/wiki/Threshold_theorem [2] https://pubs.acs.org/doi/epdf/10.1021/acs.jctc.3c01043 https://pubs.acs.org/doi/epdf/10.1021/acs.jctc.3c01043

freetonik 3y ago
Yup, the threshold theorem is the holy grail. Going back to the number of qubits: IBM and some other research institutes have been working on an idea of connecting multiple quantum computers in a grid. This would potentially help alleviate the problem of "how to fit 1000s of qubits, with all the wiring, into a single fridge", as well as "how to fabricate high-quality single chip reliably". In theory, we could fabricate and wire-up medium sized-chips, setup full quantum computers and connect them with some sort of quantum memory and quantum communication channels. Fabrication is tough; the company I work at does it all, from fabrication of quantum chips to final on-premise installation, and fabrication is as difficult as one can imagine.