3 ms·

So the number of raw qubits are in the order of a million for large prime factorization or to make Shor's algorithm a reality. This is because the physical qubi

So the number of raw qubits are in the order of a million for large prime factorization or to make Shor's algorithm a reality. This is because the physical qubits are highly unstable and prone to errors. The error correction methodologies will result in a fault-tolerant logical qubit. Depending on the error correction algorithm, the ratio of logical: data/physical qubit is 1:1000 at the minimum. You need 4000 logical qubits at least for large prime factorization give or take 4 million raw qubits.

amelius 8y ago
How fast do you think the number of qubits will grow over the coming years? Will it be exponential, like Moore's law?
- misterprime 8y ago
  There was an AMA not long ago with someone in the quantum computer industry and iirc he stated that it isn't certain if we even can go that high. Guessing how fast that will happen is not reasonable at this point.
bscphil 8y ago
This is probably a dumb question, but could you spread out the error correction in time? I know it's hard to create very large entangled systems, so would it be possible/easier to do the calculation with 4000 real qubits 1000 times and use the repetition for error correction? (Checking for correct factorization is easy, after all.)
- simcop2387 8y ago
  That's been one strategy I've seen mentioned in regards to Shor's algorithm many times. Since there's the probability of an error, you still have to check it and rerun it a few times until you confirm the right answer. That's still many times faster than you'd get conventionally, so it's a reasonable trade off. But it doesn't address the possibility that you can't entangle enough qubits to begin with, or keep them stable long enough to actually perform the calculations, which is where the error correction stuff comes in. I don't know enough about the challenges there to comment on how many you'd need (though 1000:1 seems high to my naive intuition, i'd guess maybe 10-100 for magnitude myself).
  - sir_kin 8y ago
    For more info on that 1000:1 ratio, see [1]. [1] https://en.wikipedia.org/wiki/Quantum_threshold_theorem https://en.wikipedia.org/wiki/Quantum_threshold_theorem
- mirekrusin 8y ago
  Calculation on quantum state is already spread in time. Each time you calculate something you basically take snapshot of the state. Then you do it again. After many trials patterns emerge - that’s when you start reading your answer - which is always probabilistic.
wiz21c 8y ago
>>> qubits are highly unstable newbie question : are they naturally instable (so we won't fix that) or is it just because we don't master them well enough right now (and we'll fix them "soon") ?
- deepGem 8y ago
  It's the former. They can be made stable at super conducting temperatures but not completely. There will always be errors. From what I can understand you cant fully eliminate the errors. I donno may be some new superconducting temp might make them stable but that's a wild guess.

amelius 8y ago

How fast do you think the number of qubits will grow over the coming years? Will it be exponential, like Moore's law?

misterprime 8y ago
There was an AMA not long ago with someone in the quantum computer industry and iirc he stated that it isn't certain if we even can go that high. Guessing how fast that will happen is not reasonable at this point.

bscphil 8y ago

This is probably a dumb question, but could you spread out the error correction in time? I know it's hard to create very large entangled systems, so would it be possible/easier to do the calculation with 4000 real qubits 1000 times and use the repetition for error correction? (Checking for correct factorization is easy, after all.)

simcop2387 8y ago
That's been one strategy I've seen mentioned in regards to Shor's algorithm many times. Since there's the probability of an error, you still have to check it and rerun it a few times until you confirm the right answer. That's still many times faster than you'd get conventionally, so it's a reasonable trade off. But it doesn't address the possibility that you can't entangle enough qubits to begin with, or keep them stable long enough to actually perform the calculations, which is where the error correction stuff comes in. I don't know enough about the challenges there to comment on how many you'd need (though 1000:1 seems high to my naive intuition, i'd guess maybe 10-100 for magnitude myself).
- sir_kin 8y ago
  For more info on that 1000:1 ratio, see [1]. [1] https://en.wikipedia.org/wiki/Quantum_threshold_theorem https://en.wikipedia.org/wiki/Quantum_threshold_theorem
mirekrusin 8y ago
Calculation on quantum state is already spread in time. Each time you calculate something you basically take snapshot of the state. Then you do it again. After many trials patterns emerge - that’s when you start reading your answer - which is always probabilistic.

wiz21c 8y ago

>>> qubits are highly unstable newbie question : are they naturally instable (so we won't fix that) or is it just because we don't master them well enough right now (and we'll fix them "soon") ?

deepGem 8y ago
It's the former. They can be made stable at super conducting temperatures but not completely. There will always be errors. From what I can understand you cant fully eliminate the errors. I donno may be some new superconducting temp might make them stable but that's a wild guess.