jgeada
7 days ago
This is interesting, but what isn't mentioned is how long these devices can hold coherence (see https://en.wikipedia.org/wiki/Charge_qubit and https://en.wikipedia.org/wiki/Quantum_decoherence)
All existing QC approaches have two fundamental limitations: error rate and coherence time. You can decrease error rate through error correction, but that comes at the cost of adding gates and/or storage to replicate the QC state, but that causes a decrease in coherence time. I have not seen even a theoretical framework allowing both to be increased simultaneously.
Strilanc
7 days ago
> I have not seen even a theoretical framework allowing both to be increased simultaneously.
The threshold theorem [1], showing this can be done in principle, was proven more than a decade ago.
But you don't have to believe the theory anymore, there's experiments now! Last month the google quantum computing team published an experiment [2] showing memory error rates (including decoherence) getting twice as good as a surface code was grown from distance 3 to distance 5, and twice as good again going from distance 5 to distance 7. The logical qubit's coherence time was longer than the coherence times of the physical qubits it was built out of.
amirhirsch
7 days ago
I will bet $2048 that a quantum computer will not factor RSA2048 by 2048.
kurthr
7 days ago
I would not bet against you, but I suspect any advances will be made very quickly and that could happen any time in the next 25 years.
Even at 0.001% risk is far too much to take. I'd certainly make the $0.02 bet for those odds.
almostgotcaught
7 days ago
> I would not bet against you
So you don't think it'll happen by 2048
> but I suspect any advances will be made very quickly and that could happen any time in the next 25 years.
Um 2024 + 25 = 2049
kurthr
7 days ago
Yeah, I don't think there's a better than 50% chance of it happening before 2048, but I think there's a better than 0.001% chance that it does.
Yes, as a ring, the set of integers is closed under addition and 2049 is past the deadline so... it could happen before or after 2048?
amirhirsch
7 days ago
https://scottaaronson.blog/?p=8310 suggests perhaps the next decade for useful quantum computer. this suggests the scale for RSA2048: https://arxiv.org/pdf/1905.09749
The thing about this bet is you don't have to pay until 2048 whereas I have to pay as soon as it happens and accounting for savings rates the bet will cost about a dime a day.
kurthr
6 days ago
In my experience were really bad at figuring out when something more than about 5 years out is going to happen so 10-20 years is much worse than a coin flip. That's partially because we don't know what second and third order problems could come up, but also because interest/investment could change rapidly. For example, if some other probabilistic method of factoring primes (or even NP complete problems!) were discovered that would massively reduce funding for QC.
And yeah, there's a time value of money, inflation, repayment risk, and a zillion things that vary the value of a long term bet's payout, but at ~3-6%/yr they don't affect it by more than a few factors of 2. The risk of having all the world's stored encrypted data decrypted after the fact makes even a miniscule risk that QCs can break RSA or other encryption too big to accept. Those scale by many factors of 10.