[HN Gopher] Quantum Error Correction Goes FOOM
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Quantum Error Correction Goes FOOM
Author : EvgeniyZh
Score : 59 points
Date : 2025-12-25 09:18 UTC (13 hours ago)
(HTM) web link (algassert.com)
(TXT) w3m dump (algassert.com)
| sparedwhistle wrote:
| What the hell is FOOM?
| MattPalmer1086 wrote:
| Usually refers to a sudden increase in AI intelligence to super
| intelligence, i.e. the singularity. Basically an exponential
| increase in capability.
| austinjp wrote:
| It may also be a reference to the (comparatively ancient)
| "Pentium go F00F" bug.
|
| https://en.wikipedia.org/wiki/Pentium_F00F_bug
| AlexCoventry wrote:
| Explosive ignition of a fire.
| cubefox wrote:
| It was Yudkowsky's colloquial term for hard takeoff:
|
| https://www.lesswrong.com/posts/tjH8XPxAnr6JRbh7k/hard-takeo...
| layer8 wrote:
| https://en.wiktionary.org/wiki/foom#English
| amluto wrote:
| I'm amused by the burying of the non-lede until half way through
| the paper. I, too, can maintain a 59-bit repetition code for over
| two hours on my quantum laptop (it's just a normal laptop, but it
| definitely obeys the laws of quantum mechanics):
|
| Initialize the coded bit, using a 59-qubit repetition code that
| corrects bit flips but not phase errors, in IPython:
| In [1]: A = 59 * (False,)
|
| Write a decoder: In [2]: def decode(physbits):
| ...: return sum(physbits) > len(physbits)/2.0
|
| Wait two hours [0]. I'll be lazy and only decode at the end of
| the two hours, but if I wanted error correction to get the full
| advantage, I would periodically run the error correction
| algorithm and fix detected errors. Now decode it:
| In [3]: decode(A) Out[3]: False
|
| Holy cow, it worked!
|
| I'm being rather tongue-in-cheek here, of course. But it's
| genuinely impressive that my laptop can stick 59 bits into DRAM
| cells containing a handful of electrons each, and _all_ of them
| are just fine after several hours. And it 's really really
| impressive that this research group got their superconducting
| qubits to store _classical_ states well enough that their rather
| fancy error correcting device could keep up and preserve the
| logical state for two hours. [1]
|
| But this isn't _quantum_ error correction going FOOM, per se. It
| 's classical. A bit-flip-corrected but not phase-flip-corrected
| qubit is precisely a classical bit, no more, no less.
|
| The authors did also demonstrate that they could do the same
| trick correcting phase flips and not bit flips, but that's a tiny
| bit like turning the experiment on its side and getting the same
| result. Combining both demonstrations is impressive, though --
| regardless of whether you look at the DRAM cells in my laptop as
| though the level is the Z basis or the X basis, they only work in
| one single basis. You cannot swap the role of level and phase in
| DRAM and get it to still work. But the researchers did pull that
| off on their two-hour-half-life device, and I find that quite
| impressive, and the fact that it worked strongly suggests that
| their device is genuinely 59 _qubits_ , whereas no one could
| credibly argue that my laptop contains giga-qubits of DRAM.
| Fundamentally, you can do classical repetition using a repetition
| code, but you cannot do quantum computation with it. You need
| fancier, and more sensitive-to-errors, codes for this, and that's
| what the second half of the article is about.
|
| [0] I didn't actually wait two hours. But I could have waited a
| week and gotten the same result.
|
| [1] The researchers' qubits are nowhere near as good as my DRAM.
| They had to run their error correction a billion times or so
| during the course of their two hours. (My DRAM refreshes maybe
| ten thousand times over the course of two hours, and one can look
| at DRAM refreshes as correcting something a bit like a repetition
| code.)
| Strilanc wrote:
| Author here: yes that's all correct.
|
| This is perhaps not clear enough, but the title refers to a
| _pattern_. For classical bits on a quantum computer this
| pattern is already playing out (as shown in the cited
| experiments), and for quantum bits I think it 's about to play
| out.
|
| Classical storage of classical bits is still far more reliable,
| of course. Hell, a rock chucked into one bucket or another is
| still more reliable. We'll never beat the classical computer at
| storing classical bits... but the rock in a bucket has some
| harsh competition coming.
|
| I should maybe also mention that arbitrarily good qubits are a
| step on the road, not the end. I've seen a few twitter takes
| making that incorrect extrapolation. We'll still need hundreds
| of these logical qubits. It's conceivable that quantity also
| jumps suddenly... but that'd require even more complex block
| codes to start working (not just surface codes). I'm way less
| sure if that will happen in the next five years.
| amluto wrote:
| I don't really expect fancier codes to cause a huge jump in
| the number of logical qubits. At the end of the day, there's
| some code rate (logical bits / physical bits) that makes a
| quantum computer work. The "FOOM" is the transition from that
| code rate changing from zero (lifetime of a logical bit is
| short) to something that is distinctly different from zero
| (the state lasts long enough to be useful when some credible
| code). Say the code rate is 0.001 when this happens. (I
| haven't been in the field for a little while, but I'd expect
| higher because those huuuuge codes have huuuuge syndromes,
| which isn't so fun. But if true topological QC ever works, it
| will be a different story.) The code rate is unlikely to ever
| be higher than 1/7 or so, and it will definitely not exceed
| 1. So there's at most a factor of 1000, and probably less, to
| be gained by improving the code rate. This isn't an
| exponential or super-exponential FOOM.
|
| A factor of 1000 may well be the difference between
| destroying Shor's-algorithm-prone cryptography and destroying
| it later, though.
| vlovich123 wrote:
| But you still believe that quantum computers have a
| likelihood of being possible to build AND that they can
| accomplish a task faster than classical? I feel like it's
| going to get exponentially harder and expensive to get very
| small incremental gains and that actually beating a classical
| computer isn't necessarily feasible (because of all the error
| correction involved and difficulty in manufacturing a
| computer with large number of qbits). Happy to be proven
| wrong of course.
| Havoc wrote:
| Does quantum speed even matter?
|
| I would have thought a wide enough array of qubits could
| functionally do "anything" in one shot
| tsimionescu wrote:
| They most certainly can't, not even close to it. They can do a
| very limited subset of problems, and not at all in one shot -
| just far far far less shots than a classical computer. But even
| if you reduce and O(e^n) problem to an O(n) or O(n2) problem,
| that's not instantaneous, and the speed with which you perform
| these n or n2 operations still matters.
| Strilanc wrote:
| Yes, speed matters. No, quantum computers can't do everything
| instantly even with unbounded qubits.
|
| A well studied example is that it's impossible to parallelize
| the steps in Grover's algorithm. To find a preimage amongst N
| possibilities, with only black box access, you _need_
| O(sqrt(N)) sequential steps on the quantum computer [1].
|
| Another well known case is that there's no known way to execute
| a fault tolerant quantum circuit faster than its reaction depth
| (other than finding a rewrite that reduces the depth, such as
| replacing a ripple carry adder with a carry lookahead adder)
| [2]. There's no known way to make the reaction depth small in
| general.
|
| Another example is GCD (greatest common divisor). It's
| conjectured to be an inherently sequential problem (no polylog
| depth classical circuit) and there's no known quantum circuit
| for GCD with lower depth than the classical circuits.
|
| [1]: https://arxiv.org/abs/quant-ph/9711070
|
| [2]: https://arxiv.org/abs/1210.4626
| tbrownaw wrote:
| There is a complexity class called BQP, which is more or less
| the things that quantum computers are good at. This includes P
| which is more or less the things they normal computers are good
| at. Things that quantum computers are _better_ at would more or
| less be one minus the other. One interesting point is that BQP
| probably doesn 't include all of the rather famous NP class.
| moffkalast wrote:
| Everything is possible when a quantum scientist needs to apply
| for another grant. Less so after the project is already signed.
| oh_my_goodness wrote:
| Look at the last plot.
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