101–110 of 149 posts
The high order bit is that the IBM claims do not cast much of a shadow over the claims of quantum supremacy and still show the same exponential difference.
Following the quantum supremacy controversy is very frustrating. It gets constantly framed as a decisive step that changes everything, which is wrong. But then there's also an opposite and equally wrong reaction that any challenges to the claim prove that quantum computing doesn't work at all. The reality is that quantum computing technology has been improving at the same steady pace for decades, and quantum supremac…
Yes, Google probably can achieve quantum supremacy by slapping a few more qubits. But a few more qubits were, in fact, not slapped yet. So quantum supremacy is very much not achieved, and Google should not claim so.
Earlier quoted context omitted.
Isn't quantum factoring proven to be exponentially faster than the best known classical one? The only question is we don't know if there is a better classical factoring algorithm. Wikipedia: > On a quantum computer, to factor an integer N, Shor's algorithm runs in polynomial time. This is almost exponentially faster than the most efficient known classical factoring algorithm, the general number field sieve, which wor…
Yes, for factoring integers the best known quantum algorithm is better than the best known classical algorithm. The catch is that we don't know if a better classical algorithm exists but just wasn't discovered yet. Compare this for example to sorting. We have proven that any sorting algorithm working with comparisons can at best be O(n*log(n)) fast, it's impossible for a faster classical algorithm to exist.
You can have a faster classical algorithm if it's distributed across n threads for a size n array. For each index i in an array arr, spawn a thread that counts the number of values in arr that are less than arr[i] (an O(n) linear scan), call this x, then do outputArray[x] = (arr[i], 1), where outputArray is initialised to all zeros. If outputArray[x] already exists, instead increment the second term (count) in the tuple. Once all threads are finished, then outputArray will contain the sorted values and the count of duplicate values (so this only works if !(x < y) && !(y < x) implies y == x). Each thread does O(n) work, so total work is O(n^2), but because the threads all run in parallel, the runtime is only O(n).
Also of note is Gil Kalai's updated take on the experiment [1]. The heart of the complaint is that the quantum computer's solution to this problem relies on a calibration process, which is done on a classical computer and requires resources orders of magnitudes higher than the quantum portion of the computation: > The Google experiment actually showed that a quantum computer running for 100 seconds PLUS a classic com…
Crucial question - is the calibration a one time effort where the same calibration can be used to calculate any number of results within the calibrated space? In other words, can you amortize the calibration cost across 1,000 runs and come out an order of magnitude ahead?
Earlier quoted context omitted.
Crucial question - is the calibration a one time effort where the same calibration can be used to calculate any number of results within the calibrated space? In other words, can you amortize the calibration cost across 1,000 runs and come out an order of magnitude ahead?
See the comments on Kalai's post from Peter Shor, where Kalai attempts to address this, and my reply to mantap on this thread where I try to give my poor understanding of the critique.
Especially when Peter Shore is disagreeing with the critique (and I agree with him).
Saying that a quantum computation does not qualify because it included (a short) classic computation does not seem a fundamentally fair criticism to me.
This seems to be commonplace in academic publishing, especially new-ish fields where benchmarks aren't well-established. There was a similar backlash against OpenAI's robot hand, where they used simulation for the physical robotic movements and used a well-known algorithm for the actual Rubik's Cube solving. I still think it's an impressive step forward for the field.
Following the quantum supremacy controversy is very frustrating. It gets constantly framed as a decisive step that changes everything, which is wrong. But then there's also an opposite and equally wrong reaction that any challenges to the claim prove that quantum computing doesn't work at all. The reality is that quantum computing technology has been improving at the same steady pace for decades, and quantum supremac…
Quantum supremacy is a big deal. It is a goddamn experimental evidence against Extended Church-Turing Thesis. If you never believed ECT (for example, all physicists seem to think ECT is obviously false) it may not matter to you, but it still is a serious claim. Yes, Google probably can achieve quantum supremacy by slapping a few more qubits. But a few more qubits were, in fact, not slapped yet. So quantum supremacy i…
That's why arguing over whether it's really quantum supremacy is just not useful. People can always move the goalposts, so we might as well ban that word from discussion. The underlying fact, which nobody is debating, is that quantum computers are regularly doing tasks that are harder and harder for classical computers to.
And yes, the ECT is obviously false -- or at the very least, not obviously true. I'm surprised at how many CS people think it is some unassailable principle. Most CS courses devote precisely zero time to non-classical models of computation. If you've never studied a model of computation that could challenge ECT, then how can you be so sure of it? This is like being absolutely certain that I am the tallest person in the world, and refusing to ever leave my house to check.
Earlier quoted context omitted.
Those are all about problems started in terms of querying some blackbox oracle. Whether the speedup holds up with a concrete instantiation of the blackbox is unknown.
Could you elaborate? You can search for the solution to any computational problem for which there is a binary function f(n) mapping candidates n to {0,1}, depending on whether it's a solution. Here, f is the "oracle", but it's only playing the role of representing the problem you're trying to solve, and I believe an f exists for all problems in NP. If your set of solutions has N candidates, this requires only O(sqrt(…
Is IBM still relevant?