Physicists take a key step in correcting quantum computer errors
science.org
science.org
It's actually from last year, and other groups have done better experiments since then (in particular, experiments doing multiple rounds of correction instead of just immediately smashing the system and analyzing the pieces). It's quite funny to see a big deal being made of this paper now rather than a year ago.
Perhaps reality is actually only approximated by the wave function but reality is something else under the surface which means quantum computers may need to be reconsidered.
I highly recommend reading [1] for an overview of the various skeptical viewpoints on quantum computing. Note that, while Aaronson argues most of the initial arguments are trivially wrong, he admits that whether or not error correction is fundamentally impossible is an open question.
We can keep solving the engineering challenges, but the universe might simply not allow us to get a return on investment with every additional qubit.
QC in contrast must exist or else QM is fundamentally wrong - not incomplete, but wrong.
We know its possible to have a fusion reactor, we would just have to dump enough mass together to build a sun. Hopefully we can make it more cost effective.
There isn't a natural phenomena that solves a problem by encoding it and (ab)using quantum physics.
2. Everything after the first sentence doesn't make sense. Any system that implements a restricted class of unitaries and features local measurement as described by Born's rule can efficiently solve problems in BQP. We have no reason this should apply to 10 qubits and not 1000.
The theory of quantum mechanics has been completely predictive in materials and has resulted in the most accurate predictions in nature (Anomalous magnetic dipole moment to a part in a trillion.) It doesn't matter if the theory is "Macroscopic" or whatever, it's predictive and within the constraints of its predictions you have known computational power up to problems in BQP. Whether BQP=P is an open question, but as is P=NP.
Known problems are things like wiring, materials science/sources of noise -- eventually including things like cosmic rays. It should work and we have no reason to think it shouldn't due to fundamental limitations of the natural world. It is, however, one of the hardest scientific things humans have ever tried to do so far. To say it'll definitely work is hubristic.
[1] https://plato.stanford.edu/entries/qm-collapse/#ContSponLoca...
[2] https://en.wikipedia.org/wiki/Ghirardi%E2%80%93Rimini%E2%80%...
When I talked about a "fundamental limit on how big you can make a quantum computer" I wasn't talking about it's physical size, I was talking about the number of mutually entangled qbits it contains, and the amount of time it is able to maintain those entanglements in a coherent state.
There's apparently noise in the system - how do we know that the reality is different to the model, and what we are putting down to noise is actually reality being different to the model? Kind like Einstein's correction of Newton.
That being said, if physics derisking failed, it seems really unlikely to me that it would be because quantum mechanics itself was wrong as opposed to there just being some unforseen problematic error mechanism that was consistent with quantum mechanics. Finding a flaw in quantum mechanics itself would be a scientific revolution, which would be awesome, but those are also pretty rare.
I also think it's a little telling that people keep thinking it's the philosophically unsatisfying parts of quantum mechanics that are going to break, when entering a new regime. It smells of confirmation bias.
Disclaimer: am on google quantum team.
Up to 12 qubits or so.
> Perhaps reality is actually only approximated by the wave function but reality is something else under the surface which means quantum computers may need to be reconsidered.
Possible, that reality is only approximated, and that approximation breaks down at more qubits. However, that would be the more exiting outcome, since then we have an experiment that gives us a window into a post quantum theory.
It is, in my opinion, not much more credible than perpetual motion or free energy, and less credible than cold fusion...
There are various applications. Some that you hear about most might be a little overblown (but still maybe not). For example, quantum simulation is an application within the physics field that already makes these systems worthwhile to pursue, without any mention of breaking encryption and the other things mentioned. Quantum logic, i.e. quantum computing on the smallest scale, has been employed to make cutting-edge atomic clocks (which are undeniably a worthwhile pursuit, with countless applications in the real world).
Putting "scaling up quantum computing, the pieces of which have already been demonstrated" in the same sentence as perpetual motion and free energy (known to be in violation of laws of physics) is completely unjustified.
My intuition is that large scale quantum computing is also in violation of laws of physics, but we don't have good models/theory about those yet.
What I am calling for is a reality check on this field.
Pretty much like string theory I am ready to bet it won't go anywhere.
That possibility alone is worth all of the investment in this field.
In contrast, String Theory is just an extension of QM, motivated by nothing except some cool looking math. It doesn't even make any definite predictions (supersimmetry is possible in string theory, but not required, at least not at any particular energy level).
It is already known that many of the most physically important quantum field theories are actually string theories if you rewrite them in different variables (this is called AdS/CFT duality), especially for understanding their large-coupling behavior string theory is the only tool available to analytically understand the theory. So string theory being completely wrong would be as surprising as quantum computing being impossible, for the same reason as you gave for QC. It would indicate something profoundly wrong about something we think we understand well. Its not impossible but the case is much, much more robust than the general internet understands.
And yes, to the extent that it's the same formulae as QM, finding counter-example would be fascinating. But (higher-dimensional) string theory could be wrong with no impact on QM/QFT.
In other words I’m not saying that string theory is (only) a generalization of known correct physics, but that many string theories are equal to (and therefore by definition as physically valid as) physically important quantum field theories. Then there are other string theories that are truly interesting and novel, too.
Additionally, this conjecture is actually experimentally verifiable—you can set up strongly coupled systems in the lab and study the string theory description, and compare the predictions.
Given that Quantum Computing has yet to deliver on its promise after decades of work and huge investment, I think it is safe to compare the field to other fringe science that once occupied some of the best minds on the planet (like Newton and his obsession with Alchemy).
To me, string theory feels like a fringe science; and irritating one at best.
There's another aspect too: the more generic comments are, the more predictable they are. Since they don't contain much actual information, there's nothing really new to say, which means people repeat the same things over and over. Often they get angry as they do it, since indignation usually fills the vacuum when curiosity is absent.
All of this is the opposite of what we're looking for on HN. What we want: specific, unpredictable, curiosity-gratifying conversation.
https://hn.algolia.com/?dateRange=all&page=0&prefix=true&sor...
https://hn.algolia.com/?dateRange=all&page=0&prefix=false&so...
Why do we think it is more valid than Alchemy?
More work is needed to turn quantum enhanced optimization into a practical technology. The design of next- generation annealers must facilitate the embedding of problems of practical relevance.
Like fusion, current progress is promising, but practical results lie in the future?
If quantum computing was not possible, that would mean that everything we thought we knew about physics was hopelessly wrong. Physics would have to be much stranger - we'd have to give up on either locality (i.e. causation being limited by the speed of light), reversibility (closely related to conservation of energy), or nondeterminism in order to make the math work out. There are several papers in the literature that derive quantum mechanics from these or related assumptions (often together with some extra technical detail, that differs between approaches):
https://arxiv.org/abs/quant-ph/0101012 https://arxiv.org/abs/1011.6451 https://arxiv.org/abs/0911.0695
Using rock-solid math and physics I think you can do time travel and speculate about parallel universes, but I don't think we should blindly believe the models.
We should never confuse the map and the territory.
30 years is nothing given how complex the engineering problem is of actually building a working QC. Fusion is much simpler and very well understood and yet it has been more than 50 years since research into fusion power plants has started, and the most optimistic estimates say we'll have the first ever research power plant 30 years from now, if everything goes well (EUfusion's DEMO plant).
Speculating about parallel universes is a different story - even if they exist, we can't travel to them, so there is no sense in claiming that we can somehow harness their power. It's a philosophical question, not a physical one. In contrast, the rules of quantum mechanics (when phrased in terms of density matrices, at least) only describe things we can actually measure and observe, and people actually do test every single aspect of the predictions quantum mechanics makes.
This is false. Time travel to the future is possible and proven[0]. Perhaps you are referring to traveling to the past.
[0] https://en.m.wikipedia.org/wiki/Experimental_testing_of_time...
Backwards time travel isn’t possible in general relativity, though, making very mild and physically plausible assumptions about the spacetime. Same in semiclassical quantum gravity.