Gil Kalai is not the only researcher who defends the impossibility of achieving quantum supremacy , but he is one of those who do so with more vehemence. This renowned Israeli mathematician who teaches at Yale ensures that we will never achieve this achievement because as the number of states of a quantum system increases, and therefore its complexity, it is more likely to behave like a classical one , which It would cause you to lose any advantage over a conventional machine.
Interestingly, the news that has seen the light in recent months seems to reinforce the opposite current, which states that quantum supremacy is near. Only a few days ago, IBM announced that it has already prepared a new quantum computer for commercial purposes with a capacity of 53 qubits , a great achievement if we look at that it is a machine for commercial applications. It is not a prototype. And only a few days later, the Financial Times newspaper revealed that Google had published an article on the NASA website claiming that it had reached quantum supremacy . Two forceful news that put quantum computing back to the center of the debate .
Quantum Supremacy: what it is and what it implies
It sounds very bombastic, but understanding what quantum supremacy is is simple. And it is only the milestone that we will reach when a quantum computer is faster in practice than a classic computer when both face the resolution of the same problem. Researchers who doubt that this is possible, including Gil Kalai, argue that quantum noise will not allow us to design efficient algorithms protected by robust error correction. And without a sufficiently reliable error correction, quantum computers lose their raison d’être because they become very expensive machines that contribute nothing to classic computers.
Quantum supremacy will come when a quantum computer is faster in practice than a classic computer when both face the resolution of the same problem
The most optimistic quantum computing researchers do trust that this barrier will be broken , although there is a solid consensus in accepting that achieving quantum supremacy is a challenge . Hence the Google ad is generating so much expectation. In any case, why is it so important to materialize this milestone? Simply because quantum supremacy will mark a deep turning point in the world of computing because it will allow us to solve problems that the supercomputers we currently have cannot face. For them to throw a solution would require an unassuming time.
The applications of quantum computing are very wide. In fact, thanks to it we can develop encryption procedures much more robust than the current ones; more advanced artificial intelligence algorithms; new synthetic materials that perhaps we cannot even imagine now, and we will also have closer to complex drugs that could help us fight more effectively some of the diseases we are currently facing, among other applications. Quantum supremacy will possibly be a very important step forward on this path, but not all problems are likely to be solved by resorting to quantum computing . Conventional computers will continue to be more efficient in some tasks.
This is what Google seems to have achieved, but casts doubt
The most striking, and at the same time suspicious, of this news is that the Google team of researchers led by John Martinis published his report a few days ago on the NASA website, and shortly after the article was removed. Apparently Google has a collaboration agreement with the US space organization that allows this company to use NASA’s supercomputers as a standard with which to calibrate the capacity of its quantum computers. In fact, the Martinis team article argues that “this experiment describes the first calculation that can only be carried out using a quantum processor .” This is the exact statement in which they claim to have achieved quantum supremacy.
However, there are several important notes that we cannot ignore. The first one is that, as I told you in the previous paragraph, the article that Google researchers published on the NASA website has been removed from the repository . We do not know why they made this decision, but it seems reasonable to think that it could be because they have doubts about the conditions in which the experiment has been carried out. Fortunately on the Internet everything leaves its mark, so if you want you can read the original article at this address .
The other reason why this “milestone” casts doubt has to do with the nature of the experiment that has been carried out by Google. Apparently the researchers have designed an algorithm that aims to generate random numbers through a very complex mathematical procedure, and that would force the Summit supercomputer of the Oak Ridge National Laboratory (United States), which is currently thanks to its 200 petaflops the most powerful of the world, to invest in this task no less than 10,000 years. But, according to Google researchers, its 54 qubits Sycamore quantum processor has solved this task in just three minutes and twenty seconds .
The tweet you have above this paragraph is the beginning of a very interesting thread in which a theoretical American physicist and cryptographer questions, after having read the article published by Google researchers, the way they have carried out the experiment. And therefore also its validity. One of his criticisms derives from the possibility that Google researchers have been able to simultaneously read the output of several qubits once their internal state has collapsed.
It is essential to have an efficient error correction system for the calculations to be valid
But his strongest criticism is closely linked to the argument of the mathematician Gil Kalai of which I spoke to you in the first lines of the article, and which raises the extreme difficulty of designing a robust error correction due to the presence of quantum noise , which is a disturbance that can ruin all the calculations. In fact, it is essential to have an efficient error correction system. Otherwise, the result may not be valid.
This is a very interesting topic, and also very complex, so the information we have is not enough to know with certainty whether Google has really achieved quantum supremacy. We hope that this company will soon publish more information that allows us to assess whether it has achieved it . We will be attentive to keep you promptly informed.