"Why do mathematicians think" quantum computer is not realized "?

byAlex Sukontsev

It is considered to realize ultra-fast calculation using the principle of quantum mechanicsQuantum computerHowever, there is still a long way to realize itThere is a challengeIt has been with. Mathematician'sGil KaraiMr"Quantum computer is not realizedQuanta Magazine takes up the opinion of Mr. Karai.

Gil Kalai's Argument Against Quantum Computers | Quanta Magazine
https://www.quantamagazine.org/gil-kalais-argument-against-quantum-computers-20180207/

It was held in Yale University in February 2002Michael DeborahMr. Karai participated in a lecture on Mr. Quantum computer. Mr. Deborah was a leader in quantum computers, but because the title of the lecture was "Quantum computer: a miracle or a mirage?", Mr. Karai said, "For the process of quantum computers and the results obtained I thought that it would be a skeptical discussion. " However, in reality there are few skeptical opinions on quantum computers, Mr. Karai who seemed disappointed he started research with a skeptical stance against quantum computer.

Currently Mr. Karai is a mathematician who works for the Hebrew University in Israel and takes the position that "quantum computer is only a mirage". Researchers skeptical of quantum computers said, "There is a quantum computer inside,Qubit"It will not work as expected by the developers." Some researchers say that quantum computers themselves can not be created, but some researchers say that "Quantum computers can be made, but it is difficult to exceed the performance of currently used computers".

Mr. Karai examined the quantum computer from the viewpoint of mathematicians and computer scientists and reached the conclusion that it is necessary to solve 'noise' to realize the quantum computer. "Noise" is a word that refers to an error that occurs in the process in which the quantum computer operates. In a quantum computer, it is essential to keep quantum bits "quantum superimposed" without interference from the outside world, but since qubits tend to be damaged by interaction with the outside world, interference from the outside world It can not be avoided.

bySteve Jurvetson

Mr. Karai admits himself as a minority, as large companies like IBM, Intel and Microsoft are making large contributions to quantum computers and being promoted as a national project in China and elsewhere. Mr. Karai said that he did not have a skeptical stance with quantum computers from the beginning. After listening to the lecture in 2002, it seems that since 2005 it began full-scale efforts to solve the problem "Quantum computer is just a mirage?"

"I see it as a concept that 'noise' can not be avoided in the realization of quantum computers," Karai said. When noise is generated at a certain point when the quantum computer executes the process, it is said that noise spreads throughout the quantum computer, causing quantum computers to malfunction.

In order to solve the noise generated in the quantum computer and to operate the quantum computer,Quantum error correction"Is essential. In quantum error correction, in order to keep a certain quantum bit in an ideal state, another multiple quantum bit is attached to correct an error due to noise. However, in order to implement quantum error correction, in order to realize one ideal quantum, "keep the noise below a certain level", hundreds of high quality qubits will be required as it is.

byRon Mader

Mr. Karai said, "Quantum bits of quantum computers are sensitive to each other, so the more quantum bits, the more likely one noise will affect other qubits." Then,Fourier analysisWe analyzed the effect of quantum bit noise on the quantum computer by decomposing complex waveforms in the calculation of quantum computers into simple elements.

As a result, Mr. Karai has found that the waveform after the Fourier transform by the noise is canceled at the high frequency part, and when noise occurs, only the low frequency part remains. "This is the same as not being able to hear the violin or viola, although it can be heard in Beethoven," Karai says.

And it seems that Mr. Karai has concluded that it is very difficult to add quantum error correction for canceling noise to the quantum computer. "Although we can not make quantum computers even in the presence of noise, it is lower performance than existing computers," he said.

byUCL Mathematical & Physical Sciences

Mr. Karai said, "It is impossible to extend my argument from" a simple mathematical model to an objection on a physical device "" Reducing noise is an engineering problem and it can be solved by putting in resources " Some people criticize, but if we try to make a quantum computer with a low noise, the necessary quantum error correction will increase exponentially and it will not be able to catch up forever. "

And, "I am confident in my theory, but somewhere I think" I can only make a mistake. "I just wait for the result to be proved." It was.