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via:博客园 time:2020/8/29 20:01:12 readed:721

Xiaocha from Aofei Temple

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Today, Google's quantum computer appeared on the cover of science. They successfully simulated the isomerization of diazene with 12 qubits.

This is the second time that Google quantum computer has been on the cover of a top academic journal.

Last October, Google's quantum compute

What else can this quantum computer do? Google said it could mimic chemical molecules. In less than a year, they did.

Because molecules follow quantum mechanics, it is more reasonable to use quantum computing to simulate them. The properties of chemicals can be calculated with less computation and information.

Quantum computer simulation of chemical molecules is of great use. In addition to Google, other companies with quantum computing technology are also studying, including Microsoft.

Last month, Microsoft published an article using quantum computing to help chemists find catalysts to convert carbon dioxide to formaldehyde. The application prospect of the combination of quantum computation and chemistry is shown.

Quantum chemistry still needs quantum computers

Schrodinger equation is the basis of quantum chemistry and the basic law of chemical molecules. The specific chemical properties of matter can be obtained by solving the equation.

However, it is not easy to solve the Schrodinger equation. With the increase of the number of atoms in the molecule, the calculation of the solution equation increases exponentially.

Take the simple benzene molecule (C6H6) in chemistry as an example. It has only 12 atoms, but the calculation dimension reaches 1044, which is beyond the processing of any supercomputer.

In order to simplify the solution process, there were some approximate methods, such as those used by Google, long before the computer appeared

What's worse, in the process of chemical reaction, that is, the chemical bond dissociation, the electronic structure of molecular system will become more complex, and it is difficult to carry out relevant numerical calculation on any supercomputer.

In 2018, someone proposed a new quantum algorithm. The computational complexity is no longer exponential growth, but polynomial growth, which greatly reduces the difficulty of calculation.

If we have all the algorithms, we need a proper quantum computer.

Google quantum computer simulation of chemical reactions

Google's Sycamore quantum processor last year entangled 53 qubits, so use it to simulate several simple chemical molecules.

Google first calculates the binding energy of a hydrogen chain of six to ten hydrogen atoms. The effect of the original method (yellow in the figure below) is not so good. When combined with vqe and other algorithms, the results obtained by quantum computer are almost identical with the real values.

This is the static process of chemical molecules, and then Google used sycamore to simulate a simple chemical reaction: the isomerization of diazene.

The gap between the cis and trans transitions of diazene is 40.2 millihardt, and the quantum computer results are 41

Although the accuracy is much worse than the previous simulation of the hydrogen atom chain, Google says this is

Although the above results can be simulated without a quantum computer, the work is still a big step forward in quantum computing, said the corresponding author of this paper, Ryan babbash.

In the future, this algorithm can be expanded to simulate more complex reactions. More qubits are needed to simulate the reactions of larger molecules.

Babbash believes that one day we can even use quantum simulations to develop new chemicals.

Reference link:

https://science.sciencemag.org/content/369/6507/1084

https://arxiv.org/abs/2004.04174

https://www.microsoft.com/en-us/research/publication/quantum-computing-enhanced-computational-catalysis/

https://www.newscientist.com/article/2253089-google-performed-the-first-quantum-simulation-of-a-chemical-reaction

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