# Google quantum computing on the cover of science quantum simulation of chemical reactions

Qubit report official account No. QbitAI

Today, Googles 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.

In October last year, Googles quantum computer made its appearance on the cover of nature because of its quantum superiority. It took only 200 seconds to solve the sampling problem of quantum circuits, which takes 10000 years to solve for Supercomputing.

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 simulate them by quantum computation. With less computation and information, the properties of chemical substances can be calculated.

Quantum computer simulation of chemical molecules is of great use. In addition to Google, other companies with quantum computing technology are also working on it. Microsoft is one of them.

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 computational complexity of solving the 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 approximation methods long before the advent of computers, such as Hartley Fogg equation used by Google. But even after simplification, the amount of computation is huge.

Whats 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

Googles sycamore quantum processor implemented 53 qubits entanglement last year, so lets use it to simulate a few 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.

The energy gap of diazene transition between CIS and Trans is 40.2 MHT, and the result of quantum computer is 41 u00b1 6 MHT.

Although the accuracy is much lower than the previous simulation of hydrogen chains, Google said it was the first time that a quantum computer was used to predict chemical reaction mechanisms.

Although the above results can be simulated without a quantum computer, the work is 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://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/

Source: Quantile editor: Wang Fengzhi_ NT2541