Advances in analog simulations of quantum chemistry

[ Instrument Network Instrument R & D ] Computer simulation based on quantum chemistry is widely used in the research of modern chemical reaction processes. But with the increase in the number of atoms in the molecule, the number of degrees of freedom in the system has increased dramatically, which has exceeded the computing power of classic supercomputers. In order to study the reaction process of complex molecules, quantum simulation methods can be used, that is, chemical reactions are simulated by precisely controlling and adjusting cold atom systems.

In a recent research work (Nature 574, 215 (2019)) participated by Shi Tao, an associate researcher at the Institute of Theoretical Physics, Chinese Academy of Sciences, an analog simulation of quantum chemistry was achieved by designing cold atoms in the optical lattice. During the chemical reaction, the nature of a molecule is determined by its outer electronic structure, and there is a Coulomb interaction between the electrons. Therefore, a crucial issue for analog simulations in quantum chemistry is how to achieve Coulomb interactions between neutral atoms. We know that in an electronic system, two electrons generate a Coulomb force by passing a virtual photon. Based on a similar mechanism, a scheme can be designed to achieve the Coulomb interaction between neutral Fermi atoms. In this scheme, a Fermi atom moving in the background of a Bose atom is used to simulate the electrons in the molecule, and the background Bose atom is caused to transition from the ground state to the excited state by an external laser field. These excited medium Bose atoms can freely propagate in the optical lattice like photons, thereby inducing interactions between Fermi atoms. Through effective design of the frequency and intensity of the laser field, the scattering length of atomic collisions, and the atomic dispersion relationship, the Coulomb interaction between Fermi atoms can be achieved.

This solution can not only be used to simulate small molecules, such as hydrogen molecules and helium molecules, but also to quantum simulation of complex intermolecular chemical reactions formed by multiple atoms. By comparing the calculation results of classical supercomputers in small molecule systems, the validity of this quantum chemical simulation scheme can be verified. In future work, through quantum simulation of chemical reactions of complex molecules, we can explore various chemical reaction processes that are difficult to study in modern classic supercomputers.