New Quantum Approach Enhances Simulation of Chemical Reaction Dynamics

Researchers from Origin Quantum Computing Company Limited, the Institute of Artificial Intelligence Hefei Comprehensive National Science Center, and the University of Science and Technology of China have developed a new quantum approach to simulating chemical reaction dynamics. The method, known as eCSVQE, extends the Correlated Sampling (CS) method based on the Variational Quantum Eigensolver (VQE) algorithm.

The eCSVQE approach simulates dynamics processes for chemical reactions, achieving high-precision reaction dynamics trajectories. It is less demanding on quantum computing resources, making it feasible for the dynamics simulation of chemical reactions on current quantum devices.

What is the New Quantum Approach to Simulating Chemical Reaction Dynamics?

A team of researchers from Origin Quantum Computing Company Limited, the Institute of Artificial Intelligence Hefei Comprehensive National Science Center, and the CAS Key Laboratory of Quantum Information School of Physics at the University of Science and Technology of China have developed a new quantum approach for simulating chemical reaction dynamics. This approach extends the Correlated Sampling (CS) method based on the Variational Quantum Eigensolver (VQE) algorithm, which has been labeled as eCSVQE.

The CS method was initially proposed by Fedorov et al. and demonstrated the vibrational dynamics of H2 molecules. The researchers have extended this method to three-dimensional cases for the calculation of first-order energy gradients and further generalized it to calculate the second-order gradients of energies. By calculating atomic forces and vibrational frequencies for H2, LiH, HH2, and ClCH3Cl systems, the team has achieved the CCSD level of accuracy.

How Does the eCSVQE Approach Work?

The eCSVQE approach simulates dynamics processes for two typical chemical reactions: hydrogen exchange and chlorine substitution. The team obtained high-precision reaction dynamics trajectories consistent with classical methods. The eCSVQE approach is less demanding in quantum computing resources as measurement expectations and ground state wave functions can be reused. This makes it feasible to simulate chemical reactions in dynamics on the current noisy intermediate-scale quantum-era quantum devices.

What is the Significance of Simulating Chemical Reaction Dynamics?

Chemical reaction dynamics involving chemical transformations are central phenomena in physical chemistry. These dynamic processes usually occur on the femtosecond scale and include the breakage of old bonds and the formation of new bonds resulting from electron redistribution. Therefore, it is necessary to use quantum mechanics to describe and characterize this process.

Chemical reaction dynamics have been studied using full quantum mechanical methods for about forty years and have led to the development of some techniques, such as wave packet-based and statistical methods. However, for large systems, describing the reaction process still poses significant challenges. Therefore, there is always a trade-off between accuracy and speed in many classical methods in which accurate reaction dynamics simulations are limited to small molecular systems due to the exponential increase in computational resource costs.

How Does Quantum Computing Aid in Simulating Chemical Reaction Dynamics?

Quantum computing, a new computing paradigm utilizing the superposition and entanglement of qubits, has a powerful processing speed and is expected to bring new solutions to chemical problems. The quantum algorithms widely used in the computational chemistry field include the Quantum Phase Estimation (QPE) algorithm and the Variational Quantum Eigensolver (VQE) algorithm.

The QPE algorithm is a quantum algorithm applied to calculate the ground-state energies of chemical systems. However, the algorithm needs many readout qubits to obtain an accurate eigenvalue. To reduce the number of qubits, Aspuru-Guzik et al. developed the recursive QPE to reduce the readout qubits to four. Furthermore, Dobšíček et al. proposed the iterative QPE, which needs only one readout qubit.

What are the Advantages of the VQE Algorithm?

The VQE algorithm has been widely studied and experimentally demonstrated on various quantum hardware platforms. In the VQE algorithm, a parameterized quantum circuit prepares a trial wave function and the expectation value of the electronic Hamiltonian is measured on quantum computers, while the optimization process for those parameters is performed on classical computers by minimizing the expectation value.

The VQE algorithm is based on the variational principle, thus the final set of parameters gives the upper bound for the ground-state energy of a given Hamiltonian. Therefore, the VQE algorithm combines the advantages of quantum computers and classical computers and is suitable for the current noisy intermediate-scale quantum (NISQ) hardware.