First-quantized adiabatic time evolution for the ground state of a many-electron system and the optimal nuclear configuration

TL;DR

This paper introduces a first-quantized adiabatic time evolution method for efficiently finding the ground state of many-electron systems on quantum circuits without ancillary qubits, enabling optimal nuclear configuration searches.

Contribution

It presents a novel first-quantized ATE approach that simplifies implementation and allows for systems with any number of electrons, including a method for preparing initial states.

Findings

Successfully obtained electronic ground states in simulations.

Demonstrated optimal nuclear structure search capability.

Method avoids ancillary qubits and controlled operations.

Abstract

We propose a novel adiabatic time evolution (ATE) method for obtaining the ground state of a quantum many-electron system on a quantum circuit based on first quantization. As a striking feature of the ATE method, it consists of only unitary operations representing real-time evolution, which means that it does not require any ancillary qubits, nor controlled real-time evolution operators. Especially, we explored the first-quantized formalism of ATE method in this study, since the implementation of first-quantized real-time evolution on quantum circuits is known to be efficient. However, when realizing the ATE quantum circuit in first-quantization formalism, obstacles are how to set the adiabatic Hamiltonian and how to prepare the corresponding initial ground state. We provide a way to prepare an antisymmetrized and non-degenerate initial ground state that is suitable as an input to an ATE circuit, which allows our ATE method to be applied to systems with any number of electrons. In addition, by considering a first-quantized Hamiltonian for quantum-mechanical electron system and classical nuclear system, we design a quantum circuit for optimal structure search based on ATE. Numerical simulations are demonstrated for simple systems, and it is confirmed that the ground state of the electronic system and optimal structure can be obtained by our method.