Circuit-Efficient Qubit Excitation-Based Variational Quantum Eigensolver

Area of Science:

• Quantum computing
• Computational chemistry
• Quantum algorithms

Background:

• The adaptive derivative-assembled pseudo-trotter (ADAPT) variational quantum eigensolver (VQE) is a powerful framework for determining molecular ground and excited states.
• Constructing accurate wave function representations requires implementing complex quantum operators, often leading to deep quantum circuits.

Purpose of the Study:

• To develop a CNOT-efficient circuit for implementing exponentialized two-body qubit-excitation-based (QEB) operators within the ADAPT-VQE framework.
• To reduce the depth of quantum circuits used in VQE simulations without compromising accuracy.

Main Methods:

• Proposed a novel circuit architecture using a 2-qubit-controlled rotation gate and CNOT gates for implementing exponentialized two-body QEB operators.
• Integrated the optimized circuits into the ADAPT-VQE algorithm.
• Performed numerical simulations to assess accuracy and efficiency.

Main Results:

• The proposed circuit requires only 9 CNOT gates per two-body QEB operator.
• Achieved an approximate 28% reduction in circuit depth compared to the original QEB ADAPT-VQE method.
• Maintained accuracy in simulating ground- and excited-state properties of small molecules.

Conclusions:

• The developed CNOT-efficient circuit offers a significant improvement for ADAPT-VQE.
• This approach enhances the feasibility of quantum simulations for electronic structures on near-term quantum devices.
• The method preserves crucial symmetries such as particle number and spin.