  For a large number of tasks, quantum computing demonstrates the potential for
exponential acceleration over classical computing. In the NISQ era,
variable-component subcircuits enable applications of quantum computing. To
reduce the inherent noise and qubit size limitations of quantum computers,
existing research has improved the accuracy and efficiency of Variational
Quantum Algorithm (VQA). In this paper, we explore the various ansatz
improvement methods for VQAs at the gate level and pulse level, and classify,
evaluate and summarize them.
