# VQEs

**What are Variational Quantum Egiensolvers?**

Variational quantum eigensolver (VQE) is a quantum algorithm that can be used to find the ground state energy of a Hamiltonian, as well as excited states of the Hamiltonian. The VQE algorithm is based on the variational principle, which seeks to find an ansatz (an approximation) to the ground state that has lower energy than the ground state itself. It has been shown that the VQE allows for universal quantum computing, making it a versatile tool for tackling a wide range of tasks. The VQE algorithm is versatile and can be applied to a wide range of tasks, making it a promising candidate for use in many applications of quantum computers. One particularly useful application of the VQE algorithm is in finding the ground state energy of a Hamiltonian. In this application, the algorithm is used to find an approximation to the ground state energy that is lower than the ground state energy itself. This is accomplished by minimizing a cost function that is based on the expectation value of the Hamiltonian. The VQE algorithm can also be used to find excited states of a Hamiltonian. In this application, the algorithm is used to find an approximation to an excited state of the Hamiltonian that is lower than the excited state energy itself.

This is accomplished by minimizing a cost function that is based on the expectation value of the Hamiltonian plus an additional term that…