7.3 Using VQE with Qiskit
In this section, we will show how we can use Qiskit to run VQE on both simulators and actual quantum hardware. To do that, we will use a problem taken from quantum chemistry: determining the energy of the or dihydrogen molecule. Our first subsection is devoted to defining this problem.
7.3.1 Defining a molecular problem in Qiskit
To illustrate how we can use VQE with Qiskit, we will consider a simple quantum chemistry problem. We will imagine that we have two atoms of hydrogen forming an molecule and that we want to compute its ground state and its energy. For that, we need to obtain the Hamiltonian of the system, which is a little bit different from the kind of Hamiltonian that we are used to. The Hamiltonians that we have considered so far are called qubit Hamiltonians, while the one that we need to describe the energy of the molecule is called a fermionic Hamiltonian — the name comes from the fact that it involves fermions, that is, particles...
