Exploring variational circuits

In this section, we will be diving into the concept of variational circuits, which form an integral part of today's quantum machine learning algorithms and research. We will be briefly looking into the three most common variational methods – variational quantum classifier (VQC), variational quantum eigensolver (VQE), and quantum approximation optimization algorithm (QAOA). Let's start with VQC in the next section.

Variational quantum classifier (VQC)

VQC, as the name suggests, is a classifier that is composed of quantum circuits with variational parameters or trainable parameters. This is the basis for quantum neural networks. Since you are already familiar with the concepts of artificial neural networks, it will be easy for you to appreciate the nature of the variational circuit used for classifiers.

There are many different types of variational circuits available that can be used for quantum classifiers, and many of the circuit...