Chapter 7
Parameterised Quantum Circuits and Data Encoding
Having built the quantum hardware, how can we use it to the maximum effect given its scale, connectivity, and fidelity rate? This question can be best answered if we split it into two parts. First, what problems are in principle solvable on NISQ computers? Second, how do we encode classical data into quantum states?
The rest of this book focuses on the first part: problems and models that can be formulated in a way that doesn’t require a massive number of qubits and that are, at least to some extent, noise tolerant. The first step in this direction is the concept of the Parameterised Quantum Circuit (PQC) as a generic quantum machine learning model.
The second part – data encoding – is equally important and relies on several practical methods described in this chapter. This is an active area of research where we can expect most of the progress to come from the quantum software side.
