Summary

In this chapter, we focused on implementing the Quantum Approximate Optimization Algorithm (QAOA), a hybrid algorithm. We started by using the phase adder circuit from Chapter 7, Using Gate Quantum Computers – Basic Quantum Algorithms, which has been modified for addition and subtraction. We used this to create a circuit that can sample all the possible solutions of an objective function. We found that this method provides equal probabilities of the different solutions and required a substantially large number of qubits and gate depth. To find the minimum value more efficiently, for optimization applications, it is necessary to be able to efficiently sample the lowest cost. We went over the concepts of how QAOA works and how its parameters impact the performance of the algorithm. We discussed that, in practice, the algorithm uses a classical optimization application to find the optimal parameters, and that this process is repeated in a few cycles to find the optimal...