Adding more qubits to the Grover search

So far, we have done reasonably well in our Grover coding. We built our two and three qubit circuits using unique Qiskit® gates for the number of qubits that our circuits contained: CX and CCX. For a four qubit and more Grover, we will use a multi-control NOT gate, MCX, to dynamically create the right number of control inputs.

Getting ready

We will use the same sample functions as in the Building the Grover's search algorithm recipe.

For two and three qubit Grovers, we could use the prefabricated CX and CCX gates to create our oracle and amplifier circuits. As we are using the same model to build a four and more qubit Grover, instead of using CCCX, CCCCX gates, and more, we use the MCX gate in our circuit, to let Qiskit® build the gate logic behind the scenes.

Note

To understand what we are doing here, take a look back at Chapter 6, Understanding the Qiskit® Gate Library, specifically at the CX and CCX gates...