
Learn Quantum Computing with Python and IBM Quantum
By :

For most of the examples in this book, you will notice that we reuse a simple two-qubit quantum circuit to run many of our experiments. This circuit contains two gates, a single-qubit gate, and a multi-qubit gate, a Hadamard and CNOT, respectively.
The reason for choosing this was not random. In fact, this circuit has a name, the Bell state. The Bell state, which was originally described in a theoretical paper by John Bell in 1964, describes how there are four maximally entangled quantum states between two qubits that are in a superposition state. These four states are commonly referred to as the Bell states.
At this point, you may be wondering why this is so important. Well, if we can prepare qubits to a particular state, in this case, the maximally entangled state, this can help streamline the creation of various quantum circuits and algorithms. To learn more about this, let’s first prepare the four Bell states, and perhaps, along the way...