8.2 Entanglement
We’ve now seen many gate operations we can apply to a single qubit to change its state. In section 2.5, we worked through how to use classical logic gates to build a circuit for addition. qubit$entanglement
While we can apply not to a single bit, all the other operations require at least two bits for input. In the same way, we need to work with multiple qubits to produce interesting and useful results.
8.2.1 Moving from one to two qubits
We represent the states of a single qubit by vectors of length 1 in C2. We consider any two states equivalent if they differ only by multiplication by a complex unit. This is what we mean when we say that the states are “equal up to a global phase.” phase$global global phase
Each qubit starts by having its own associated copy of C2. When we have a quantum system with two qubits, we do not consider their collective states in a single C2 instance. Instead, we use...
