Information, Quantum Computing, Physics.
4.1 — Alice and Bob’s Bell state, a shared entanglement between a qubit held by Alice (A1) and a qubit held by Bob (B1). So keeping count, we now have three qubits, two held by Alice (A0 and A1), and one held by Bob (B1). A1 and B1 we’ve prepared in an entangled state (Eq 4.1), and the state of A0