Lecture 5. Multiqubit operations

We have discussed the basic operations that are under concern for multi-qubit systems. It is possible to prepare entangled states, including Bell states, on multi-qubit systems. Entangled states can be prepared, for example, using multiqubit unitary operations. Measurements of some of the qubits can be performed, and non-destructive measurements can be reduced to ancillae measurements. It is interesting to consider quantum and classical control operations, which are related by the deferred measurement principle. A quantum circuit is some composition of the above operations. Problems efficiently solvable using quantum circuits lie in the complexity class $\mathtt{BQP}$.