Summary

In this chapter, we have discussed some interesting applications of two-qubit systems, which have allowed us to deepen our understanding of these systems and have helped us illustrate how entanglement (in addition to superposition and interference) is used in quantum algorithms.

We began this chapter with superdense coding, a compact way of transmittingclassical information via quantum means; we saw how this protocol enables two parties to send two bits of classical data encoded in a single qubit. Then we introduced the CHSH game, which unraveled some of the hidden power of quantum entanglement. Both of these protocols assumed that the two communicating parties had each a qubit from a pair in a Bell state.

Lastly, we introduced Deutsch’s algorithm that allowed us to determine whether a one-bit Boolean function was constant or balanced using a single call to an oracle. This algorithm gave us a first glimpse into some ideas that we will reuse and further develop later in...