He regretted that name soon enough, when the IBM marketing department featured his work in an advertisement with the line “Stand by: I’ll teleport you some goulash.” But the name stuck, because teleportation worked. Alice does not send goulash; she sends qubits.3 The qubit is the smallest nontrivial quantum system. Like a classical bit, a qubit has two possible values, zero or one—which is to say, two states that can be reliably distinguished. In a classical system, all states are distinguishable in
