Quantum interference arises from the indistinguishability in principle, by precise measurement at a specified final time, of alternative sequences of states of a quantum system that begin with a given initial state and end with the corresponding final state. It is manifested, for example, in the two-slit interferometer and the double Mach-Zehnder interferometer discussed in Chapters 1 and 3, respectively. Most important, when the indistinguishability of alternatives for producing joint events arises, as in the latter apparatus, entanglement may be involved. Erwin Schrödinger, who first used the term “entanglement,” called entanglement “the characteristic trait of quantum mechanics” , , . The extraordinary correlation between quantum subsystem states associated with entanglement can be exploited by quantum computing algorithms using interference to solve computational tasks, such as factoring, far more efficiently than is possible using classical methods, as we show in later chapters. Entangled states are similarly exploitable by uniquely quantum communication protocols, such as quantum teleportation, superdense coding, and advanced forms of quantum key distribution, using local operations and classical communication (LOCC).
KeywordsEntangle State Pure State Bell State Quantum Entanglement Bell Inequality
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