The Enigma of Quantum Interference

Abstract

Quantum interference occurs when an initial state of a quantum system coherently evolves to a final state through two or more unobserved pathways in space or time. Such phenomena pose profound problematic issues within the framework of classical physics, especially when they emerge from sequential observations of individual, randomly emitted, noninteracting particles. A particularly striking example, proposed by the author and implemented at the Hitachi Advanced Research Laboratory, is the buildup of an electron interference pattern one electron at a time. Another example, the Aharanov-Bohm (AB) effect, involves the influence of a confined magnetic field — i.e. one through which particles do not pass—on the interference of electron wave functions. Although macroscopic quantum interference occurs in large-scale coherent systems like superfluids, superconductors, and Bose-Einstein condensates, the author shows that there can be no such interference in large-scale incoherent systems like “Schrödinger’s cat”.