FIGURE 3. PHASE ENGINEERING.
Quantum mechanical particles experience magnetic fields by acquiring Aharonov–Bohm (AB) phases. (a) In an AB interferometer, a magnetic field B is confined to the interior of a solenoid and is zero outside it. Nevertheless, a particle that travels on opposite sides of the solenoid will acquire a phase difference proportional to the enclosed magnetic flux Φ. That flux equals the line integral of the vector potential A around the solenoid. The charge is specified by q. (b) Particles that tunnel in a lattice experience an applied magnetic field in much the same way as in the AB effect. Their tunneling motion from one site to another acquires a so-called Peierls phase, such that the sum of the phases around a closed loop equals the enclosed flux.