Wave dislocation lines threading interferometers
In interferometers where a wave is divided into two beams that propagate along separate branches before being recombined, the closed circuit formed by the two branches must be threaded by wave dislocation lines. For a large class of interferometers, it is shown that the (signed) dislocation number, defined in a suitable asymptotic sense, jumps by +1 as the phase difference between the beams increases by 2 π . The argument is based on the single-valuedness of the wave function in the branches and leaking between them. In some cases, the jumps occur when the phase difference is an odd multiple of π . The same result holds for the Aharonov–Bohm wave function, where the waves passing above and below a flux line experience different phase shifts; in this case, where the wave is not concentrated onto branches, the threading dislocations coincide with the flux line.