Derivation of the Biot-Savart equation from the Nonlinear Schrödinger equation

Abstract

We present a systematic derivation of the Biot-Savart equation from the Nonlinear Schrödinger equation, in the limit when the curvature radius of vortex lines and the inter-vortex distance are much greater than the vortex healing length, or core radius. We derive the Biot-Savart equations in Hamiltonian form with Hamiltonian expressed in terms of vortex lines, $$ H= \frac{κ^2}{8 π}\int_{|{\bf s}-{\bf s}'|>ξ_*} \frac{d{\bf s} \cdot d {\bf s}'}{|{\bf s}-{\bf s}'|} \,,$$ with cut-off length $ξ_* \approx 0.3416293 /\sqrt{ρ_0},$ where $ρ_0$ is the background condensate density far from the vortex lines and $κ$ is the quantum of circulation.