Semiclassical limit of cubic nonlinear Schrödinger equations for mixed states
Daniel Han-Kwan, Frédéric Rousset
TL;DR
The paper proves a rigorous semiclassical limit for the cubic nonlinear Schrödinger equation with mixed states, showing convergence to a singular Vlasov equation with a force term proportional to $\nabla_x\rho_f$. The authors develop a robust framework based on the Wigner transform, introducing an extended Wigner system to manage high-order derivatives, and construct a parametrix that is a matrix-valued Fourier integral operator. A key innovation is the quantum averaging lemma, which provides a derivative gain in the averaging process and yields uniform-in-$\varepsilon$ bounds under a quantum Penrose stability condition. Under uniform weighted Sobolev bounds and Penrose stability (which holds for small data or certain Maxwellian-like perturbations), the Wigner solutions exist on a fixed time interval, remain controlled as $\varepsilon\to 0$, and converge to the unique solution of the singular Vlasov-Benney equation, thereby justifying the quantum-to-classical transition for mixed states in this setting.
Abstract
In this work, we study the semiclassical limit of cubic Nonlinear Schrödinger equations for mixed states. We justify the limit to a singular Vlasov equation (in which the force field is proportional to the gradient of the density), for data with finite Sobolev regularity whose velocity profiles satisfy a quantum Penrose stability condition. This latter condition is always satisfied for small data (with a smallness condition independent of the semiclassical parameter) both in the focusing and the defocusing case, and for small perturbations of a large class of physically relevant examples in the defocusing case, such as local Maxwellian-like profiles.
