Schrödinger dynamics in length-scale hierarchy: from spatial rescaling to Huygens-like proliferation of Gaussian wavepackets

Abstract

Abstract Studying possible laws, rules, and mechanisms of time-evolution of quantum wavefunctions leads to deeper understanding about the essential nature of the Schrödinger dynamics and interpretation on what the quantum wavefunctions are. As such, we attempt to clarify the mechanical and geometrical processes of deformation and bifurcation of a Gaussian wavepacket of the Maslov type from the viewpoint of length-scale hierarchy in the wavepacket size relative to the range of relevant potential functions. Following the well-known semiclassical view that (1) Newtonian mechanics gives a phase space geometry, which is to be projected onto configuration space to determine the basic amplitude of a wavefunction (the primitive semiclassical mechanics), our study proceeds as follows. (2) The quantum diffusion arising from the quantum kinematics makes the Gaussian exponent complex-valued, which consequently broadens the Gaussian amplitude and brings about a specific quantum phase. (3) The wavepacket is naturally led to bifurcation (branching), when the packet size gets comparable with or larger than the potential range. (4) Coupling between the bifurcation and quantum diffusion induces the Huygens-principle like wave dynamics. (5) All these four processes are collectively put into a path integral form. We discuss some theoretical consequences from the above analyses, such as (i) a contrast between the δ-function-like divergence of a wavefunctions at focal points and the mesoscopic finite-speed shrink of a Gaussian packet without instantaneous collapse, (ii) the mechanism of release of the zero-point energy to external dynamics and that of tunneling, (iii) relation between the resultant stochastic quantum paths and wave dynamics, and so on.