Coherent-state overcompleteness, path integrals, and weak values

Abstract

In the Hilbert space of a quantum particle the standard coherent-state resolution of unity is written in terms of a phase-space integration of the outer product zz. Because no pair of coherent states is orthogonal, one can represent the closure relation in non-standard ways, in terms of a single phase-space integration of the “unlike” outer product z′z, z′≠z. We show that all known representations of this kind have a common ground and that our reasoning extends to spin coherent states. These unlike identities make it possible to write formal expressions for a phase-space path integral, where the role of the Hamiltonian H is played by a weak energy value Hweak. Therefore, in this context, we can speak of weak values without any mention to measurements. The quantity Hweak appears as the ruler of the phase-space dynamics in the semiclassical limit.