On a Class of Time-Dependent Non-Hermitian Hamiltonians

TL;DR

The paper addresses the challenge of time-dependent non-Hermitian quantum systems by showing that a TD unitary transformation F(t) can map H(t) to a time-independent pseudo-Hermitian form H0PH, which is related to a Hermitian Hamiltonian h via a Dyson map rho. This leads to a consistent tilde_eta inner product tilde_eta(t) = F† eta F that preserves unitarity and simplifies the computation of uncertainties. The authors derive uncertainty relations in the pseudo-Hermitian framework and prove their invariance under the transformation to the Hermitian picture. As a concrete application, they study a TD-mass particle in a complex TD linear potential, obtaining two time-independent pseudo-Hermitian Hamiltonians corresponding to a harmonic oscillator and an inverted oscillator, with exact squeezed-state solutions and a real, physically meaningful uncertainty bound in the HO case.

Abstract

We study a class of time-dependent (TD) non-Hermitian Hamiltonians $H(t)$ that can be transformed into a time-independent pseudo-Hermitian Hamiltonian $\mathcal{H}_{0}^{PH}$ using a suitable TD unitary transformation $F(t)$. The latter can in turn be related to a Hermitian Hamiltonian $h$ by a similarity transformation, $h=ρ\mathcal{H}_{0}^{PH} ρ^{-1}$ where $ρ$ is the Dyson map. Accordingly, once the Schrödinger equation for the Hermitian Hamiltonian $h$ is solved, the general solution of the initial system can be deduced. This allows to define the appropriate $\tildeη(t)$-inner product for the Hilbert space associated with $H(t)$, where $\tildeη(t)=F^{\dagger}(t)ηF(t)$ and $η=ρ^{\dagger}ρ$ is the metric operator. This greatly simplifies the computation of the relevant uncertainty relations for these systems. As an example, we consider a model of a particle with a TD mass subjected to a specific TD complex linear potential. We thus obtain two Hermitian Hamiltonians, namely that of the standard harmonic oscillator and that of the inverted oscillator. For both cases, the auxiliary equation admits a solution, and the exact analytical solutions are squeezed states given in terms of the Hermite polynomials with complex coefficients. Moreover, when the Hermitian Hamiltonian is that of the harmonic oscillator, the position-momentum uncertainty relation is real and greater than or equal to $\hbar/2$, thereby confirming its consistency.