Induced transitions in non-Hermitian spin-boson models with time-dependent boundaries

TL;DR

This paper explores a non-Hermitian spin-boson model with time-dependent boundaries, revealing how boundary motion and parameter variation induce and control quantum transitions through a Hermitian mapping.

Contribution

It introduces a time-dependent Dyson map with squeezing to relate a non-Hermitian model to a Hermitian one with moving boundaries, enabling transition control.

Findings

Boundary motion opens transition channels forbidden in fixed-boundary models.

Constant squeezing leads to zero first-order transition amplitude.

Varying non-Hermitian parameters allows suppression or enhancement of transitions.

Abstract

We study a time-dependent non-Hermitian extension of the Sch\"utte-Da~Provid\^encia spin-boson Hamiltonian with complex couplings. A time-dependent Dyson map containing a squeezing transformation maps the model, in an admissible bounded regime, to a Hermitian Hamiltonian with real instantaneous energy spectrum. The squeezing contribution generates a dilatation term allowing the Hermitian partner to be interpreted as a fixed-domain representation of a system with moving boundaries. While the fixed-boundary Hermitian model conserves $Q=N-S_0$ and forbids transitions between sectors differing by two bosonic quanta, the boundary motion opens such channels. For closed boundary protocols with constant background parameters the first-order integrated transition amplitude vanishes, reflecting the unitary nature of constant squeezing. Nontrivial transition control arises when the non-Hermitian parameter varies during the boundary motion, changing the dressed basis and allowing boundary-induced transitions to be suppressed or enhanced by coherent interference.