Adiabatic modulation of driving protocols in periodically driven quantum systems

Abstract

We consider a periodically driven system where the high-frequency driving protocol consists of a sequence of potentials switched on and off at different instants within a period. We explore the possibility of introducing an adiabatic modulation of the driving protocol by considering a slow evolution of the instants when the sequence of potentials is switched on/off. We examine how this influences the long-term dynamics of periodically driven quantum systems. By assuming that the slow and fast timescales in the problem can be decoupled, we derive the stroboscopic (effective) Hamiltonian for a four-step driving sequence up to the first order in perturbation theory. We then apply this approach to a spin-$1/2$ system, where the adiabatic modulation of the driving protocol is chosen to produce an evolving emergent magnetic field that interacts with the spin. We study the emergence of diabolical points and diabolical loci in the parameter space of the effective Hamiltonian. Further, we study the topological properties of the maps of the adiabatic paths in the parameter space to the eigenspace of the effective Hamiltonian. In effect, we obtain a technique for tuning the topological properties of the eigenstates by selecting different adiabatic evolutions of the driving protocol, characterized by distinct paths in parameter space. This technique can be applied to any periodic driving protocol to achieve desirable topological effects.