Tailoring population inversion in Landau-Zener-St\"uckelberg interferometry of flux qubits

TL;DR

This paper investigates how environmental interactions and circuit parameters influence population inversion in flux qubits under Landau-Zener-Stückelberg interference, enabling control over qubit states through circuit design.

Contribution

It demonstrates that population inversion can be achieved solely via environmental bath effects and shows how the resonant frequency of the measuring circuit can be used to control this inversion.

Findings

Population inversion can be mediated by the environment at long driving times.

The resonant frequency of the measuring circuit affects the asymptotic population of the qubit.

Tailoring the circuit's resonant frequency allows control over the degree of population inversion.

Abstract

We distinguish different mechanisms for population inversion in flux qubits driven by dc+ac magnetic fields. We show that for driving amplitudes such that there are Landau-Zener-St\"uckelberg intereferences, it is possible to have population inversion solely mediated by the environmental bath at long driving times. We study the effect of the resonant frequency $\Omega_p$ of the measuring circuit, finding different regimes for the asymptotic population of the state of the flux qubit. By tailoring $\Omega_p$ the degree of population inversion can be controlled. Our studies are based on realistic simulations of the device for the Josephson flux qubit using the Floquet-Born-Markov formalism.