Amplitude spectroscopy of two coupled qubits

TL;DR

This paper investigates how large amplitude, time-dependent driving fields influence two coupled qubits, revealing resonance conditions, transition probabilities, and interference patterns that depend on system parameters.

Contribution

It introduces a detailed analysis of resonant transitions in coupled qubits under strong driving using RWA and Floquet states, highlighting the role of coupling strength.

Findings

Resonance conditions include qubit coupling strength.

Interference patterns reveal system parameters.

Transition probabilities depend on quasi-energy states.

Abstract

We study the effect of a time-dependent driving field with a large amplitude on a system composed of two coupled qubits (two-level systems). Using the rotating wave approximation (RWA) makes it possible to find simple conditions for resonant excitation of the four-level system. We find that the resonance conditions include the coupling strength between the qubits. Numerical simulations confirm the qualitative conclusions following from the RWA. To reveal the peculiarities of resonant transitions caused by the quasi-level motion and crossing in a periodic driving field, we use Floquet states, which determine the precise intermediate states of the system. Calculating the quasi-energy states of the multi-level system makes it possible to find the transition probabilities and build interference patterns for the transition probabilities. The interference patterns demonstrate the possibility of obtaining various pieces of information about the qubits, since the positions of transition-probability maxima depend on various system parameters, including the coupling strength between the qubits.