Rabi-like oscillations of an anharmonic oscillator: classical versus quantum interpretation

TL;DR

This study observes Rabi-like oscillations in a Josephson device, analyzing the transition from quantum to classical behavior as excitation amplitude increases, and highlighting persistent quantum interferences.

Contribution

It demonstrates the classical and quantum interpretations of Rabi-like oscillations in an anharmonic oscillator, with detailed analysis of multi-level dynamics and quantum interferences.

Findings

Rabi-like oscillations observed in a Josephson device with enhanced coherence

Quantum behavior evident in Rabi frequency for up to 3 levels

Classical and quantum predictions converge at high excitation amplitudes

Abstract

We have observed Rabi-like oscillations in a current-biased dc SQUID presenting enhanced coherence times compared to our previous realization \cite{Claudon_PRL04}. This Josephson device behaves as an anharmonic oscillator which can be driven into a coherent superposition of quantum states by resonant microwave flux pulses. Increasing the microwave amplitude, we study the evolution of the Rabi frequency from the 2-level regime to the regime of multilevel dynamics. When up to 3 levels are involved, the Rabi frequency is a clear signature of quantum behavior. At higher excitation amplitude, classical and quantum predictions for the Rabi frequency converge. This result is discussed in the light of a calculation of the Wigner function. In particular, our analysis shows that pronounced quantum interferences always appear in the course of the Rabi-like oscillations.