Observation of Multiphoton Frequency Conversion in Superconducting Circuits

TL;DR

This paper reports the experimental observation of multiphoton frequency conversion in superconducting transmon circuits driven by bichromatic microwaves, supported by Floquet simulations and graph theoretic analysis, demonstrating controllability of multiphoton processes.

Contribution

It introduces the first experimental realization of high-order multiphoton conversion in superconducting circuits with theoretical modeling and control strategies.

Findings

Successful observation of three-photon frequency conversion.

Floquet formalism effectively models quantum interferences.

Control over multiphoton processes across a wide frequency range.

Abstract

Multiphoton up/down conversion in a transmon circuit, driven by a pair of microwaves tuned near and far off the qubit resonance, has been observed. The experimental realization of these high order non-linear processes is accomplished in the three-photon regime, when the transmon is coupled to weak bichromatic microwave fields with the same Rabi frequencies. A many-mode Floquet formalism, with longitudinal coupling, is used to simulate the quantum interferences in the absorption spectrum that manifest the multiphoton pumping processes in the transmon qubit. An intuitive graph theoretic approach is used to introduce effective Hamiltonians that elucidate main features of the Floquet results. The analytical solutions also illustrate how controllability is achievable for desired single- or multiphoton pumping processes in a wide frequency range.