Characterising Polariton States in Non-Dispersive Regime of Circuit Quantum Electrodynamics

TL;DR

This paper explores the formation and properties of polariton states in a superconducting qubit-resonator system operating outside the typical dispersive regime, providing experimental data and numerical validation.

Contribution

It experimentally characterizes polariton states in a non-dispersive superconducting circuit QED system and compares results with advanced numerical models.

Findings

Polariton states are formed in the non-dispersive regime.

Transition frequencies are modified by higher-level couplings.

Numerical results agree closely with experimental data.

Abstract

A superconducting qubit coupled to a read-out resonator is currently the building block of multiple quantum computing as well as quantum optics experiments. A typical qubit-resonator system is coupled in the dispersive regime, where the detuning between qubit and resonator is much greater than the coupling between them. In this work, we fabricated and measured a superconducting transmon-resonator system in the non-dispersive regime. The dressed states formed by the mixing of the bare qubit and resonator states can be further mixed by applying a drive on the qubit, leading to the formation of polariton states. We report experimental studies of transitions between polariton states at varying driving powers and frequencies and show how the non-dispersive coupling of the higher levels of the qubit-resonator system modifies the polariton eigenstates and the corresponding transition frequencies. We also report close agreement with numerical results obtained from a driven Jaynes-Cummings Model beyond the dispersive regime.