Control and Tomography of a Three Level Superconducting Artificial Atom

TL;DR

This paper demonstrates precise control and tomography of a three-level superconducting artificial atom (qutrit) using optimal control techniques, achieving high-fidelity state preparation and measurement.

Contribution

It introduces a method for preparing and characterizing arbitrary three-level states in a transmon superconducting qubit with high fidelity.

Findings

Achieved 96% average fidelity in state tomography.

Successfully prepared arbitrary superposition states.

Demonstrated full quantum state tomography of a transmon qutrit.

Abstract

A number of superconducting qubits, such as the transmon or the phase qubit, have an energy level structure with small anharmonicity. This allows for convenient access of higher excited states with similar frequencies. However, special care has to be taken to avoid unwanted higher-level populations when using short control pulses. Here we demonstrate the preparation of arbitrary three-level superposition states using optimal control techniques in a transmon. Performing dispersive read-out we extract the populations of all three levels of the qutrit and study the coherence of its excited states. Finally we demonstrate full quantum state tomography of the prepared qutrit states and evaluate the fidelities of a set of states, finding on average 96%.