Effects of higher levels of qubits on control of qubit protected by a Josephson quantum filter

TL;DR

This paper investigates how higher energy levels in a Josephson quantum filter and a data qubit affect quantum control, revealing that higher levels of the data qubit influence control accuracy while those of the filter do not.

Contribution

It provides a theoretical analysis of higher energy level effects on qubit control, identifying conditions to optimize control efficiency in superconducting quantum systems.

Findings

Higher levels of the data qubit cause resonance shifts and reduce excitation population.

Higher levels of the Josephson quantum filter do not significantly affect control.

Optimal pulsed field parameters are identified to maximize control efficiency.

Abstract

A Josephson quantum filter (JQF) protects a data qubit (DQ) from the radiative decay into transmission lines in superconducting quantum computing architectures. A transmon, which is a weakly nonlinear harmonic oscillator rather than a pure two-level system, can play a role of a JQF or a DQ. However, in the previous study, a JQF and a DQ were modeled as two-level systems neglecting the effects of higher levels. We theoretically examine the effects of the higher levels of the JQF and the DQ on the control of the DQ. It is shown that the higher levels of the DQ cause the shift of the resonance frequency and the decrease of the maximum population of the first excited state of the DQ in the controls with a continuous wave (cw) field and a pulsed field, while the higher levels of the JQF do not. Moreover, we present optimal parameters of the pulsed field, which maximize the control efficiency.