Simple pulses for elimination of leakage in weakly nonlinear qubits

TL;DR

This paper presents a simple, analytically derived control technique that significantly reduces leakage errors in weakly nonlinear qubits, enhancing quantum gate fidelity with smooth, feasible pulses.

Contribution

It introduces an easy-to-implement analytic formula adding a second control proportional to the first pulse's derivative to suppress leakage in weakly nonlinear qubits.

Findings

Reduces leakage error by an order of magnitude in superconducting qubits.

Uses smooth, feasible pulse shapes for practical implementation.

Shows weak anharmonicity is not a fundamental barrier for quantum gates.

Abstract

In realizations of quantum computing, a two-level system (qubit) is often singled out of the many levels of an anharmonic oscillator. In these cases, simple qubit control fails on short time scales because of coupling to leakage levels. We provide an easy to implement analytic formula that inhibits this leakage from any single-control analog or pixelated pulse. It is based on adding a second control that is proportional to the time-derivative of the first. For realistic parameters of superconducting qubits, this strategy reduces the error by an order of magnitude relative to the state of the art, all based on smooth and feasible pulse shapes. These results show that even weak anharmonicity is sufficient and in general not a limiting factor for implementing quantum gates.