Fidelity and leakage of Josephson qubits

TL;DR

This paper investigates how higher energy states in Josephson qubits cause quantum leakage and fidelity loss, and proposes design strategies to minimize these errors for improved quantum gate performance.

Contribution

It demonstrates methods to reduce quantum leakage errors in Josephson qubits by optimized gate design and operation, addressing a key challenge in quantum hardware.

Findings

Higher charge states reduce gate fidelity.

Proper gate design minimizes leakage errors.

Strategies improve quantum gate accuracy.

Abstract

The unit of quantum information is the qubit, a vector in a two-dimensional Hilbert space. On the other hand, quantum hardware often operates in two-dimensional subspaces of vector spaces of higher dimensionality. The presence of higher quantum states may affect the accuracy of quantum information processing. In this Letter we show how to cope with {\em quantum leakage} in devices based on small Josephson junctions. While the presence of higher charge states of the junction reduces the fidelity during gate operations we demonstrate that errors can be minimized by appropriately designing and operating the gates.