Characterization of high-fidelity Raman qubit gates

TL;DR

This paper introduces a rapid tomographic method to accurately measure small errors in high-fidelity Raman qubit gates, leveraging their Morris-Shore symmetry and error amplification through repeated gate operations.

Contribution

A novel, efficient technique for quantifying errors in Raman qubit gates with Morris-Shore symmetry, enhancing precision in quantum gate characterization.

Findings

The method accurately measures small gate errors.

Error amplification enables high-precision error detection.

Applicable to gates with Morris-Shore symmetry.

Abstract

Raman qubits, represented by two ground or metastable quantum states coupled via an intermediate state, hold some advantages over directly coupled qubits, most notably much longer radiative lifetimes, shorter gate duration and lower radiation intensity due to using electric-dipole allowed optical transitions. They are also relatively simple to implement and control, making them an attractive option for building quantum gates for quantum computers. In this work, we present a simple and fast tomographic method to measure the errors of Raman qubit gates possessing the Morris-Shore dynamic symmetry. The latter occurs when the qubit states are on two-photon resonance and the driving fields have the same time dependence. The method is based on repeating the same gate multiple times, which amplifies the small coherent errors to sufficiently large values, which can be measured with high accuracy and precision. Then the (small) gate errors can be determined from the amplified errors by using the analytical connections between them.