Microwave-driven coherent operations of a semiconductor quantum dot charge qubit

TL;DR

This paper demonstrates high-fidelity, microwave-driven coherent control of a semiconductor charge qubit in a double quantum dot, achieving fast Rabi oscillations and robust operations at the sweet spot.

Contribution

It introduces microwave driving for charge qubits, enabling high-speed, high-fidelity control while maintaining protection at the sweet spot, surpassing previous dc pulse methods.

Findings

Achieved Rabi frequency up to 2 GHz.

Process fidelities greater than 86%.

Coherent control at the sweet spot with microwave driving.

Abstract

A most intuitive realization of a qubit is a single electron charge sitting at two well-defined positions, such as the left and right sides of a double quantum dot. This qubit is not just simple but also has the potential for high-speed operation, because of the strong coupling of electric fields to the electron. However, charge noise also couples strongly to this qubit, resulting in rapid dephasing at nearly all operating points, with the exception of one special 'sweet spot'. Fast dc voltage pulses have been used to manipulate semiconductor charge qubits, but these previous experiments did not achieve high-fidelity control, because dc gating requires excursions away from the sweet spot. Here, by using resonant ac microwave driving, we achieve coherent manipulation of a semiconductor charge qubit, demonstrating a Rabi frequency of up to 2GHz, a value approaching the intrinsic qubit frequency of 4.5GHz. Z-axis rotations of the qubit are well-protected at the sweet spot, and by using ac gating, we demonstrate the same protection for rotations about arbitrary axes in the X-Y plane of the qubit Bloch sphere. We characterize operations on the qubit using two independent tomographic approaches: standard process tomography and a newly developed method known as gate set tomography. Both approaches show that this qubit can be operated with process fidelities greater than 86% with respect to a universal set of unitary single-qubit operations.