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

摘要

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