Two-axis control of a singlet-triplet qubit with an integrated micromagnet

摘要

The qubit is the fundamental building block of a quantum computer. Wefabricate a qubit in a silicon double quantum dot with an integratedmicromagnet in which the qubit basis states are the singlet state and thespin-zero triplet state of two electrons. Because of the micro magnet, themagnetic field difference $\Delta B$ between the two sides of the double dot islarge enough to enable the achievement of coherent rotation of the qubit'sBloch vector about two different axes of the Bloch sphere. By measuring thedecay of the quantum oscillations, the inhomogeneous spin coherence time$T_{2}^{*}$ is determined. By measuring $T_{2}^{*}$ at many different values ofthe exchange coupling $J$ and at two different values of $\Delta B$, we provideevidence that the micromagnet does not limit decoherence, with the dominantlimits on $T_{2}^{*}$ arising from charge noise and from coupling to nuclearspins.