Fig. 4: CPMG experiments.
From: Charge-noise spectroscopy of Si/SiGe quantum dots via dynamically-decoupled exchange oscillations
a Schematic of the CPMG pulse sequence. The qubit is prepared along the x-axis and evolves under exchange for a total time τ + δt, during which we periodically apply composite X gates. b β versus J extracted from fits of the echo amplitude decay (left axis) and \({T}_{2}^{e}/{T}_{2}^{* }\) (right axis) versus J. Error bars represent the standard error of the fit for β. c Plot of \(\xi (\bar{\beta })\) (left axis) and R (right axis) versus \(\left|dJ/d\epsilon \right|\). The \(\xi (\bar{\beta })\) data are well fit to a straight line with a y-intercept of zero (black line), which is consistent with a charge-noise spectrum of the form \(S=A/{f}^{\bar{\beta }}\). d Plot of the normalized amplitude of the CPMG oscillations as a function of τ for select CPMG experiments. e\({T}_{2}^{{n}_{\pi }}\) (left axis) and the ratio \({T}_{2}^{{n}_{\pi }}/{T}_{2}^{* }\) (right axis) as a function of nπ.
