Figure 1: Experimental apparatus.
From: Suppressing qubit dephasing using real-time Hamiltonian estimation
(a) A scanning electron microscope image of the double QD with a schematic of the apparatus used for adaptive qubit control. A floating metal gate protruding from the right can be seen which increases the capacitance between the qubit and an adjacent qubit (not pictured), which is left inactive for this work. The reflected read-out drive signal is demodulated to DC, digitized by a correlated double sampler (CDS), and ΔBz is estimated in real time by the field-programmable gate array (FPGA). The FPGA updates the digital to analogue converter (DAC) to keep the voltage controlled oscillator (VCO) resonant with the estimated value of ΔBz. The VCO controls the voltage detuning, ε(t) between the QDs, which, in turn, modulates J at ΩJ. (b) The Bloch sphere representation for the S−T0 qubit showing the two axes of control, J and ΔBz.
