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Gate reflectometry for CMOS qubit readout



The development of sensitive and compact readout tools of quantum states is a central issue in the run to industrial scalability of semiconductor quantum bits (qubits). We employ the gates of industrial silicon Field-Effect Transistors (used as qubits) as radio-frequency resonators integrated in the qubit architecture.

Published on 28 June 2017
At mK temperatures, such gates induce and tune an electron double quantum dot, the typical platform to realize a spin qubit. By radio-frequency reflectometry these same gates probe key features of the double quantum dot, like its spectrum and charge relaxation rates. Indeed the gate capacitance contains a measurable quantum contribution, sensitive to the (spin dependent) local density of states.
Through a collaboration between INAC, LETI and the University of Notre-Dame (Indiana) we demonstrate simultaneous gate-based radio-frequency readout in a prototypal device for qubit operations. This study promotes reflectometry as a technique of choice for quantum readout in multiqubit structures.

Figure a. Double gate Si transistor. Either of the gates is connected to a lumped inductor, which, through a capacitance Cp, constitutes the resonator. Specific electronics at 4.2K and 300K amplifies and down-converts the reflected signal.
Figure b. Diagram of the phase signal by Gate2, displaying all the charge transitions of the double dot. These transitions happen as the electronic states in both dots are aligned (red-blue diagonal lines) and as the ground state in each dot is aligned with the Fermi energy in the source and drain (blue lines running -almost- parallel to the axis).

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