Elongated quantum dot as a distributed charge sensor

Increasing the separation between semiconductor quantum dots offers scaling advantages by facilitating gate routing and the integration of sensors and charge reservoirs. Elongated quantum dots have been utilized for this purpose in GaAs heterostructures to extend the range of spin-spin interactions. Here, we study a MOS device where two quantum dot arrays are separated by an elongated quantum dot (340 nm long, 50 nm wide). We monitor charge transitions of the elongated quantum dot by measuring radiofrequency single-electron currents to a reservoir to which we connect a lumped-element resonator. We operate the dot as a single-electron box to achieve charge sensing of remote quantum dots in each array, separated by an edge-to-edge distance of 480 nm. Charge detection on both ends of the elongated dot at a coinciding setpoint demonstrates that the charge states are well distributed across its nominal length, supported by the simulated quantum mechanical electron density. Likewise, we show elongated-peripheral quantum dot tunnel couplings can exceed $20\mathrm{GHz}$, above the electron temperature, fulfilling the requirement for mediated exchange. Our results illustrate how single-electron boxes can be realized with versatile footprints that may enable compact quantum processor layouts, offering distributed charge sensing in addition to the possibility of mediated coupling.