Integrated Charge Sensing and Electromechanics in Suspended Carbon Nanotube Quantum Devices

Ultra-sensitive charge detection is a widely used tool for quantum electronics, with applications in quantum information processing and in probing the physics of condensed matter systems. Existing high-bandwidth approaches typically rely on impedance-matched resonant circuits, whose footprint and integration requirements can add complexity and constrain device scalability, despite recent advances towards compact on-chip implementations. In this work, we introduce a current-mode charge sensor in a suspended carbon nanotube, operating at the 1.25 MHz resonance of an RLC tank circuit and achieving a charge sensitivity of 0.15 microe/sqrt(Hz). We utilize it to measure a double quantum dot (DQD) electrostatically defined in the same nanotube, revealing a highly regular charge stability diagram. We perform single-shot readout of the DQD charge state at an integration time of 3.56 microseconds, without any false assignments over 10^7 measurements and a signal-to-noise ratio of 17 exceeding the state of the art. This readout scheme also provides a sensitive probe of the mechanical degree of freedom of the suspended nanotube, where mechanical displacement is transduced into conductance variations of the charge sensor, enabling measurements from driven nonlinear dynamics to thermomechanical motion at the few-phonon level while operating in a regime of strongly suppressed dynamical backaction