Cryocharacterization of an integrated superconducting cavity for suspended carbon nanotube quantum dot readout

Abstract

Conventional transport measurements cannot detect charge transitions in carbon nanotube quantum dots when no net current flows, whereas existing dispersive readout approaches using separate chips suffer from parasitic capacitances and limited scalability. We developed the first fully integrated platform within our research group that capacitively couples a λ/4 niobium superconducting resonator (fr = 5.88 GHz, Qi = 1150, Qe = 1730) directly to a suspended carbon nanotube quantum dot, enabling cryogenic measurements from 10 mK to 6 K. We successfully demonstrated dispersive readout of interdot charge transitions that are invisible to transport techniques, while also observing clear Coulomb peaks, diamonds, and stability diagrams through reflectometry measurements. This integrated approach achieves higher signalto-noise ratios, precise control over resonance coupling, and eliminates wiring losses, establishing quantum non-demolition readout capabilities and opening new possibilities for charge qubit studies and electromechanical coupling experiments.