Measurement of Thermomechanical Motion in the Few-Phonon Regime Using Carbon Nanotube Charge Sensors

Abstract

We report the detection of thermomechanical motion in suspended carbon nanotube (CNT) resonators operating in the few-phonon regime, using an integrated charge sensor at cryogenic temperatures. We fabricate ultra-clean single-walled CNTs using a chemical vapor deposition (CVD) method and suspend them across predefined gate and electrode structures. The devices allow confinement of single and double quantum dots electrostatically defined in a CNT and capacitively coupled to a nearby charge sensor quantum dot. A radiofrequency (RF) readout circuit enables sensitive detection of thermomechanical motion at mode temperatures as low as 50 mK, corresponding to an average phonon occupation number below 10. We observe Lorentzian power spectral densities of the mechanical resonance and track the evolution of displacement amplitude with temperature. Deviations from ideal thermal scaling suggest additional temperature-dependent effects not fully captured by charge sensor sensitivity alone. These results aim to improve quantum nanomechanical sensing.