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

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Màster Oficial de Ciència i Tecnologia Quàntiques / Quantum Science and Technology, Facultat de Física, Universitat de Barcelona. Curs: 2024-2025. Tutors: Stefan Forstner, Adrian Bachtold

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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.

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Màster Oficial - Ciència i Tecnologia Quàntiques / Quantum Science and Technology

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