Qubits and vibrations in suspended carbon nanotubes

Carbon nanotubes can be made with both low electronic disorder and low hyperfine coupling, making them attractive for studying qubits and mechanics in clean one-dimensional devices. I will describe the first qubit in this material, the spin-valley qubit. This makes use of both the electron spin and the valley magnetic moment, coupled by spin-orbit interaction. To realize this qubit, we defined a double quantum dot using gate potentials. Then we made use of the Pauli exclusion principle to configure the device as an electrical spin filter. Finally, we exploited a bend in the nanotube to manipulate the qubit electrically, reading it out and characterizing its coherence properties via the current through the device. Throughout this work, we made use of the technology of stamping, which allows low-disorder nanotubes to be incorporated into quantum dot devices.
In the second part of the talk, I will present electromechanical measurements of a suspended vibrating nanotube. Nanotube resonators combine low mass (leading to large zero-point motion) and high stiffness (leading to large mode spacing), making them potentially interesting for studying the quantum limit of mechanical motion. Until now, nearly all measurements relied on electrical transport through the device. I will show optomechanical measurements of nanotube motion, using a vibrating nanotube and a radio-frequency cavity tuned into resonance, and discuss how we may build on these experiments to study quantum mechanical effects