Tailored Electron-Phonon Interactions in Semiconductor Double Quantum Dots

Abstract

This thesis demonstrates the construction of a double quantum dot (DQD) in an Indium Arsenide (InAs) nanowire that is mechanically suspended in vacuum between metal contacts and capacitively coupled to a superconducting microwave resonator. This mechanical suspension scheme places the DQD at the center of an effective 380 nm long phonon cavity created by the contacts supporting the ends of the suspended nanowire. Because electron-phonon coupling mechanisms lead to electron transport through the DQD, measurements of current can be used as a probe of the phonon density of states in the nanostructure. Current measurements reveal strong signatures of electron-phonon coupling at energies corresponding to the guitar string vibrational modes of the suspended nanowire. In addition, photon emission has recently been observed in InAs nanowire DQDs coupled to superconducting cavities. However, it has been proposed that a phonon must simultaneously be emitted with each photon to ensure energy conservation. Therefore the photon emission rate should be enhanced when the emitted phonons couple strongly to electrons in the DQD. We quantitatively confirm this hypothesis by independently measuring both the photon emission into the cavity and the electron-phonon coupling strength as a function of the DQD energy splitting.