The ubiquitous low energy excitations in amorphous and disordered crystalline dielectrics dominate the thermal, acoustic, and dielectric properties at low temperatures. They are thought to originate from atomic tunneling of single atoms or a group of atoms between two equilibrium positions at low temperatures. The interactions of these excitations with acoustic waves and electromagnetic field limit the quality factor of both nanomechanical and superconducting microwave resonators. They are a source of noise and decoherence in superconducting circuits, such as superconducting quantum bits (qubits), photo detectors, quantum motion sensors, and SQUID multiplexers.

We are interested in understanding the origin of these low energy excitations in dielectric thin films and finding ways to remove them in applications. The research work will involve studying the elastic (internal friction and speed of sound) and thermal (thermal conductivity and specific heat) properties of amorphous dielectric thin films at low temperatures (20mK to 30K). These measurements will be combined with structural characterizations, such as Raman spectroscopy, high resolution cross-section transmission electron microscopy, and X-ray diffraction, to classify the amorphous structure at nanometer length scales. We will also try to look for possible connection of the low energy excitations to other general properties of amorphous solids, such as glass transition and rigidity percolation. The fundamental science questions we seek to answer are (1) what parameters govern the macroscopic properties of amorphous solids? (2) do ideal amorphous solids without defects exist?

The research work offers opportunity to use a variety of nanofabrication tools, such as thin film deposition (electron-beam evaporation, sputtering, plasma-enhanced chemical vapor deposition), photolithography, electron beam lithography, reactive ion etching, wet chemical etching, SEM. The work also offers opportunity to use helium-3 cryostat and dilution refrigerators down to 20 mK and in 10T magnetic field.

 

key words

Superconducting quantum bit; Amorphous dielectrics; Thin films; Internal friction; Mechanical resonator; Phonon scattering Atomic tunneling states; Cryogenics; Electron beam evaporation;

Citizenship:  Open to U.S. citizens and permanent residents

Level:  Open to Postdoctoral applicants