Seminars And Colloquia Next Week

Phononic frequency combs (PFC) are the mechanical analogs of celebrated photonic frequency combs. These represent a newly documented physical phenomenon in the well researched physical domain of mechanical resonators [1]. The emergence of PFC is mediated by nonlinear modal coupling. Through a series of experiments using micromechanical resonators, various physical features of phononic frequency combs have been identified. These include drive parameters for comb operation, hysteresis for comb spectrum tailoring and nonlinear sensitivity to physical perturbations. My talk will describe the physics of phononic frequency combs and will emphasize how these combs could be foundational to the fields of materials science, molecular science and chemical science. In that respect, I will present our first conceptual demonstrations of material combs, molecular combs and chemical combs respectively. I will also showcase our recent demonstration of broadband phononic combs using optical tweezers [2]. The future work will be focused on the applications of phononic frequency combs in sensing, communications and quantum information science.

1. Ganesan, A., Do, C. and Seshia, A., 2017. Phononic frequency comb via intrinsic three-wave mixing. Physical review letters, 118(3), p.033903.

2. de Jong, M.H., Ganesan, A., Cupertino, A., Gröblacher, S. and Norte, R.A., 2023. Mechanical overtone frequency combs. Nature Communications, 14(1), p.1458.

Topological superconductors provide a promising route to fault-tolerant quantum computing; however, it proved hard to find or engineer them. Recently, topological superconductivity was predicted to arise at the interface between quantum Hall and conventional superconducting states. Since both ingredients are readily available in the lab, topological superconductivity seemed to be within the reach. The predictions, however, focus on the idealized “clean” case, whereas only strongly disordered superconductors are compatible with high magnetic fields needed for the quantum Hall effect. Can topological superconductivity survive the presence of disorder?

We develop a theory of two counter-propagating quantum Hall edge states coupled via a narrow disordered superconductor. We show that, in contrast to the clean-case predictions, the edge states do not turn into a topological superconductor. Instead, the disorder tunes them to the critical point between the trivial insulating phase and the topological phase. We determine the manifestations of this criticality in the charge transport, finding that the critical conductance is a random, sample-specific quantity with a zero average and unusual bias dependence. The developed theory of disordered superconductor-quantum Hall interfaces offers an interpretation of recent experiments.

TBA