High-Energy Quasiparticle Injection into Mesoscopic Superconductors

Abstract

At nonzero temperatures, superconductors contain excitations known as Bogoliubov quasiparticles. The mesoscopic dynamics of quasiparticles inform the design of quantum information processors, among other devices. Knowledge of these dynamics stems from experiments in which quasiparticles are injected in a controlled fashion, typically at energies comparable to the pairing energy \cite{Levine1968,Smith1975,Ullom2000,Barends2008,Patel2017}. Here we perform tunnel spectroscopy of a mesoscopic superconductor under high electric field. We observe quasiparticle injection due to field-emitted electrons with $\mathbf{10^6}$ times the pairing energy, an unexplored regime of quasiparticle dynamics. Upon application of a gate voltage, the quasiparticle injection decreases the critical current and, at sufficiently high electric field, the field-emission current (< 0.1 nA) switches the mesoscopic superconductor into the normal state, consistent with earlier results \cite{DeSimoni2018}. We expect that high-energy injection will be useful for developing quasiparticle-tolerant quantum information processors, will allow rapid control of resonator quality factors, and will enable the design of electric-field-controlled superconducting devices with new functionality.