  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 .
Here we perform tunnel spectroscopy of a mesoscopic superconductor under high
electric field. We observe quasiparticle injection due to field-emitted
electrons with 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. 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.
