  The compound semiconductor gallium arsenide (GaAs) provides an ultra-clean
platform for storing and manipulating quantum information, encoded in the
charge or spin states of electrons confined in nanostructures. The absence of
inversion symmetry in the zinc-blende crystal structure of GaAs however,
results in strong piezoelectric coupling between lattice acoustic phonons and
electrons, a potential hindrance for quantum computing architectures that can
be charge-sensitive during certain operations. Here we examine phonon
generation in a GaAs double dot, configured as a single- or two-electron charge
qubit, and driven by the application of microwaves via surface gates. In a
process that is a microwave analog of the Raman effect, stimulated phonon
emission is shown to produce population inversion of a two-level system and
provides spectroscopic signatures of the phononic environment created by the
nanoscale device geometry.
