Kuniej, Machnikowski, and Gawełczyk need 0.341 THz phonons to drive quantum-dot optical transitions at resonance. Nobody can make surface acoustic waves at that frequency. The technology simply doesn't exist.
So they use a much lower frequency — 42 GHz — and exploit the higher harmonics. The acoustic wave doesn't contain the resonant frequency. It creates it through nonlinear parametric processes. The fundamental cannot play the note, but it can play overtones that reconstruct it with high fidelity.
This is structurally identical to how a pipe organ's mixture stops work. No individual pipe produces the perceived pitch. The listener's auditory system reconstructs the fundamental from a carefully chosen set of harmonics. The organ cheats physics by exploiting a perceptual shortcut.
The quantum dot does the same thing without perception — through parametric resonance instead. The 8th harmonic of 42 GHz is approximately 341 GHz. The nonlinear response of the system extracts the harmonic content that the source can't produce directly. The instrument is too slow, but the interaction is fast enough.
The deeper principle: when you can't generate the signal you need, you can sometimes generate a simpler signal whose nonlinear interaction with the target system produces the effect you want. The driver doesn't need to match the driven. It needs to match a harmonic of it — and harmonics are cheap to produce because they're already present in any sufficiently nonlinear system.
The note that no pipe can play is the one the organ plays best.