Fig. 3: Large amplitude phonon states observed through qubit ringdown dynamics.
From: Generation of large amplitude phonon states in quantum acoustics
a Schematic of the energy levels for the weakly hybridized phonon-qubit system. The qubit acts as an artificial two-level atom, with ground state \(\left\vert g\right\rangle\) and excited state \(\left\vert e\right\rangle\). A coherent drive of strength Ωq drives the qubit between its ground and excited state. The qubit-mechanical couple at a rate gqb and a qubit and mechanics decay at a rate γq and γb, respectively. The rate at which excitation transfer processes \(\left\vert e,N-1\right\rangle \to \left\vert g,N\right\rangle\) occur scales as \(\sqrt{N}\), where N is the total number of excitations, while the phonon relaxation scales linearly with N. The qubit is rapidly re-excited for strong pump powers, resulting in a build-up of phonon excitations. b Measured qubit ringdown for a qubit drive of −3.0 dBm. Blue line: the qubit drive is detuned from the HBAR by 250 kHz with the phonon mode in the non-lasing state, decaying on a time scale of the ~200 ns decay of the qubit. Red line: The qubit drive is tuned directly on resonance with the HBAR mode, exciting it into the lasing state, exhibiting a dramatically longer, non-exponential decay due to re-excitation from the coherently excited phonon mode. The master equation simulation (dashed black line) is plotted over the data.
