Fig. 2: Cavity-enabled qubit-phonon absorption (CEQA).
From: Single-photon induced instabilities in a cavity electromechanical device
a The top panel depicts the pump (shown in red) and probe (shown in green) scheme for the CEQA experiment. The states \(\left\vert+, m\right\rangle\) denote one excitation in the polariton mode, along with m excitations in the mechanical resonator. The lower panel schematically illustrates operating points for the CEQA experiment in both devices. The red star represents the operating point in Device-1, indicating weak nonlinearity in the polariton mode. The blue star represents the operating point in Device-2, indicating strong nonlinearity. b Measurement of ∣S21∣ in the absence of the pump signal, showing the linear response of the polariton mode. The solid-black line is a Lorentzian fit to the response. c In the presence of a pump signal, an absorption feature appears in the probe transmission. At B∥ ~ 27 mT, the polariton mode frequency is set to ω+/2π ~ 5.884 GHz. The applied pump strength is Pi = −19 dBm, which corresponds to mean photon occupation of (5.80 ± 0.07) × 10−2, and the probe signal is 6 dB smaller than the pump. The solid black curve is the fitted curve yielding a single-photon coupling rate g+/2π ~ 40.0 ± 5.5 kHz. d Experimentally determined g+ for three different values of the applied magnetic field B∥. While increasing B∥, the flux-responsivity is nominally kept constant by adjusting B⊥. The error represents the statistical uncertainty. The dashed line represents a linear fit. e The absorption feature arising in the probe transmission of a strongly nonlinear mode in Device-2. The mode frequency is chosen to be ω+/2π ~ 6.005 GHz, which corresponds to a qubit detuning of \(({\omega }_{q}-{\omega }_{c})/2\pi \sim 120\) MHz. An analytical formula derived for a two-level system coupled to a mechanical resonator is used to fit the data, yielding the solid black curve.
