Fig. 2: Tunnel junction as a tunable quantum absorber.
From: Quantum bath engineering of a high impedance microwave mode through quasiparticle tunneling
a Quasiparticle tunneling induces an extra loss γn (Eq. (2)), which is different for each Fock state of the mode coupled to the junction. Dashed vertical lines show the onset of the l photon absorption process, given by (2Δ − lℏω)/e. The photon number n corresponding to the lowest Fock state with increased loss can be chosen with the bias voltage. The parameters correspond to the ones expected in the experiment. b Experimental spectroscopy of the 6 GHz mode as a function of the bias voltage V. The image shows the measured reflection coefficient ∣S11∣2 for an incident power of −115 dBm on the resonator. The onset of the different absorption processes is clearly visible up to l = 4.
