Quantum Dynamics of a few-photon Microwave Parametric Oscillator

We experimentally investigate quantum dynamics of a non-linear superconducting RF resonator in the intermediate (n ~ 5) photon number regime. In particular, we study parametric processes induced by modulation of the resonator’s inductance to prepare non-classical photon states, which may be useful in future continuous-variable quantum error correction schemes. The system can be described as a Kerr parametric oscillator (KPO) with linewidth significantly smaller than the single photon Kerr shift. We observe narrowing of the linewidth when approaching the parametric stability threshold as well as non-classical signatures in the resonator state’s free evolution caused by the Kerr non-linearity. To read out the quantum state of the resonator, we developed a tomography method which utilizes its nonlinear character to estimate the system’s density matrix from the power spectrum of the field emitted by it.