Continuous Variable Quantum Computing in Circuit QED

Continuous variables represent a new paradigm for quantum computing in which quantum information is encoded in the quadratures of an electromagnetic field, as opposed to qubit-based models. This field has recently received a lot of attention, mostly focusing on optical frequencies. To achieve universal quantum computation the generation of field states with negative Wigner function is highly desirable. However, deterministic generation of such states at optical frequencies is an experimental challenge, since the available nonlinear materials allows only for squeezing of incoming Gaussian states, leaving the Wigner function positive. In this work, we consider superconducting circuits, where the strong Josephson junction nonlinearity enables straightforward generation of non-Gaussian states. Using quantum trajectory methods, we explore the resonance fluorescence from a driven two-level atom in a 1D transmission line, with parameters compatible with current circuit-QED technology. We report on the parameter regimes resulting in outgoing field states with a negative Wigner function.