# Regensburg 2019 – wissenschaftliches Programm

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# DY: Fachverband Dynamik und Statistische Physik

## DY 16: Quantum Dynamics, Decoherence and Quantum Information

### DY 16.3: Vortrag

### Dienstag, 2. April 2019, 10:30–10:45, H6

**Entanglement via dissipation in a nonlinear circuit QED system** — •Dominik Maile^{1,2}, Sabine Andergassen^{1}, Wolfgang Belzig^{2}, and Gianluca Rastelli^{2} — ^{1}Eberhard Karls University, Tübingen, Germany — ^{2}University Konstanz, Konstanz, Germany

We discuss a superconducting nanoscale circuit formed by two microwave cavities coupled via a Josephson junction and a joint capacitance to the ground. In addition, the Josephson junction is shunted by a resistance and one plate of the capacitor is in series with a resistance connected to the ground. Such a configuration leads to dissipation in the relative phase difference across the Josephson junction and in the total charge of the two capacitances in parallel [1,2]. We show that, in the steady state, the resonators are in an entangled state and calculate the logarithmic negativity as a measure of entanglement in the harmonic regime. We find that the entanglement grows by increasing both dissipative coupling strengths via simultaneous squeezing of the fluctuations of the total charge and the relative phase difference. Due to the dissipative interaction, the system is not in a pure state. However, in the limit of large squeezing we compare the entanglement generated via dissipation with the one of an effective pure two-mode squeezed state. Increasing the coupling strength between the two oscillators via the Josephson energy also leads to a rise of the entanglement. Here the system enters the nonlinear coupling regime. We analyze the effect of such nonlinear interaction perturbatively.

[1] G. Rastelli, New Journal of Physics 18, 053033 (2016)

[2] D. Maile, et al. PRB 97, 155427 (2018)