# Regensburg 2019 – wissenschaftliches Programm

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# TT: Fachverband Tiefe Temperaturen

## TT 10: Focus Session: New Bright Sources of Quantum Microwaves

### TT 10.3: Hauptvortrag

### Montag, 1. April 2019, 16:00–16:30, H2

**Quantum microwaves with a DC-biased Josephson junction** — Fabien Portier^{1}, Ambroise Peugeot^{1}, Chloé Rolland^{1}, Marc Westig^{1}, Gerbold Ménard^{1}, Yuri Mukharsky^{1}, Hélène le Sueur^{1}, Patrice Roche^{1}, Philippe Joyez^{1}, •Carles Altimiras^{1}, Patrice Bertet^{1}, Daniel Esteve^{1}, Denis Vion^{1}, Max Hofheinz^{1}, Pérola Milman^{2}, Bjoern Kubala^{3}, Simon Dambach^{3}, and Joachim Ankerhold^{3} — ^{1}SPEC (UMR 3680 CEA-CNRS), CEA Paris-Saclay, 91191 Gif-sur-Yvette, France — ^{2}LMPQ, Université Paris Diderot, CNRS UMR 7162, 75013, Paris, France — ^{3}ICQS and IQST, University of Ulm, 89069 Ulm, Germany

Tunneling of a Cooper pair through a dc-biased Josephson junction is possible only if collective excitations (photons) are produced in the rest of the circuit to conserve the energy. The probability of tunneling and photon creation, well described by the theory of dynamical Coulomb blockade, increases with the coupling strength between the tunneling charge and the circuit mode, which scales as the mode impedance. Using very simple circuits with only one or two high impedance series resonators, we first show the equality between Cooper pair tunneling rate and photon production rate. Then we demonstrate a blockade regime for which the presence of a single photon blocks the next tunneling event and the creation of a second photon. Finally, using two resonator with different frequencies, we demonstrate photon pair production, two-mode squeezing, and entanglement between the two modes leaking out of the resonators.