Microwave controlled Josephson junctions

Kazuhiro Yoshida, K. Hamasaki, Fumi Irie +1 more

Yoshihiro Shimazu, Y. Saito, Z. Wada

A double-loop four-Josephson-junction (4-JJ) flux qubit has an advantage over a three-Josephson-junction flux qubit in that the energy gap Δ at the symmetry point can be controlled in situ by varying the magnetic flux in one of the two loops. We report the results of a microwave spectroscopy measurement of a 4-JJ qubit. The magnetic fluxes in the two loops were controlled via a magnetic field and control flux. The excitation energy spectra at various values of control flux indicate the tunability of Δ via the control flux. Two branches of the excitation spectra were observed.

Orest G. Vendik, I. S. Danilov

The equivalent parameters of a Josephson junction in a microwave SQUID structure are calculated on the basis of relations obtained as a result of an analysis of the operation of an rf SQUID. This analysis is based on the sawtooth variation of the voltage on the resonator as a function of the constant flux bias. The quantitative characteristics permit regarding the Josephson junction as a linear impedance in the rf or microwave circuit, whose real and imaginary parts are controlled by the constant magnetic flux passing through the SQUID loop.

Johann Heyen Hinken

Jun Ma, P. H. Ouyang, Yaqiang CHAI +3 more

Elastic scattering is one of the useful methods to control the transmission behaviors of microwave photons transporting in microwave quantum networks without energy consumption. Therefore, it is of practical significance for developing microwave quantum devices and constructing multi-node microwave quantum networks. The transmission line embedded by a single Josephson junction can be described by different circuit models (series and parallel). In this work, we first theoretically analyze the transmission characteristics of microwave photons scattered by different elastic scattering models described by series or parallel embedding models, generated by a single LC loop or a nonlinear Josephson junction device, respectively. The classical microwave transport theory predicts that the series LC loop and the parallel LC loop lead to different elastic scattering behaviors of microwave photons, i.e. the series LC circuit yields the resonant reflection and the parallel LC circuit leads alternatively to the resonant transmission. Recently, the transport properties of microwave photons scattered by a Josephson junction embedded in a transmission line have been discussed, and the results suggested that the Josephson junction embedded in the transmission line can be described by a series embedding circuit, which implies the resonant reflection. We argue here that if the Josephson junction is embedded in parallel in the transmission line, the elastically scattered microwave photons should be transmitted by resonant transmission. In order to test which of the above two different embedding circuit models yielding the completely different elastic scattering behaviors, is physically correct, we then fabricate such a device, i.e. a single Joseph junction device embedded in a transmission line, and measure its elastic scattering transmission coefficient at an extremely low temperature. The results are consistent with the expected effect of the parallel embedding circuit model, but inconsistent with the behaviors predicted by the series embedding circuit model in the literature. According to the above theoretical and experimental analyses of the elastic scattering of a single Josephson junction device, we further propose a scheme to control the elastic scattering behavior of microwave photons by modulating a DC superconducting quantum interference device with a bypass current, which can be applied to the construction of a microwave quantum network based on elastic scattering node controls.

P. Russer