Double superconductivity

S. Koka, Keshav Narain Shrivastava

David S. Simon

Hui Wang, Rui Wang, Daichi Sugiyama +5 more

We experimentally studied the switching off processes in the double-resonator coupler superconducting quantum circuit. In both frequency and time-domain, we observed the variation of qubit-qubit effective coupling by tuning the frequency differences between qubits and the double-resonator coupler. According to the measurement results, by just shifting about 50 MHz of qubits' frequencies, we can tune the effective qubit-qubit coupling strength from switching off point to two qubit gate point (effective coupling larger than 5 MHz) in double-resonator superconducting quantum circuit.The double-resonator (coupler) superconducting quantum circuit has the advantage of simple fabrications, introducing less flux noises, reducing occupancy of dilution refrigerator cables,which might supply a promising platform for future large-scale superconducting quantum processors.

M. Podt, Jakob Flokstra, Horst Rogalla

A wide-band double relaxation oscillation superconducting quantum interference device (DROS) with on-chip digital flux locked loop (FLL) circuitry, a Smart DROS, has been realized and experimentally investigated. The key element of the FLL circuitry is a superconducting up–down counter. In order to maximize the flux slew rate, the Smart DROS has been optimized with respect to the coupling between the DROS and the up–down counter, and the quantization unit of the feedback flux. For the Smart DROS with an inductance of 280 pH the flux quantization unit was 5 × 10−2 Φ0. The experiments showed proper operation of the superconducting up–down counter. The full functionality of the complete Smart DROS in a closed loop was demonstrated. For operation at a clock frequency of 100 MHz, a maximum flux slew rate of 5 × 106 Φ0 s−1 was calculated from the measured parameters. Numerical simulations showed that the Smart DROS allows a maximum flux slew rate up to 108 Φ0 s−1 by reducing the area of the Josephson junctions.

Moshe Fibich, Amiram Ron, M. Weger