Quantum Dynamics of LC shunted Nb/Al-AlO$_x$/Nb Josephson Junctions

H. Kohlstedt, Alexey Vladimirovich Ustinov, Matteo Cirillo +1 more

Lucia Capogna, Giovanni Costabile, Paola Barbara +2 more

Norimichi Watanabe, Susumu Abe, Akiyoshi Nakayama

Ch. Kaiser, Thilo Bauch, Floriana Lombardi +1 more

We have studied both theoretically and experimentally how an LC series circuit connected in parallel to a Josephson junction influences the Josephson dynamics. The presence of the shell circuit introduces two energy scales, which in specific cases, can strongly differ from the plasma frequency of the isolated junction. Josephson junctions were manufactured using the Nb/Al-AlOx/Nb fabrication technology with various on-chip LC shunt circuits. Spectroscopic measurements in the quantum limit show excellent agreement with theory taking into account the shunt inductance and capacitance in the resistively and capacitively shunted junction model. The results clearly show that the dynamics of the system are two-dimensional, resulting in two resonant modes of the system. These findings have important implications for the design and operation of Josephson junction based quantum bits.

V. K. Kaplunenko, M. Khabipov, E. Goldobin

The authors propose a new type of sampler design based on shunted junctions ( beta c =1). The sampler is to be used for the investigation of single flux quantum devices (RSFQ) employing similar junctions (Kaplunenko et al. 1989, Filippenko et al. 1991). They measure the time resolution of the sampler and delay time of the shunted Josephson junction array. The circuit was manufactured on a single chip and was DC powered. They employed Nb-AlO x -Nb tunnel junctions of 300 A m -2 critical current density and observed Josephson oscillations of the output junction at frequencies from 6 to 50 GHz. Despite a long plasma period of 20 ps the time resolution was 5 ps. The transmission line of 27 Josephson junctions (critical current 165 mu A each) demonstrated time delay of 0.5 ps mu A -1 .

Perng-Fei Yuh, E.E. Stebbins

We report the development of a 256-stage, one-bit superconducting digital correlator functionally tested at a highest clock frequency of 10.232 GHz and data rate of 1.279 Gb/s. The correlator consists of two 256-bit shift registers for delay and storage, 256 exclusive-OR gates for multiplication, and 256 shunted SQUID's to produce an analog summing output. It is fabricated using a Nb/AlO/sub x//Nb Josephson-junction process at a critical-current density of 1000 A/cm/sup 2/. The 5-mm square chip uses about 4350 Nb/AlO/sub x//Nb Josephson junctions and consumes about 0.4 mW.>