Single-Crystal Josephson Junctions for Experiments in Quantum Computation

Rosario Fazio, Yuriy Makhlin, Gerd Schön

H. B. Wang, Yuta Aruga, J. Chen +3 more

With a thin gold layer, we fabricated mesa-like shunted intrinsic Josephson junction stacks on Bi2Sr2CaCu2O8+x single crystals. Instead of the multibranch structure and large voltage jumps often observed in conventional intrinsic junctions, current–voltage characteristics typical of resistively shunted junctions were obtained. Individual Shapiro steps were clearly visible with irradiation at frequencies from a few to 20 GHz. The experiments demonstrated not only the ac Josephson effects directly but also the possibility of employing intrinsic Josephson junctions in high-frequency applications.

Federico Paolucci, Francesco Vischi, Giorgio De Simoni +3 more

Gate-tunable Josephson junctions (JJs) are the backbone of superconducting classical and quantum computation. Typically, these systems exploit low-charge-concentration materials and present technological difficulties limiting their scalability. Surprisingly, electric field modulation of a supercurrent in metallic wires and JJs has been recently demonstrated. Here, we report the realization of titanium-based monolithic interferometers which allow tuning both JJs independently via voltage bias applied to capacitively coupled electrodes. Our experiments demonstrate full control of the amplitude of the switching current ( I s ) and of the superconducting phase across the single JJ in a wide range of temperatures. Astoundingly, by gate-biasing a single junction, the maximum achievable total I s is suppressed down to values much lower than the critical current of a single JJ. A theoretical model including gate-induced phase fluctuations on a single junction accounts for our experimental findings. This class of quantum interferometers could represent a breakthrough for several applications such as digital electronics, quantum computing, sensitive magnetometry, and single-photon detection.

K. Ch. Chatzisavvas, C. Daskaloyannis, C. P. Panos

Gerd Hechtfischer, W. Walkenhorst, Gerhard Kunkel +4 more

We report on high frequency experiments with mesa structures patterned on Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+y/ single crystals (BSCCO). Due to the intrinsic Josephson effect between adjacent CuO/sub 2/ bilayers these mesas form stacks of 100 to 500 Josephson junctions. The ac-Josephson effect was investigated in the frequency range between 6 GHz and 120 GHz. We focus our interest on possible applications of intrinsic Josephson junctions as flux-flow oscillators and high-frequency mixers. These components form the essential parts of an integrated mm-wave receiver in BSCCO technology.

Serhii E. Shafranjuk, John B. Ketterson