Digital Quantum Simulation of Spin Models with Circuit Quantum Electrodynamics

Systems of interacting quantum spins show a rich spectrum of quantum phases and display interesting many-body dynamics. Computing characteristics of even small systems on conventional computers poses significant challenges. A quantum simulator has the potential to outperform standard computers in calculating the evolution of complex quantum systems. Here, we perform a digital quantum simulation of the paradigmatic Heisenberg and Ising interacting spin models using a two transmon-qubit circuit quantum electrodynamics setup. We make use of the exchange interaction naturally present in the simulator to construct a digital decomposition of the model-specific evolution and extract its full dynamics. This approach is universal and efficient, employing only resources that are polynomial in the number of spins, and indicates a path towards the controlled simulation of general spin dynamics in superconducting qubit platforms.

Double proximity effect in lateral S-NF-S junctions

We investigate planar Josephson junctions where the intermediate spacer between the two superconductors is an hybrid structure made by a normal metal and a ferromagnet. The different behaviors of the S-N-S junctions with thicknesses of 50 nm in both Cu and Nb layers, and S-N/F-S junctions with 10 nm of Co, 50 nm of Cu and 50 nm of Nb are studied. In this way, we analyze the influence of the ferromagnetic exchange interaction on the proximity effect. A dramatic supression of the josephson critical current of the Nb-(Cu/Co)-Nb junctions is observed. We believe that the reason for this is due to the length scale of the superconducting correlations of the electrons and holes of the weak link is larger than the thickness of Cu/Co bilayer.