Macroscopic quantum tunneling and qubit design parameters of Bi 2Sr2CaCu2O8+δ surface intrinsic Josephson junctions

Macroscopic quantum tunneling (MQT) has been demonstrated recently in a Bi2Sr2CaCu2O8+delta surface intrinsic Josephson junction (SIJJ) with its critical current density J(c) below 100 A cm(-2) and its size below 1 mu m. In this work, we present a study of the switching current distributions of SIJJs fabricated on the same crystal, with J(c) > 500 A cm(-2) and size of 0.8 and 1.6 mu m. MQT is clearly observed, and the crossover from MQT to thermal activation (TA) is seen. Our analysis shows that the data agree well with the theoretical predictions of MQT and TA for different-sized SIJJs when parameters that roughly scale with the SIJJ size are used. In the crossover regime, the data are found to be better fitted by considering quantum corrections to TA. We discuss the realistic design of phase- and flux-type qubits using the experimentally attainable SIJJ parameters, which shows that the SIJJs, with their controllable J(c) and size (or junction capacitance), are feasible for qubit applications in the future.