Macroscopic Quantum Tunneling Phenomena In Bi-2212 Surface Intrinsic Josephson Junctions

Electrons in superconductors can form Cooper pairs and condense into the ground state,which can be described by a macroscopic quantum wave function. The phase of the wave function is an important parameter in reflecting the collective movement of millions of Cooper pairs. Superconducting Josephson junction devices are excellent systems for demonstrating macroscopic quantum phenomena.Macroscopic quantum phenomena in Josephson junction devices have been studied for more than 20 years. One of the aims is to study the laws of quantum mechanics applicable to the macroscopic system. A number of experimental results have shown that macroscopic quantum phenomena are observable in the macroscopic or mesoscopic Josephson junction systems. Superconducting quantum system, which is based on the Josephson junctions, is a macroscopic quantum object. At extreme low temperatures, it can display macroscopic quantum phenomena. This system has good quantum coherence, and its quantum properties can be easily controlled by the field and circuit parameters. In the Josephson devices, various interesting macroscopic quantum phenomena, such as macroscopic quantum tunneling, the quantum energy levels and quantum coherence effects, the superposition of quantum states, as well as Rabi oscillations have been demonstrated.Under the extreme low-temperature condition, the current-biased Josephson junctions can be considered as one of the simplest superconducting macroscopic quantum systems, which can be described as a phase particle with certain mass and damping moving in a washboard potential. In this work, we successfully used photolithographic and electron-beam lithographic techniques to fabricate surface intrinsic Josephson junctions (SIJJs) on the high-Tc Bi₂Sr₂CaCu₂O_8+δsingle crystals. We achieved mK temperature level in an Oxford Kelvinox MX400 dilution refrigerator.Based upon these, the switching current distributions of Bi₂Sr₂CaCu₂O_8+δ SIJJs were measured in the temperature range of 25 mK to 1 K. We found that the experimental results can be well fitted by considering macroscopic quantum tunneling (MQT) in the low temperature regime and by thermally activated process in the high temperature regime. However, the fitting is unsatisfactory at the intermediate temperatures. To improve the fitting, corrections due to quantum fluctuations are considered. It is found that quantum corrections lead to a perfect fit to the experimental data. These results are useful for the further studies of MQT in SIJJs and for their possible applications as superconducting qubits.