Novel macroscopic quantum effects due to interactions between intrinsic Josephson junctions

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Intrinsic Josephson junction(IJJ) systems, where the superconducting layer and the insulating layer are stacked in an atomic scale, is extensively attracted as a possible candidate of future quantum information processing technology. In this study, we investigate the interlayer coupling effects, which are essentially important for the IJJ systems, to fundamental phenomena of quantum bits operation, such as anenergy level quantization(ELQ) in macroscopic quantum tunneling(MQT) state. We observed that the separation of the switching current probability distribution attributed to ELQ under microwave irradiation is variedwith increasing temperatures. We also found that a crossover temperature to MQT regime is strongly dependent on the junction geometry of IJJs. Finally, we succeeded in fabricating an IJJ device with small junction numbers below 10 junctions, which is quite useful for the understanding of the interlayer coupling effects.