Optically Induced Josephson Effect

Felix Cheung

Clark A. Hamilton

C. Vanneste, Alain Gilabert, P. Sibillot +1 more

We report experimental measurement of the dynamic response of optically induced superconducting weak links modulated at up to 1 GHz. Increasing the optical modulation depth from 7 to 70% as the frequency varies from low frequency to 30 MHz extinguishes the ac Josephson effect which is consistent with a calculated thermal response time of 150×10−9 sec.

Fumi Irie, Ai Nakamura

Annesh Mukhopadhyay, Xi-Wang Luo, Colby E. Schimelfenig +4 more

The momentum space Josephson effect describes the supercurrent flow between weakly coupled Bose-Einstein condensates (BECs) at two discrete momentum states. Here, we experimentally observe this exotic phenomenon using a BEC with Raman-induced spin-orbit coupling, where the tunneling between two local band minima is implemented by the momentum kick of an additional optical lattice. A sudden quench of the Raman detuning induces coherent spin-momentum oscillations of the BEC, which is analogous to the ac Josephson effect. We observe both plasma and regular Josephson oscillations in different parameter regimes. The experimental results agree well with the theoretical model and numerical simulation and showcase the important role of nonlinear interactions. We also show that the measurement of the Josephson plasma frequency gives the Bogoliubov zero quasimomentum gap, which determines the mass of the corresponding pseudo-Goldstone mode, a long-sought phenomenon in particle physics. The observation of momentum space Josephson physics offers an exciting platform for quantum simulation and sensing utilizing momentum states as a synthetic degree.

Takashi Noguchi, K. Ohsawa, Seizo Morita +1 more

The ac Josephson effects in Nb point contacts were measured using optically pumped sub-millimeter-wave laser. Laser-induced constant voltage steps (Shapiro steps) were observed on the dc I–V curves of the hysteretic junction as well as non-hysteretic junctions. We found that the height of the fundamental step normalized to the critical current at no irradiation in hysteretic junctions was considerably larger than that previously reported. The enhancement of the step observed can be explained by taking the effect of the shunt capacitance into consideration.