Rowland Institute at Harvard

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SATO LAB

Rowland Institute at Harvard

Harvard University

While most quantum mechanical effects only appear in matter on the atomic or subatomic scale, superfluids, like superconductors and Bose-Einstein condensates, can exhibit the effects of quantum mechanics acting on the bulk properties of matter on a large scale. When two such quantum systems are weakly coupled together, various fascinating phenomena emerge. In condensed matter systems, superconductors coupled through thin insulators and micro-bridges were the first of this kind to be extensively studied. In our research, we couple two reservoirs of superfluid helium through nanoscale apertures and study their properties governed by quantum mechanics at the macroscopic scale.

Quantum coherence in a superfluid Josephson junction

We report a new kind of experiment in which we take an array of nanoscale apertures that form a superfluid 4He Josephson junction and apply quantum phase gradients directly along the array. We observe collective coherent behaviors from aperture elements, leading to quantum interference. Connections to superconducting and BEC Josephson junctions as well as phase coherence among the superfluid aperture array are discussed.

Physical Review Letters 106, 055302 (2011).

Direct observation of dynamical bifurcation in a superfluid Josephson junction

We report a direct observation of dynamical bifurcation between two plasma oscillation states of a superfluid Josephson junction. We excite the superfluid plasma resonance into a nonlinear regime by driving below the natural plasma frequency and observe a clear transition between two dynamical states. We also demonstrate bifurcation by changing the potential well with temperature variations.

Physical Review Letters 105, 205302 (2010).