136 research outputs found
Loss and decoherence at the quantum Hall - superconductor interface
High quality type-II superconducting contacts have recently been developed to
a variety of 2D systems, allowing one to explore the superconducting proximity
in the quantum Hall (QH) regime. Inducing superconducting correlations into a
chiral system has long been viewed as a route for creating exotic topological
states and excitations. However, it appears that before these exciting
predictions could be realized, one should develop a better understanding of the
limitations imposed by the physics of real materials. Here, we perform a
systematic study of Andreev conversion at the interface between a
superconductor and graphene in the QH regime. We find that the probability of
Andreev conversion of electrons to holes follows an unexpected but clear trend:
the dependencies on temperature and magnetic field are nearly decoupled. We
discuss these trends and the role of the superconducting vortices, whose normal
cores could both absorb and dephase the individual electrons in a QH edge. Our
study may pave the road to engineering future generation of hybrid devices for
exploiting superconductivity proximity in chiral channels
Dynamical Stabilization of Multiplet Supercurrents in Multi-terminal Josephson Junctions
The dynamical properties of multi-terminal Josephson junctions have recently
attracted interest, driven by the promise of new insights into synthetic
topological phases of matter and Floquet states. This effort has culminated in
the discovery of Cooper multiplets, in which the splitting of a Cooper pair is
enabled via a series of Andreev reflections that entangle four (or more)
electrons. In this text, we show conclusively that multiplet resonances can
also emerge as a consequence of the three terminal circuit model. The
supercurrent appears due to the correlated phase dynamics at values that
correspond to the multiplet condition of applied bias. The
emergence of multiplet resonances is seen in i) a nanofabricated three-terminal
graphene Josephson junction, ii) an analog three terminal Josephson junction
circuit, and iii) a circuit simulation. The mechanism which stabilizes the
state of the system under those conditions is purely dynamical, and a close
analog to Kapitza's inverted pendulum problem. We describe parameter
considerations that best optimize the detection of the multiplet lines both for
design of future devices. Further, these supercurrents have a classically
robust energy contribution, which can be used to engineer qubits
based on higher harmonics
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