Multiterminal Inverse AC Josephson Effect

Abstract

When a Josephson junction is exposed to radio frequency radiation it undergoes the inverse AC Josephson effect -the phase of the junction locks to the drive frequency. As a result, the I − V curves of the junction acquire "Shapiro steps" of quantized voltage. If the junction has three or more superconducting terminals, coupling between different pairs of contacts must be taken into account and the state of the junction evolves in a phase space of higher dimensionality. Here, we study the multi-terminal inverse AC Josephson effect in a graphene sample with four superconducting terminals. We observe correlated switching events caused by the interplay of the connected junctions on the device. Additionally, we find a competition between trivial voltage steps, which are created by the device's resistor network, and nonlinear integer and fractional steps, which are created by the device's Josephson network. We successfully simulate the observed behaviors using a modified 3-dimensional RCSJ model.

Dynamical Stabilization of Multiplet Supercurrents in Multi-terminal Josephson Junctions

“…Numerical simulations involve a fourth-order Runge-Kutta scheme written in tensor form so that the computation of Φ(t) at all bias points can be parallelized over a large number of GPU cores in PyTorch [19,27]. Maps shown in Figure 4 are thus generated in under 20 s [27].…”

“…As the temperature is elevated, the Andreev bound state structure from higher harmonics in the CPR or nondissipative multiple Andreev reflection states should rapidly fade away [39]. However, features that arise due to the larger energy scales of the circuit should be more robust [19].…”

“…We believe, for several reasons, this is an unlikely explanation of the quartet resonances in our device. First, the distance between the contacts is too large to support even two-terminal higher harmonic supercurrents, which require carriers traversing between the contacts multiple times [19]. Indeed, multiplet resonances are robust to elevated temperatures (see [27]).…”

“…When a third superconducting contact is added, the washboard potential becomes two-dimensional, which expands the complexity of the phase trajectories [19]. When a bias is applied to one of the contacts, it causes movement along the associated phase axis.…”

Selective Control of Conductance Modes in Multi-terminal Josephson Junctions

“…MTJJs may also find application as circuit elements for coupling multiple qubits [14,[25][26][27]. Additionally, they have shown rich transport features such as the coexistence of superconducting and dissipative currents [28], fractional Shapiro steps [29], generalizations of multiple Andreev reflections (MAR) [30,31], multi-loop superconducting interferometry [32,33] and exotic Cooper quartet transport [34,35].…”