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| Home > Publications database > Frustrated frustration and strong vortex pinning in Nb-Pt-Nb Josephson junction arrays |
| Home > Publications database > Frustrated frustration and strong vortex pinning in Nb-Pt-Nb Josephson junction arrays |
| Conference Presentation (After Call) | FZJ-2026-01369 |
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2025
Abstract: Josephson junctions are among the most important devices in quantum computing, ranging from superconducting qubits to topological protection through Majorana fermions. They are often studied individually, but arranging them on a one- or two-dimensional grid to form a Josephson array allows to leverage collective phenomena. One proposed application is a topologically protected qubit [1]. When a magnetic field is applied in the out-of-plane direction, quantized circular supercurrents known as Josephson vortices appear. An integer or half-integer number of vortices per unit cell (plaquette) form a rigid lattice. Because vortex movement produces a voltage drop across the leads, the DC resistance dips at (half-)integer values of magnetic flux per unit cell, creating a "frustration pattern". A promising type of Josephson junction for Majorana physics is the multi-terminal Josephson junction, which has more than two superconducting electrodes. We study the frustration pattern of a square lattice with in-situ fabricated Nb-Pt-Nb four-terminal Josephson junctions (4TJJ) and compare it to arrays of conventionally fabricated two-terminal junctions (2TJJ) of different sizes. All arrays reproduce the well-studied frustration behavior. Additionally, the 2TJJ arrays exhibit a strongly pinned state at low temperatures. The magnetoresistance of the array is dominated by the Fraunhofer pattern of the individual junctions. The four-terminal geometry produces a checkerboard pattern of alternating fluxes f and f ′ piercing the plaquettes[2]. This type of frustrated frustration manifests as a beating pattern in the DC resistance. Consequently, 4TJJ arrays enable us to estimate the spatial extent of the central weak-link region. This region must be minimized for topological transitions to occur.[1] Ioffe et al., Nature 415, 503 (2002).[2] Teller et al., Arxiv 2503 14423 (2025)
Keyword(s): Information and Communication (1st) ; Condensed Matter Physics (2nd)
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