Bonn 2025 – scientific programme

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QI: Fachverband Quanteninformation

QI 20: Quantum Networks (joint session QI/Q)

QI 20.7: Talk

Wednesday, March 12, 2025, 16:15–16:30, HS VIII

Collective quantum phases emerging in superconducting qubits networks — •Benedikt J.P. Pernack, Mikhail V. Fistul, and Ilya M. Eremin — Theoretische Physik III, Ruhr-Universität Bochum, Bochum 44801, Germany

We present a theoretical study of collective quantum phases occurring in exemplary vertex-sharing superconducting qubits networks, i.e., frustrated sawtooth chains of Josephson junctions embedded in a dissipationless transmission line. The building block of such networks is a triangular superconducting cell containing two 0-Josephson junctions and one π-Josephson junction. In the frustrated regime, the low-energy quantum dynamics of a single cell is governed by the presence of persistent currents flowing (anti)clockwise corresponding to (anti)vortex configurations. The direct embedding of π-Josephson junctions to the transmission line results in short- or long-range interactions between vortices and antivortices of different cells. Employing a variational approach the quantum dynamics of such qubits networks was mapped to an effective XX spin model where the exchange interaction between spins decays with distance as x^−β, and the local terms represent the coherent quantum superposition of vortex-antivortex pairs [1]. Combining exact numerical diagonalization and quasi-classical mean field approach, we identified various collective quantum phases such as the paramagnetic (P), compressible superfluid (CS) and weakly compressible superfluid (w-CS) states.

[1] B.J.P. Pernack, M.V. Fistul, I.M.Eremin, Phys. Rev. B 110, 184502 (2024).

Keywords: Superconducting qubits network; Interacting spins models; persistent currents; collective quantum phases; commpressible superfluid