Observation of magnetic quantum phase crossovers in a semiconductor spin ladder

Authors:Elizaveta Morozova, Xin Zhang, Utso Bhattacharya, Pablo Cova Fariña, Daniel Jirovec, Alexander Nico-Katz, Stefan D. Oosterhout, Sougato Bose, Giordano Scappucci, Menno Veldhorst, Eugene Demler, Lieven M. K. Vandersypen

Abstract:Understanding collective phases of strongly correlated quantum magnets relies on theoretically tractable model systems with precise microscopic control. Antiferromagnetic spin ladders provide such a setting, hosting field-tunable gapped and gapless phases at half filling and unconventional pairing tendencies upon doping. Here, we realize a programmable Heisenberg spin ladder in a half-filled germanium quantum dot array featuring site-resolved, continuously tunable exchange interactions. Under a fixed magnetic field, we vary the rung and leg coupling to map the rung-singlet, canted antiferromagnetic, and fully polarized phases. Hamiltonian-learning protocols combining equilibrium and dynamical measurements quantitatively characterize the ladder, incorporating spin-orbit interactions to reproduce the observed crossover behavior. Measurements of higher-order spin correlators -- including four-point correlations inaccessible to conventional bulk probes -- reveal signatures of the underlying phase structure despite the finite size. Our results establish germanium quantum dot arrays as a controllable platform for quantum magnetism, opening routes to investigate unconventional superconductivity in doped ladders.

38 pages, 4 figures (main), 12 figures (suppl.)

Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Quantum Physics (quant-ph)

arXiv:2608.17789 [cond-mat.mes-hall]

(or arXiv:2608.17789v1 [cond-mat.mes-hall] for this version)

https://doi.org/10.48550/arXiv.2608.17789 arXiv-issued DOI via DataCite (pending registration)