Observation of magnetic quantum phase crossovers in a semiconductor spin ladder

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

arXiv · 2608.17789

Observation of magnetic quantum phase crossovers in a semiconductor spin ladder

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

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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.

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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. 2026-08-18. Observation of magnetic quantum phase crossovers in a semiconductor spin ladder. https://arxiv.org/abs/2608.17789

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