287th RQC Seminar

• 講演者

  Mr. Giovanni Francesco Diotallevi
  ( Institute of Physics, Augsburg University, Germany )

• 日程

  2026年6月24日(水), 13:00 - 14:00(1:00 p.m.-2:00 p.m.)

• 開催場所

  オンサイト（ 224-226 Seminar Room, 2F, Main Research Building, Wako Campus / 和光地区 研究本館2階 特別会議室 (224-226) (C01))

• 講演タイトル

  Effective Hamiltonians and Transport Signatures in Hole-Spin Quantum Devices

• お問合せ

  peter.stano[at]riken.jp

講演概要
Over the past two decades, spin-based approaches have become a central pillar of quantum computing research, with hole spin qubits realized in group-IV semiconductor platforms gaining increasing attention as a particularly viable route forward [1].
These systems combine a number of favorable characteristics, including electric-dipole spin-resonance driving with gate-tunable spin–orbit functionality and gate speeds in the hundreds of megahertz, while recent works on Ge devices have achieved singlequbit fidelities approaching some of the highest values in the field [2]. A crucial aspect behind the adoption of this technology is the development of theoretical and experimental techniques capable of reliably probing the quality of fabricated devices and extracting accurate low-energy descriptions from their underlying microscopic Hamiltonians.
In this seminar, I will present results from two separate projects addressing these goals. First, we revisit the influence of static electric fields on the effective mass of heavy-hole quasiparticles in Ge-based systems [3–5]. Recent studies [6] revealed that conductance measurements in these devices may have been skewed by naive effective-mass estimates for valence-band holes, leading to erroneous assessments of device quality. Motivated by this observation, we explore how the average transport mass [7] in non-parabolic systems may be tuned through specific combinations of charge-carrier density and external electric fields, thereby clarifying the connection between electrostatic confinement, band-structure effects, and experimentally inferred transport properties.
Second, I will discuss a general framework for deriving effective low-energy Hamiltonians using the Schrieffer–Wolff transformation. The Schrieffer–Wolff transformation is a foundational technique in quantum mechanics for perturbatively blockdiagonalizing complex Hamiltonians, isolating the dynamics of interest while systematically rotating away couplings to higherenergy sectors. Despite its widespread use in magnetic systems, superconducting circuits, bosonic modes, and semiconductor qubits, a key limitation lies in the derivation of the transformation generator itself. In infinite-dimensional settings, existing approaches often rely on Hilbert-space truncations or heuristic ans¨atze, obscuring the accuracy, convergence, and range of validity of the resulting effective model.
To bridge this gap, we have developed a fully systematic, closed-form framework for constructing the Schrieffer–Wolff generator without Hilbert-space truncations or heuristic guessing. This approach preserves the full operator structure at every step and yields explicit expressions valid to all orders in perturbation theory [8]. To make these advances accessible, we also developed SymPT [9], an open-source Python package that automates the derivation of Schrieffer–Wolff generators for arbitrary Hamiltonians, static or periodically driven, finite- or infinite-dimensional, single-block or multi-block. Taken together, these results provide both a concrete application to transport and device characterization in Ge hole systems and a general symbolic framework for deriving effective models across a broad class of quantum platforms.