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Perturbative power series for block diagonalisation of Hermitian matrices

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arxiv 2408.14637 v1 pith:ZBNPGCVD submitted 2024-08-26 quant-ph

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keywords blockdiagonalisationactionconditionshermitianleastmatricesperturbative
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Block diagonalisation of matrices by canonical transformation is important in various fields of physics. Such diagonalization is currently of interest in condensed matter physics, for modelling of gates in superconducting circuits and for studying isolated quantum many-body systems. While the block diagonalisation of a particular Hermitian matrix is not unique, it can be made unique with certain auxiliary conditions. It has been assumed in some recent literature that two of these conditions, ``least action" vs. block-off-diagonality of the generator, lead to identical transformations. We show that this is not the case, and that these two approaches diverge at third order in the small parameter. We derive the perturbative power series of the ``least action", exhibiting explicitly the loss of block-off-diagnoality.

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Cited by 2 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Closed-Form Generators for Perturbative Transformations in Static and Periodically Driven Quantum Systems

    quant-ph 2024-11 conditional novelty 6.0 of 10

    A closed-form, truncation-free expression for the Schrieffer-Wolff generator is derived for finite-plus-bosonic quantum systems, with a Fourier-space extension for periodic drives.

  2. SymPT: a comprehensive tool for automating effective Hamiltonian derivations

    quant-ph 2024-12 conditional novelty 5.0 of 10

    SymPT automatically derives effective Hamiltonians via Schrieffer-Wolff transformations and extensions for time-independent and time-periodic quantum systems, without truncating the Hilbert space.

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