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  • Open Access

Nielsen complexity with multiple cost factors

Marcos Rios Ribeiro1,* and Diego Trancanelli2,†

  • *Contact author: marcosribeiro@usp.br
  • †Contact author: diego.trancanelli@unimore.it
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Phys. Rev. D 114, 085018 – Published 20 October, 2026

DOI: https://doi.org/10.1103/bf4j-b7sm

Abstract

We investigate Nielsen’s geometric approach to quantum complexity in the presence of multiple cost factors, extending the standard framework where a single penalty distinguishes easy from hard directions of the group manifold. By introducing a hierarchy of penalties associated with different degrees of nonlocality, we develop a generalized right-invariant complexity geometry and analyze its implications for geodesic evolution. We derive the modified Euler-Arnold and Jacobi equations and study how multiple cost factors reshape the structure and scaling of conjugate points, where geodesic optimality breaks down. The formalism is illustrated in two settings: a single-qubit system with two cost factors, where we develop a semianalytic approach to investigate complexity growth and its dependence on penalty hierarchies, and Sachdev-Ye-Kitaev-type models, where we analyze both free and chaotic regimes. In these many-body systems, we show that distinct nonlocal sectors generate multiple families of conjugate points whose occurrence depends on both the cost hierarchy and the system size. Our results highlight how refining the penalty structure provides a richer and more realistic description of quantum complexity and its dynamical behavior.

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Phys. Rev. D 114, 085018– Published 20 October, 2026
  • Received 17 June 2026
  • Accepted 7 October 2026
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