Nielsen complexity of coherent spin state operators

Abstract

We calculate Nielsen's circuit complexity of coherent spin state operators. An expression for the complexity is obtained by using the small angle approximation of the Euler angle parametrisation of a general $SO(3)$ rotation. This is then extended to arbitrary times for systems whose time evolutions are generated by couplings to an external field, as well as non-linearly interacting Hamiltonians. In particular, we show how the Nielsen complexity relates to squeezing parameters of the one-axis twisted Hamiltonians in a transverse field, thus indicating its relation with pairwise entanglement. We further point out the difficulty with this approach for the Lipkin-Meshkov-Glick model, and resolve the problem by computing the complexity in the Tait-Bryan parametrisation.

arXiv comment11 Pages

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• Time evolution of spread complexity in quenched Lipkin-Meshkov-Glick model
• Complexity in the Lipkin-Meshkov-Glick Model
• Krylov complexity in quantum many-body scars of spin-1 models
• Time-dependent Hamiltonians and Geometry of Operators Generated by Them
• A formula for the overlap between Generalized Coherent States of any rank one simple Lie algebra