English

Bounding the Frobenius norm of a q-deformed commutator

Quantum Algebra 2022-03-21 v2 Mathematical Physics math.MP

Abstract

For two n×nn \times n complex matrices AA and BB, we define the qq-deformed commutator as [A,B]q:=ABqBA[ A, B ]_q := A B - q BA for a real parameter qq. In this paper, we investigate a generalization of the B\"{o}ttcher-Wenzel inequality which gives the sharp upper bound of the (Frobenius) norm of the commutator. In our generalisation, we investigate sharp upper bounds on the qq-deformed commutator. This generalization can be studied in two different scenarios: firstly bounds for general matrices, and secondly for traceless matrices. For both scenarios, partial answers and conjectures are given for positive and negative qq. In particular, denoting the Frobenius norm by .F||.||_F, when either AA or BB is normal, we prove the following inequality to be true and sharp: [A,B]qF2(1+q2)AF2BF2|| [ A , B ]_q||_F^2 \le \left(1+q^2 \right) ||A||_F^2 ||B||_F^2 for positive qq. Also, we conjecture that the same bound is true for positive qq when either AA or BB is traceless. For negative qq, we conjecture other sharp upper bounds to be true for the generic scenarios and the scenario when either of AA or BB is traceless. All conjectures are supported with numerics and proved for n=2n=2.

Keywords

Cite

@article{arxiv.2202.11520,
  title  = {Bounding the Frobenius norm of a q-deformed commutator},
  author = {Dariusz Chruściński and Gen Kimura and Hiromichi Ohno and Tanmay Singal},
  journal= {arXiv preprint arXiv:2202.11520},
  year   = {2022}
}

Comments

A shortcoming in the earlier proof of Proposition 1 has been remedied. A new and more elementary proof is provided for Proposition 3; the older proof is also retained. 18 pages and 4 figures. All comments are welcome