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Given a sequence of real symmetric $(2^N\times 2^N)$- matrices $(H_N)_{N\in\mathbb{N}}$ on the $N$-fold tensor product of $\mathbb{C}^2$ with itself, such that \begin{align} \lim_{N\to\infty}||[H_N,S_N]||_N=0, \end{align} where $||\cdot||_N$ denotes the operator norm on $B(\bigotimes_{n=1}^N\mathbb{C}^2)$ (the space of bounded liner operators on $\bigotimes_{n=1}^N\mathbb{C}^2$), $[\cdot,\cdot]$ the usual commutator, and the matrix $S_N$ denotes the symmetrization (projection) operator given by linear extension of the following map on elementary tensors: \begin{align}S_N (v_1 \otimes \cdots \otimes v_N) = \frac{1}{N!} \sum_{\sigma \in {\cal P}(N)} v_{\sigma(1)} \otimes \cdots \otimes v_{\sigma(N)}, \end{align} where ${\cal P}(N)$ denotes the symmetric group. It is known that for all $N\in\mathbb{N}$ the ground state eigenvector $\psi_N$ of $H_N$ (i.e. the eigenvector corresponding to two lowest eigenvalue of $H_N$) is unique and has strictly positive components. My question is if we can conclude that \begin{align} \lim_{N\to\infty}||S_N\psi_N-\psi_N||_N=0, \end{align} where the latter norm is considered on the space $\bigotimes_{n=1}^N\mathbb{C}^2$.

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  • $\begingroup$ Some of your terminology is more physics-y and less math-y than I am used to. When you talk of the ground state eigenvector of $H_N$, what is the associated eigenvalue? $\endgroup$
    – Yemon Choi
    Commented Dec 20, 2019 at 14:05
  • $\begingroup$ I mean the eigenvector related to the lowest eigenvalue. So the ground state eigenvector corresponds to the lowest eigenvalue of H_N. $\endgroup$
    – Kris
    Commented Dec 20, 2019 at 14:17
  • $\begingroup$ OK, but what are we allowed to assume about this eigenvalue? Is it strictly positive, for instance? $\endgroup$
    – Yemon Choi
    Commented Dec 20, 2019 at 14:44
  • $\begingroup$ Good point, we know that this lowest eigenvalue equals: -(largest eigenvalue). Moreover, we know that it is unique, so that the corresponding eigenspace is one-dimensional. $\endgroup$
    – Kris
    Commented Dec 20, 2019 at 14:52

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