iSWAP maximises the second-moment spectral gap in random quantum circuits

We prove that the $\mathrm{iSWAP}$ gate maximises the spectral gap of the Hermitian second-moment operator on every connected graph with at least three vertices, among all two-local unitary circuit ensembles. We further prove that the polyhedral cone defined by asymmetric four-point inequalities is invariant under the transpose of the $\mathrm{iSWAP}$ semigroup, yielding a componentwise comparison certificate for its positive Perron--Frobenius eigenvector. These results resolve a conjecture of Kong, Li, and Liu.

Source: arXiv:2607.29551v1 - http://arxiv.org/abs/2607.29551v1 PDF: https://arxiv.org/pdf/2607.29551v1 Original Link: http://arxiv.org/abs/2607.29551v1