Spectra of Gauge Code Hamiltonians

Abstract

We study the spectral gap of frustrated spin (qubit) Hamiltonians constructed from quantum subsystem (gauge) codes. Such a Hamiltonian can be block diagonalized, with blocks labelled by eigenvalues of extensively many integrals of motion (stabilizers of the code.) Of particular interest is the 3D gauge color code, whose Hamiltonian has been conjectured to act as a quantum memory at finite temperature. Using Perron-Frobenius theory we constrain the location of first and second eigenvalues among the blocks of the Hamiltonian. This allows us to numerically find the gap of some large instances of the 3D gauge color code, which is compared to other frustrated spin Hamiltonians. Finally, we suggest a relation between bounded stabilizers and gapped spectra.