Quantum state systems that count perfect matchings

Abstract

In this paper we show how to categorify the $n$-color vertex polynomial, which is based upon one of Roger Penrose's formulas for counting the number of $3$-edge colorings of a planar trivalent graph. Using topological quantum field theory (TQFT), we introduce a quantum state system to build a new bigraded theory called the bigraded $n$-color vertex homology. The graded Euler characteristic of this homology is the $n$-color vertex polynomial. We then produce a spectral sequence whose $E_\infty$-page is a filtered theory called filtered $n$-color vertex homology and show that it is generated by certain types of face colorings of ribbon graphs. For $n=2$, we show that the filtered $n$-color vertex homology is generated by face colorings that correspond to perfect matchings. Finally, we introduce and give meaning to what the vertex polynomial counts when $n \geq 2$. This polynomial is a new abstract graph invariant that can be inferred from certain formulas of Penrose.