Spectral description of non-commutative local systems on surfaces and non-commutative cluster varieties

Let R be a non-commutative field. We prove that generic triples of flags in an m-dimensional R-vector space are described by flat R-line bundles on the honeycomb graph with (m-1)(m-2)/2 holes. Generalising this, we prove that the non-commutative moduli space X(m,S) of (twisted) framed flat R-vector bundles of rank m on a decorated surface S is birationally identified with the moduli spaces of (twisted) flat line bundles on a spectral surface $Sigma_Gamma$ assigned to certain bipartite graphs $Gamma$ on S. We introduce non-commutative cluster Poisson varieties related to bipartite ribbon graphs. They carry a canonical non-commutative Poisson structure. The result above just means that the space X(m, S) has a structure of a non-commutative cluster Poisson variety, equivariant under the action of the mapping class group of S. For bipartite graphs on a torus, we get the non-commutative dimer cluster integrable system. We develop a parallel dual story of non-commutative cluster A-varieties related to bipartite ribbon graphs. They carry a canonical non-commutative 2-form. The dual non-commutative moduli space A(m,S) of twisted decorated local systems on S carries a cluster A-variety structure, equivariant under the action of the mapping class group of S. The non-commutative cluster A-coordinates on the space A(m,S) are expressed as ratios of Gelfand-Retakh quasideterminants. In the case m=2 this recovers the Berenstein-Retakh non-commutative cluster algebras related to surfaces. We introduce stacks of admissible dg-sheaves on surfaces, and use them to give an alternative microlocal proof of the above results.