43 research outputs found
How is a Chordal Graph like a Supersolvable Binary Matroid?
Let G be a finite simple graph. From the pioneering work of R. P. Stanley it
is known that the cycle matroid of G is supersolvable iff G is chordal (rigid):
this is another way to read Dirac's theorem on chordal graphs. Chordal binary
matroids are not in general supersolvable. Nevertheless we prove that, for
every supersolvable binary matroid M, a maximal chain of modular flats of M
canonically determines a chordal graph.Comment: 10 pages, 3 figures, to appear in Discrete Mathematic
Cycle bases for lattices of binary matroids with no Fano dual minor and their one-element extensions
The multivariate Tutte polynomial (alias Potts model) for graphs and matroids
The multivariate Tutte polynomial (known to physicists as the Potts-model partition function) can be defined on an arbitrary finite graph G, or more generally on an arbitrary matroid M, and encodes much important combinatorial information about the graph (indeed, in the matroid case it encodes the full structure of the matroid). It contains as a special case the familiar two-variable Tutte polynomial -- and therefore also its one-variable specializations such as the chromatic polynomial, the flow polynomial and the reliability polynomial -- but is considerably more flexible. I begin by giving an introduction to all these problems, stressing the advantages of working with the multivariate version. I then discuss some questions concerning the complex zeros of the multivariate Tutte polynomial, along with their physical interpretations in statistical mechanics (in connection with the Yang--Lee approach to phase transitions) and electrical circuit theory. Along the way I mention numerous open problems. This survey is intended to be understandable to mathematicians with no prior knowledge of physics
Congruence conditions, parcels, and Tutte polynomials of graphs and matroids
Let be a matrix and be the matroid defined by linear dependence on
the set of column vectors of Roughly speaking, a parcel is a subset of
pairs of functions defined on to an Abelian group satisfying a
coboundary condition (that is a flow over relative to ) and a
congruence condition (that the size of the supports of and satisfy some
congruence condition modulo an integer). We prove several theorems of the form:
a linear combination of sizes of parcels, with coefficients roots of unity,
equals an evaluation of the Tutte polynomial of at a point
on the complex hyperbola $(\lambda - 1)(x-1) = |A|.
On Local Equivalence, Surface Code States and Matroids
Recently, Ji et al disproved the LU-LC conjecture and showed that the local
unitary and local Clifford equivalence classes of the stabilizer states are not
always the same. Despite the fact this settles the LU-LC conjecture, a
sufficient condition for stabilizer states that violate the LU-LC conjecture is
missing. In this paper, we investigate further the properties of stabilizer
states with respect to local equivalence. Our first result shows that there
exist infinitely many stabilizer states which violate the LU-LC conjecture. In
particular, we show that for all numbers of qubits , there exist
distance two stabilizer states which are counterexamples to the LU-LC
conjecture. We prove that for all odd , there exist stabilizer
states with distance greater than two which are LU equivalent but not LC
equivalent. Two important classes of stabilizer states that are of great
interest in quantum computation are the cluster states and stabilizer states of
the surface codes. To date, the status of these states with respect to the
LU-LC conjecture was not studied. We show that, under some minimal
restrictions, both these classes of states preclude any counterexamples. In
this context, we also show that the associated surface codes do not have any
encoded non-Clifford transversal gates. We characterize the CSS surface code
states in terms of a class of minor closed binary matroids. In addition to
making connection with an important open problem in binary matroid theory, this
characterization does in some cases provide an efficient test for CSS states
that are not counterexamples.Comment: LaTeX, 13 pages; Revised introduction, minor changes and corrections
mainly in section V
The circuit and cocircuit lattices of a regular matroid
A matroid abstracts the notions of dependence common to linear algebra, graph theory, and geometry. We show the equivalence of some of the various axiom systems which define a matroid and examine the concepts of matroid minors and duality before moving on to those matroids which can be represented by a matrix over any field, known as regular matroids. Placing an orientation on a regular matroid allows us to define certain lattices (discrete groups) associated to the matroid. These allow us to construct the Jacobian group of a regular matroid analogous to the Jacobian group of a graph. We then survey some recent work characterizing the matroid Jacobian. Finally we extend some results due to Eppstein concerning the Jacobian group of a graph to the case of regular matroids