Quantum approaches to graph colouring

CARLA VANESSA DA SILVA, Ana Aguiar, Priscila M. V. Lima +1 more

Chris D. Godsil, Newman, M. W.

We deal with a graph colouring problem that arises in quantum information theory. Alice and Bob are each given a $\pm1$-vector of length $k$, and are to respond with $k$ bits. Their responses must be equal if they are given equal inputs, and distinct if they are given orthogonal inputs; however, they are not allowed to communicate any information about their inputs. They can always succeed using quantum entanglement, but their ability to succeed using only classical physics is equivalent to a graph colouring problem. We resolve the graph colouring problem, thus determining that they can succeed without entanglement exactly when $k\leq3$.

Halima Djelloul, Abdesslem Layeb, Salim Chıkhı

The graph colouring problem (GCP) is one of the most interesting, studied and difficult combinatorial optimisation problems. That is why, several approaches were developed for solving this problem, including exact approaches, heuristic approaches, metaheuristics and hybrid approaches. In this paper, we try to solve the graph colouring problem using a new approach based on the quantum inspired cuckoo search algorithm. The first contribution consists in defining an appropriate quantum representation based on qubit representation to represent the graph colouring solutions. The second contribution is the proposition of a novel measure operator based on the adjacency matrix. The third contribution involves the proposition of an adapted hybrid quantum mutation operation. To show the feasibility and the effectiveness of the algorithm, we have used the standard DIMACS benchmark, and the obtained results are very encouraging.

Olawale Titiloye, Alan J. Crispin

Michael Epping, Tobias Stollenwerk

We present a novel algorithmic approach to find a proper vertex colouring of a graph with d colours, if it exists. We associate a d-dimensional quantum system with each vertex and the initial state is a mixture of all possible colourings, from which we obtain a random proper colouring of the graph by measurements. The non-deterministic nature of the quantum measurement is tackled by a reset operation, which can revert the effect of unwanted projections. As in the classical case, we find that the runtime scales exponentially with the number of vertices. However, we provide numerical evidence that the average runtime for random graphs scales polynomially in the number of edges.