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DTSTART:20230101T000000
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DTSTART;TZID=UTC:20240918T153000
DTEND;TZID=UTC:20240918T163000
DTSTAMP:20260611T170733
CREATED:20240915T122521Z
LAST-MODIFIED:20240915T122521Z
UID:7672-1726673400-1726677000@aarms.math.ca
SUMMARY:Atlantic Graph Theory Seminar
DESCRIPTION:Title: How do we use graphs to transmit quantum information? \nTime: 3.30pm\, Atlantic time\, (1:30\, CDT) Wednesday Sept. 18 \nSpeaker: Hermie Monterde\, University of Manitoba \nAbstract: \nIn this talk\, a graph $G$ represents a quantum spin network (a networking of interacting subatomic particles). The vertices and edges of $G$ represent the particles and their interactions in the network. Consider the complex unitary matrix $U(t)=\exp(itA)$\, where $A$ is the adjacency matrix of $G$\, $i^2=-1$ and $t$ is a real number. The propagation of quantum states in the quantum system determined by $G$ is governed by the matrix $U(t)$. In particular\, $|U(t)_{u\,v}|^2$ may be interpreted as the probability that the quantum state assigned at vertex $u$ is transmitted to vertex $v$ at time $t$. In this talk\, we give an overview of the study of quantum state transfer in graphs. We discuss old and new results in this area with emphasis on the concepts and techniques borrowed from graph theory and linear algebra. \n\nZoom link: \nhttps://us02web.zoom.us/j/86861499971?pwd=rTDAaju0TCu24asnaBGvkuNlT11KZ1.1
URL:https://aarms.math.ca/event/atlantic-graph-theory-seminar-15/
LOCATION:Zoom seminar
CATEGORIES:AARMS Atlantic Graph Theory Seminar
ORGANIZER;CN="jeannette Janssen":MAILTO:jeannette.janssen@dal.ca
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=UTC:20240925T150000
DTEND;TZID=UTC:20240925T163000
DTSTAMP:20260611T170733
CREATED:20240925T124502Z
LAST-MODIFIED:20240925T124502Z
UID:7696-1727276400-1727281800@aarms.math.ca
SUMMARY:Atlantic Graph Theory Seminar
DESCRIPTION:Recolouring Graphs: Decompositions\, A Dichotomy Theorem and Frozen   Colourings \nSpeaker: Kathie Cameron\, Wilfrid Laurier University \nA k-colouring of a graph G is an assignment of at most k colours to the vertices of a graph so that the ends of each edge of the graph get different colours. We consider the question: When it is possible to obtain any k-colouring from any other by changing the colour of one vertex at a time\, while always having a k-colouring? This question is equivalent to asking whether the “reconfiguration graph” is connected: The reconfiguration graph of the k-colourings\, denoted Rk(G)\, is the graph whose vertices are the k-colourings of G\, and two colourings are adjacent in Rk(G) if they differ in colour on exactly one vertex. We call a graph recolourable if Rk(G) is connected for every k greater than its chromatic number.\n\nWe have characterized the graphs H such that all graphs G which don’t contain H as an induced subgraph are recolourable. We have done the same when two 4-vertex graphs are excluded as induced subgraphs (except for one class) and for some classes of graphs which exclude as an induced subgraph the path on 5 vertices.\n\nDecompositions are important in solving optimization problems on structured classes of graphs. We have shown that modular decomposition and a stronger version of clique cutsets which we call tight clique cutsets can be used to show that certain classes are recolourable.\n\nA k-colouring of a graph is called frozen if there is no vertex whose colour can be changed so that the result is still a k-colouring. A frozen colouring corresponds to an isolated vertex of the reconfiguration graph\, and thus the existence of a frozen colouring is one way to show that a class of graphs is not recolourable. We have found several new classes of graphs with frozen colourings and an operation which transforms a k-chromatic graph with a frozen (k+1)-colouring into a (k+1)-chromatic graph with a frozen (k+2)-colouring.\nThis is joint work with Manoj Belavadi\, Elias Hildred\, Owen Merkel and Dewi Sintiari.\n\n\nZoom link:\nhttps://us02web.zoom.us/j/86861499971?pwd=rTDAaju0TCu24asnaBGvkuNlT11KZ1.1\n\nMeeting ID: 868 6149 9971\nPasscode: 325258
URL:https://aarms.math.ca/event/atlantic-graph-theory-seminar-16/
LOCATION:Online via Zoom
CATEGORIES:AARMS Atlantic Graph Theory Seminar
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