Discrepancy between Chimera Graphs

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  Sukhraan S  (Report)

  November 30, 2020 17:41

  Hi Thomas,

  Thank you for your question. There seems to be some confusion, which our team would be happy to clarify.

  The chimera_graph(m,n) function in the dwave_networkx package is used to generate a chimera lattice of m number of rows and n number of columns (https://docs.ocean.dwavesys.com/projects/dwave-networkx/en/latest/reference/generated/dwave_networkx.chimera_graph.html) with each block being a chimera unit cell.

   

  The following is a code example that shows how to plot a single unit cell in a chimera lattice:

  

  The graph plotted above represents a singular chimera unit cell with the nodes representing qubits and the edges representing couplers. Each of the 4 horizontal qubits connects to each of the 4 vertical qubits via internal couplers, forming a K4,4 graph (as seen in the picture above).

   

  The chimera topology in the D-Wave DW2000Q QPU chip supports a 16x16 chimera lattice(referred by C16 notation) which consists of 16 rows * 16 columns  of those unit cells of 8 qubits and this is what you would see in the documentation present here (https://docs.dwavesys.com/docs/latest/c_gs_4.html).

  

  

  (The pictures above shows how the Chimera unit cells can be represented in column or crossed representation, with the latter being the same as the one produced by the chimera_graph(m,n) function)

  On the fabricated chip, unit cells are laid out as below, with each chimera unit cell connected by external couplers (represented by connected blue circles, which connect adjacent unit cells):

  

  (The picture above shows three 8 qubit unit cells, connected horizontally via external couplers)

  Additional Resources: https://support.dwavesys.com/hc/en-us/articles/360003695354-What-is-the-Chimera-Topology-

  I hope this clarifies your question. If you have any further concerns, please feel free to reach out again on our community thread.

   

   

   

   

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  Thomas D  (Report)

  December 01, 2020 08:50

  Thank you a lot, now it's much clearer.

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