Hard limits on the postselectability of optical graph states

Jeremy C. Adcock, Sam Morley-Short, Joshua W. Silverstone, Mark G. Thompson

Research output: Contribution to journalArticle (Academic Journal)peer-review

17 Citations (Scopus)
164 Downloads (Pure)


Coherent control of large entangled graph states enables a wide variety of quantum information processing tasks, including error-corrected quantum computation. The linear optical approach offers excellent control and coherence, but today most photon sources and entangling gates—required for the construction of large graph states—are probabilistic and rely on postselection. In this work, we provide proofs and heuristics to aid experimental design using postselection. We introduce a versatile design rule for postselectable experiments: drawn as a graph, with qubit as vertices and gates and photon-pair sources as edges, an experiment may only contain cycles with an odd number of sources. We analyse experiments that use photons from postselected photon-pair sources, and lower bound the number of accessible classes of graph state entanglement in the non-degenerate case—graph state entanglement classes that contain a tree are are always accessible. The proportion of graph states accessible by postselection shrinks rapidly, however. We list accessible classes for various resource states up to 9 qubits. Finally, we apply these methods to near-term multi-photon experiments.
Original languageEnglish
Article number015010
Number of pages20
JournalQuantum Science and Technology
Issue number1
Early online date28 Nov 2018
Publication statusPublished - 1 Jan 2019

Structured keywords

  • QETLabs
  • Photonics and Quantum


  • entanglement
  • graph states
  • linear optical quantum computing
  • numerical methods
  • photon sources
  • photonic experiment design
  • postselection


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