Hard limits on the postselectability of optical graph states

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

作者机构：Univ Bristol QETLabs HH Wills Phys Lab Merchant Venturers BldgWoodland Rd Bristol BS8 1UB Avon England Univ Bristol Dept Elect & Elect Engn Merchant Venturers BldgWoodland Rd Bristol BS8 1UB Avon England 

出 版 物：《QUANTUM SCIENCE AND TECHNOLOGY》 (Quan. Sci. Tech.)

年 卷 期：2019年第4卷第1期

核心收录：

基　　金：EPSRC [EP/L015730/1, EP/L024020/1] Leverhulme Trust, through Leverhulme Early Career Fellowship [ECF-2018-276] EPSRC [EP/L024020/1, EP/K033085/1] Funding Source: UKRI 

主　　题：entanglement graph states postselection photon sources photonic experiment design linear optical quantum computing numerical methods 

摘      要：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.