Efficient detection of useful long-range entanglement in imperfect cluster states

Abstract

Photonic cluster states are a crucial resource for optical quantum computing. Recently a quantum dot single photon source has been demonstrated to produce strings of photons in a linear cluster state, but high photon loss rates make it impossible to characterize the entanglement generated by conventional methods. We present a benchmarking method for such sources that can be used to demonstrate useful long-range entanglement with currently available collection/detection efficiencies below 1%. Measurement of the polarization state of single photons in different bases can provide an estimate for the three-qubit correlation function <ZXZ>. This value constrains correlations spanning more than three qubits, which in turn provide a lower bound for the localizable entanglement between any two qubits in the large state produced by the source. Finite localizable entanglement can be established by demonstrating <ZXZ> > 2/3. This result enables photonic experiments demonstrating computationally useful entanglement with currently available technology.

arXiv comment8 pages, 4 figures, 20 references

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Cited by in corpus (4)

• Photonic tensor networks produced by a single quantum emitter
• Independent high-purity photons created in domain-engineered crystals
• Time-bin entanglement in the deterministic generation of linear photonic cluster states
• Efficient tomography of microwave photonic cluster states