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Measurement Based Quantum Computation ( Mbqc )

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Quantum entanglement, which is often counterintuitive and was originally questioned by Einstein, Podolsky, and Rosen (EPR),1 is now recognized as a versatile resource for quantum information protocols.2,3 In order to meet various requirements for various applications, an important technological development is to increase the number of available entangled qubits. In particular, measurement-based quantum computation (MBQC) requires the cluster type of a large-scale entangled state,4,5 where individual components of the cluster state must be accessible by measuring devices. The number of entangled qubits with individual accessibility seems to be currently limited to a moderate scale.6–8 Shifting to the continuous variable (CV) …show more content…

With the time-domain multiplexing, a cluster state of qumodes can be an arbitrarily long chain in the longitudinal direction by extending the operating time of the cluster-state generator. In spite of the in-principle unlimitation of the time-domain-multiplexing, the previous experimental demonstration of a dual-rail CV cluster state was limited in the number of qumodes,13 due to a technical reason as follows. The optical setup is a large Mach-Zehnder interferometer as depicted in Fig. 1, including a long optical delay line for a shift of qumodes on a rail. The mathematical derivation of the cluster state with this setup is contained in Sec. S1 of the supplementary material. In order to operate this cluster-state generator, the relative phases at all interference points must be properly locked. For this purpose, modulated bright beams are injected into the optical paths of the cluster state as phase probes, and their classical interference signals are exploited as error signals for the feedback control. However, the modulated bright beams are noisy, which obscures objective quantum-level correlation signals of the cluster state. The noises were circumvented in the previous demonstration by chopping the bright beams and by detecting the cluster

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