Coherent-cluster-state generation in networks of degenerate optical parametric oscillators

TL;DR

This paper demonstrates the theoretical possibility of generating coherent cluster states in networks of degenerate optical parametric oscillators, with numerical analysis of realistic conditions and methods to improve state quality.

Contribution

It introduces a method to generate coherent cluster states in DOPO networks using beam splitters and classical pumps, expanding quantum resource options for quantum computing.

Findings

Coherent cluster states can be generated in DOPO networks under ideal conditions.

Numerical analysis identifies minimum requirements for realistic generation.

Nonequilibrium pumps can enhance the quality of generated cluster states.

Abstract

Cluster states are versatile quantum resources and an essential building block for measurement-based quantum computing. The possibility to generate cluster states in specific systems may thus serve as an indicator regarding if and to what extent these systems can be harnessed for quantum technologies and quantum information processing in particular. Here, we apply this analysis to networks of degenerate optical parametric oscillators (DOPOs), also called coherent Ising machines (CIMs). CIMs are distinguished by their highly flexible coupling capabilities, which makes it possible to use them, e.g., to emulate large spin systems. As CIMs typically operate with coherent states (and superpositions thereof), it is natural to consider cluster states formed by superpositions of coherent states, i.e., coherent cluster states. As we show, such coherent cluster states can, under ideal conditions, be generated in DOPO networks with the help of beam splitters and classical pumps. Our subsequent numerical analysis provides the minimum requirements for the generation of coherent cluster states under realistic conditions. Moreover, we discuss how nonequilibrium pumps can improve the generation of coherent cluster states. In order to assess the quality of the cluster-state generation, we map the generated states to an effective spin space using modular variables, which allows us to apply entanglement criteria tailored for spin-based cluster states.