Four-body interactions in Kerr parametric oscillator circuits

TL;DR

This paper introduces new Kerr parametric oscillator circuits with four-body interactions, simplifying fabrication and enabling scalable quantum annealing for Ising spin embedding using the LHZ scheme.

Contribution

It proposes a novel circuit design with linear couplers for four-body interactions and experimentally demonstrates four-body correlations in a four-KPO system.

Findings

Four-body interactions successfully implemented and measured.

Coupling constants comparable to conventional nonlinear circuits.

Quantum annealing demonstrated using the LHZ scheme.

Abstract

We theoretically present new unit circuits of Kerr parametric oscillators (KPOs) with four-body interactions, which enable the scalable embedding of all-to-all connected logical Ising spins using the Lechner-Hauke-Zoller (LHZ) scheme. These unit circuits enable four-body interactions using linear couplers, making the circuit fabrication and characterization much simpler than those of conventional unit circuits with nonlinear couplers. Numerical calculations indicate that the magnitudes of the coupling constants can be comparable to those in conventional circuits. On the basis of this theory, we designed a four-KPO circuit and experimentally confirmed the four-body correlation by measuring the pump-phase dependence of the parity of the four-KPO states. We show that the choice of the pump frequencies are important not only to enable the four-body interaction, but to cancel the effects of other unwanted interactions. Using the circuit, we demonstrated the quantum annealing based on the LHZ scheme, where the strength of the interaction between the logical Ising spins is mapped to the local field and controlled by a coherent drive applied to each KPO.