Implementation of a quantum cubic gate by adaptive non-Gaussian measurement

TL;DR

This paper proposes a practical scheme for implementing a quantum cubic gate using adaptive non-Gaussian measurement, highlighting the role of classical control and non-Gaussian ancillas in achieving nonlinearity and noise suppression.

Contribution

It introduces a novel non-Gaussian measurement scheme and a simple implementation method for the quantum cubic gate on traveling light beams.

Findings

Nonlinearity is generated by classical adaptive control, independent of nonclassicality.

Non-Gaussian ancilla suppresses excess noise in the output.

Performance depends on the choice of non-Gaussian ancilla within current technological capabilities.

Abstract

We present a concept of non-Gaussian measurement composed of a non-Gaussian ancillary state, linear optics and adaptive heterodyne measurement, and on the basis of this we also propose a simple scheme of implementing a quantum cubic gate on a traveling light beam. In analysis of the cubic gate in the Heisenberg representation, we find that nonlinearity of the gate is independent from nonclassicality; the nonlinearity is generated solely by a classical nonlinear adaptive control in a measurement-and-feedforward process while the nonclassicality is attached by the non-Gaussian ancilla that suppresses excess noise in the output. By exploiting the noise term as a figure of merit, we consider the optimum non-Gaussian ancilla that can be prepared within reach of current technologies and discuss performance of the gate. It is a crucial step towards experimental implementation of the quantum cubic gate.