Nonlinear squeezing for measurement-based non-Gaussian operations in time domain

TL;DR

This paper demonstrates the generation and real-time measurement of nonlinear squeezing in non-Gaussian states, advancing measurement-based quantum operations in continuous-variable optical systems.

Contribution

It experimentally verifies nonlinear squeezing in superpositions of vacuum and single photon states, crucial for implementing non-Gaussian gates in quantum computing.

Findings

Nonlinear squeezing observed via real-time quadrature measurements.

Generated states are compatible with real-time feedforward.

Potential for further improvement with higher photon number states.

Abstract

Quantum non-Gaussian gate is a missing piece to the realization of continuous-variable universal quantum operations in the optical system. In a measurement-based implementation of the cubic phase gate, a lowest-order non-Gaussian gate, non-Gaussian ancillary states that has a property we call nonlinear squeezing are required. This property, however, has never been experimentally verified. In this paper, we generate a superposition between a vacuum state and a single photon state whose nonlinear squeezing are maximized by the optimization of the superposition coefficients. The nonlinear squeezing is observed via real-time quadrature measurements, meaning that the generated states are compatible with the real-time feedforward and are suitable as the ancillary states for the cubic phase gate in time domain. Moreover, by increasing the number of the photons, it is expected that nonlinear squeezing can be further improved. The idea presented here can be readily extended to the higher-order phase gates [P. Marek et al., Phys. Rev. A 97, 022329 (2018)]. As such, this work presents an important step to extend the CV quantum information processing from Gaussian regime to non-Gaussian regime.