Experimental demonstration of Gaussian boson sampling with displacement

TL;DR

This paper demonstrates a Gaussian boson sampling machine with displacement, enabling new state reconstruction and analyzing classical light effects on sampling complexity, advancing practical quantum sampling technologies.

Contribution

The work introduces displacement in GBS, allowing in situ Gaussian state reconstruction and semi-classical modeling to reduce computational complexity.

Findings

Successfully implemented displacement in GBS with a 15-mode interferometer.

Developed a three-measurement technique for Gaussian state reconstruction.

Validated semi-classical models that simplify sampling when classical light is present.

Abstract

Gaussian boson sampling (GBS) is quantum sampling task in which one has to draw samples from the photon-number distribution of a large-dimensional nonclassical squeezed state of light. In an effort to make this task intractable for a classical computer, experiments building GBS machines have mainly focused on increasing the dimensionality and squeezing strength of the nonclassical light. However, no experiment has yet demonstrated the ability to displace the squeezed state in phase-space, which is generally required for practical applications of GBS. In this work, we build a GBS machine which achieves the displacement by injecting a laser beam alongside a two-mode squeezed vacuum state into a 15-mode interferometer. We focus on two new capabilities. Firstly, we use the displacement to reconstruct the multimode Gaussian state at the output of the interferometer. Our reconstruction technique is in situ and requires only three measurements settings regardless of the state dimension. Secondly, we study how the addition of classical laser light in our GBS machine affects the complexity of sampling its output photon statistics. We introduce and validate approximate semi-classical models which reduce the computational cost when a significant fraction of the detected light is classical.