Multi-step two-copy distillation of squeezed states via two photon subtraction

TL;DR

This paper demonstrates a novel multi-step distillation process for Gaussian squeezed states suffering from photon loss, enhancing their squeeze factor and potential quantum advantages through experimental photon subtraction and Gaussification.

Contribution

First experimental demonstration of multi-step distillation of Gaussian squeezed states with photon loss, improving squeeze factor via photon subtraction and Gaussification protocols.

Findings

Squeeze factor improved from 2.4 dB to 2.8 dB after photon subtraction.

Further improved to 3.4 dB using Gaussification.

Distillation steps can be increased with longer data sampling without extra hardware.

Abstract

Squeezed states of light have been improving the sensitivity of gravitational-wave observatories and are nonclassical resources of quantum cryptography and envisioned photonic quantum computers. The higher the squeeze factor is, the higher is the quantum advantage. Almost all applications of squeezed light require multi-path optical interference, whose unavoidable imperfections introduce optical loss, degrade the squeeze factor, as well as the quantum advantage. Here, for the first time, we experimentally demonstrate the distillation of Gaussian squeezed states that suffered from Gaussian photon loss. Our demonstration already involves two distillation steps. The first step improved the squeeze factor from 2.4 dB to 2.8 dB by the subtraction of two photons. The second step improved the value from 2.8 dB to 3.4 dB by a Gaussification protocol. It was realised on data measured at different times via an 8-port balanced homodyne detector and via data post-processing. The number of distillation steps can be increased by longer data sampling times, without additional hardware. We propose and discuss the application to quantum cryptography and photonic quantum computers.