Quantum optical coherence can survive photon losses: a continuous-variable quantum erasure correcting code

TL;DR

This paper demonstrates the first experimental quantum erasure-correcting code that protects entangled light states from photon losses, enabling longer-distance quantum communication with fidelity surpassing classical limits.

Contribution

It introduces a practical, linear optics-based quantum erasure-correcting code that overcomes photon loss effects, a major challenge in quantum communication.

Findings

Successfully protects four-mode entangled states against erasures

Achieves transmission fidelities beyond classical limits

Demonstrates two approaches to mitigate in-line losses

Abstract

A fundamental requirement for enabling fault-tolerant quantum information processing is an efficient quantum error-correcting code (QECC) that robustly protects the involved fragile quantum states from their environment. Just as classical error-correcting codes are indispensible in today's information technologies, it is believed that QECC will play a similarly crucial role in tomorrow's quantum information systems. Here, we report on the first experimental demonstration of a quantum erasure-correcting code that overcomes the devastating effect of photon losses. Whereas {\it errors} translate, in an information theoretic language, the noise affecting a transmission line, {\it erasures} correspond to the in-line probabilistic loss of photons. Our quantum code protects a four-mode entangled mesoscopic state of light against erasures, and its associated encoding and decoding operations only require linear optics and Gaussian resources. Since in-line attenuation is generally the strongest limitation to quantum communication, much more than noise, such an erasure-correcting code provides a new tool for establishing quantum optical coherence over longer distances. We investigate two approaches for circumventing in-line losses using this code, and demonstrate that both approaches exhibit transmission fidelities beyond what is possible by classical means.