Passive Environment-Assisted Quantum Communication

TL;DR

This paper investigates how passive environment assistance, using various ancilla states, can improve quantum communication over bosonic pure-loss channels, especially when transmissivity is low, by exploring practical non-Gaussian states and strategies.

Contribution

It introduces a framework for passive environment-assisted quantum communication, analyzing non-Gaussian ancilla states and developing analytical schemes for high-fidelity transmission.

Findings

Passive assistance enhances quantum capacity below 50% transmissivity.

Non-Gaussian ancilla states like Fock and cat states improve transmission fidelity.

Analytical schemes achieve high-fidelity and efficient information transfer.

Abstract

As quantum information systems mature, efficient and coherent transfer of quantum information through noisy channels becomes increasingly important. We examine how passive environment-assisted quantum communication enhances direct quantum information transfer efficiency. A bosonic pure-loss channel, modeled as transmission through a beam splitter with a vacuum input state at the dark port, has zero quantum capacity when transmissivity is below 50%. Quantum communication through the channel can be enhanced by passive environment assistance, achieved via the selection of an appropriate input state for the ancilla port. Although ideal Gottesman-Kitaev-Preskill (GKP) states enable perfect quantum information transmission at arbitrarily small transmissivity, they are challenging to realize experimentally. We therefore explore more experimentally accessible non-Gaussian ancilla states, such as Fock, cat, and squeezed cat states, and numerically determine the optimal encoding and decoding strategies. We also construct analytical schemes that yield high-fidelity transmission and good information rates.