Entanglement-Assisted Absorption Spectroscopy

TL;DR

This paper presents a practical quantum spectroscopy system using entanglement that significantly outperforms classical methods in detecting absorption spectra, with robustness to noise and loss, enabling near-term experiments.

Contribution

The authors design a novel entanglement-assisted spectroscopy scheme that achieves quantum advantage over classical methods in absorption detection tasks.

Findings

Orders-of-magnitude lower error probability than classical systems.

Achieves quantum-optimal performance in absorption line detection.

Robust against noise and loss, suitable for near-term experiments.

Abstract

Spectroscopy is an important tool for probing the properties of materials, chemicals and biological samples. We design a practical transmitter-receiver system that exploits entanglement to achieve a provable quantum advantage over all spectroscopic schemes based on classical sources. To probe the absorption spectra, modelled as pattern of transmissivities among different frequency modes, we employ broad-band signal-idler pairs in two-mode squeezed vacuum states. At the receiver side, we apply photodetection after optical parametric amplification. Finally, we perform a maximal-likehihood decision test on the measurement results, achieving orders-of-magnitude-lower error probability than the optimum classical systems in various examples, including `wine-tasting' and `drug-testing' where real molecules are considered. In detecting the presence of an absorption line, our quantum scheme achieves the optimum performance allowed by quantum mechanics. The quantum advantage in our system is robust against noise and loss, which makes near-term experimental demonstration possible.