Quantum Advantage with Seeded Squeezed Light for Absorption Measurement

TL;DR

This paper demonstrates a practical scheme using seeded squeezed light to perform absorption measurements with sensitivity beyond the shot-noise limit, achieving over 1.2 dB quantum advantage at faint absorption levels.

Contribution

The work introduces a feasible method for sub-shot-noise absorption measurement using seeded four-wave mixing in rubidium vapor, surpassing classical sensitivity limits.

Findings

Achieved over 1.2 dB quantum advantage in sensitivity.

Demonstrated sub-shot-noise absorption measurement without complex detection schemes.

Theoretical analysis indicates a corrected quantum advantage of 3 dB.

Abstract

Absorption measurement is an exceptionally versatile tool for many applications in science and engineering. For absorption measurements using laser beams of light, the sensitivity is theoretically limited by the shot noise due to the fundamental Poisson distribution of photon number in laser radiation. In practice, the shot-noise limit can only be achieved when all other sources of noise are eliminated. \textcolor{black}{Here, we use seeded squeezed light to demonstrate that direct absorption measurement can be performed with sensitivity beyond the shot-noise limit. We present a practically realizable scheme, where intensity squeezed beams are generated by a seeded four-wave mixing process in an atomic rubidium vapor cell. More than 1.2~dB quantum advantage for the measurement sensitivity is obtained at faint absorption levels ($\leq 10\%$). We also present a detailed theoretical analysis to show that the observed quantum advantage when corrected for optical loss would be equivalent to 3~dB. Our experiment demonstrates a direct sub-shot-noise measurement of absorption that requires neither homodyne/lock-in nor logic coincidence detection schemes. It is therefore very applicable in many circumstances where sub-shot-noise-level absorption measurements are highly desirable.