Beating the Standard Quantum Limit with Four Entangled Photons

TL;DR

This paper demonstrates that four entangled photons can be used to surpass the standard quantum limit in optical phase measurements, enabling higher precision in various scientific applications.

Contribution

The authors experimentally show that four-photon entanglement can achieve interference visibility beyond the classical limit, advancing quantum metrology techniques.

Findings

Entangled four-photon interference exceeds the standard quantum limit

Demonstration of high-visibility quantum interference

Potential for improved high-precision measurements

Abstract

Precision measurements are important across all fields of science. In particular, optical phase measurements can be used to measure distance, position, displacement, acceleration and optical path length. Quantum entanglement enables higher precision than would otherwise be possible. We demonstrate an optical phase measurement with an entangled four photon interference visibility greater than the threshold to beat the standard quantum limit--the limit attainable without entanglement. These results open the way for new high-precision measurement applications.