Optimal multi-photon phase sensing with a single interference fringe

TL;DR

This paper demonstrates that using the Holland-Burnett state with a single interference fringe can surpass the shot noise limit in phase sensing, offering a simpler alternative to complex parity measurements for quantum-enhanced optical phase measurements.

Contribution

The study shows that the Holland-Burnett state outperforms NOON states for N > 4 in phase sensitivity and experimentally achieves three times below the shot noise limit with a six-photon fringe.

Findings

Holland-Burnett state is optimal for N > 4.

Single fringe measurement surpasses shot noise limit.

Experimental demonstration with six-photon Holland-Burnett state.

Abstract

Quantum entanglement can help to increase the precision of optical phase measurements beyond the shot noise limit (SNL) to the ultimate Heisenberg limit. However, the N-photon parity measurements required to achieve this optimal sensitivity are extremely difficult to realize with current photon detection technologies, requiring high-fidelity resolution of N+1 different photon distributions between the output ports. Recent experimental demonstrations of precision beyond the SNL have therefore used only one or two photon-number detection patterns instead of parity measurements. Here we investigate the achievable phase sensitivity of the simple and efficient single interference fringe detection technique. We show that the maximally-entangled "NOON" state does not achieve optimal phase sensitivity when N > 4, rather, we show that the Holland-Burnett state is optimal. We experimentally demonstrate this enhanced sensitivity using a single photon-counted fringe of the six-photon Holland-Burnett state. Specifically, our single-fringe six-photon measurement achieves a phase variance three times below the SNL.