Experimental beating the standard quantum limit under non-markovian dephasing environment

TL;DR

This paper demonstrates that in a non-Markovian dephasing environment, entangled GHZ states can surpass the standard quantum limit, showing a scalable advantage in quantum metrology using a controlled photonic system.

Contribution

The study experimentally shows that non-Markovian dephasing allows entangled states to beat the SQL, unlike in Markovian environments, highlighting a universal approach for quantum metrology.

Findings

GHZ states surpass SQL in non-Markovian environment

Quadratic decay behavior enables scalability up to six photons

Results suggest a universal method for real-world quantum metrology

Abstract

Entanglement enhanced quantum metrology has been well investigated for beating the standard quantum limit (SQL). However, the metrological advantage of entangled states becomes much more elusive in the presence of noise. Under strictly Markovian dephasing noise, the uncorrelated and maximally entangled states achieve exactly the same measurement precision. However, it was predicted that in a non-Markovian dephasing channel, the entangled probes can recover their metrological advantage. Here, by using a highly controlled photonic system, we simulate a non-Markovian dephasing channel fulfill the quadratic decay behaviour. Under such a channel, we demonstrate the GHZ states can surpass the SQL in a scaling manner, up to six photons. Since the quadratic decay behavior is quite general for short time expansion in open quantum systems (also known as the quantum Zeno effect), our results suggest a universal and scalable method to beat the SQL in the real-word metrology tasks.