Distributed Quantum Multiparameter Estimation with Optimal Local Measurements

Area of Science:

• Quantum optics
• Quantum metrology
• Interferometry

Background:

• Mach-Zehnder interferometers (MZIs) are key quantum sensors.
• Achieving high sensitivity in multiparameter estimation is crucial.
• Nonclassical states can enhance quantum sensor performance.

Purpose of the Study:

• To investigate the multiparameter sensitivity bounds of a network of d Mach-Zehnder interferometers (MZIs).
• To determine if local measurements on MZIs can achieve the quantum Cramér-Rao bound.
• To compare the sensitivity of an entangled sensor network with independent MZIs.

Main Methods:

• Creating a d-mode entangled state by mixing a nonclassical state with vacuum states.
• Probing each MZI with a mode of the entangled state and a coherent state.
• Analyzing sensitivity bounds using local measurements and comparing with independent MZIs.

Main Results:

• Local measurements on the MZI network saturate the quantum Cramér-Rao bound.
• The sensor network overcomes the shot noise limit for estimating linear combinations of phase shifts.
• An entangled sensor network provides a sensitivity scaling of 1/n[over ¯]_{T}^{2}, offering a gain factor d over separable sensors.

Conclusions:

• A single nonclassical state in an entangled network achieves the same sensitivity as d nonclassical states in independent MZIs.
• The entangled protocol demonstrates a significant sensitivity advantage, especially for larger networks.
• This work highlights the power of entanglement for enhanced quantum sensing capabilities.