GHZ protocols enhance frequency metrology despite spontaneous decay

Area of Science:

• Quantum Metrology
• Atomic Clocks
• Quantum Information Science

Background:

• Correlated quantum states and measurements offer potential improvements in frequency metrology and atomic clock stability.
• Developing noise-robust strategies against dominant noise processes like decoherence remains a significant challenge in quantum technologies.

Purpose of the Study:

• To address decoherence caused by spontaneous decay in quantum metrology.
• To investigate the effectiveness of Greenberger-Horne-Zeilinger (GHZ) states combined with correlated measurements and nonlinear estimation for enhancing atomic clock performance.

Main Methods:

• Utilized Greenberger-Horne-Zeilinger (GHZ) states for quantum measurements.
• Implemented a correlated measurement strategy.
• Employed a nonlinear estimation technique to process measurement outcomes.
• Conducted comprehensive Monte Carlo simulations of atomic clocks to assess protocol robustness.

Main Results:

• Achieved sensitivity gains of up to 2.25 decibel in the presence of decoherence due to spontaneous decay.
• Demonstrated performance comparable to fundamental bounds for systems with up to approximately 80 atoms.
• Identified that the gain originates from a veto signal that detects and mitigates errors from spontaneous emission events.
• Observed no enhancement under dephasing noise, highlighting the specific benefit against spontaneous decay.

Conclusions:

• The proposed GHZ state protocol offers a robust method for improving atomic clock accuracy and frequency metrology in the presence of spontaneous decay.
• The veto signal mechanism is crucial for mitigating errors and achieving quantum-enhanced metrology.
• This work demonstrates the practical advantages of specific quantum strategies for overcoming noise limitations in quantum sensors.