Entanglement-Enhanced Phase Estimation without Prior Phase Information

Area of Science:

• Quantum optics
• Atomic physics
• Quantum metrology

Background:

• Quantum squeezed states are crucial for enhancing measurement precision.
• Quantum nondemolition (QND) measurement is a technique for measuring quantum systems without collapsing their state.
• Planar quantum squeezed (PQS) states offer potential for improved phase estimation.

Purpose of the Study:

• To generate and characterize planar quantum squeezed (PQS) states using QND measurement on an ensemble of $^{87}$Rb atoms.
• To evaluate the metrological performance of generated PQS states for single-shot phase estimation.
• To identify the role of entanglement in the observed metrological advantage.

Main Methods:

• Utilized quantum nondemolition (QND) measurement on an ensemble of $^{87}$Rb atoms with a Poissonian atom number distribution.
• Precisely calibrated QND measurement to infer the conditional covariance matrix of PQS states.
• Applied spin squeezing inequalities to analyze the contribution of spin-spin entanglement.

Main Results:

• Successfully generated PQS states exhibiting dual squeezing characteristics.
• Demonstrated a metrological advantage of at least 3.1 dB for arbitrary phase estimation compared to classical states.
• Showed that PQS states outperform single-component-squeezed states for most phase angles.

Conclusions:

• Spin-spin entanglement within the generated PQS states is responsible for the observed metrological advantage.
• PQS states generated via QND measurement are a promising resource for high-precision phase estimation.
• The study validates the theoretical proposals for using PQS states in metrology.