Optimal Gain Sensing of Quantum-Limited Phase-Insensitive Amplifiers

Area of Science:

• Quantum optics
• Quantum information science
• Optical amplifier metrology

Background:

• Phase-insensitive optical amplifiers are crucial for quantum technologies.
• Precisely estimating amplifier gain is essential for quantum sensing and information processing.

Purpose of the Study:

• To determine the quantum limit on gain estimation precision for quantum-limited phase-insensitive amplifiers.
• To investigate the role of probe properties (photon number, modes) and entanglement in optimal gain sensing.

Main Methods:

• Utilized a multimode probe, potentially entangled with an ancilla system.
• Analyzed quantum-optimal pure-state probes diagonal in the number basis.
• Compared quantum probe performance with classical probes using photon-counting estimators.

Main Results:

• Photon number (N) and number of modes (M) are equivalent and interchangeable resources for optimal gain sensing.
• Identified a class of quantum-optimal probes for gain estimation.
• Demonstrated a quantum advantage for gain sensing, even with single-photon probes and inefficient detection.

Conclusions:

• The study establishes fundamental limits for quantum amplifier gain estimation.
• Highlights the flexibility of using photon number or modes as resources for enhanced sensing.
• Confirms the practical utility of quantum probes in realistic, noisy detection scenarios.