Quantum feedback for measurement and control

About this Video

• Video Title: Quantum feedback for measurement and control
• Channel: Institut Henri Poincaré
• Speakers: (Speaker name not explicitly mentioned in the transcript)
• Duration: 00:51:15

Introduction

This video lecture discusses quantum feedback for measurement and control, focusing on continuous measurement and open quantum systems. The speaker explores the unique aspects of quantum measurement, highlighting how measurement back-action, typically considered detrimental, can be beneficial for control. The lecture covers both theoretical frameworks and experimental implementations of adaptive measurement for phase estimation and entanglement generation.

Key Takeaways

1. Quantum Measurement Distinctiveness: Quantum measurements differ fundamentally from classical measurements. The measurement method significantly impacts the information acquired, and the act of measurement inherently disturbs the quantum state.
2. Continuous Measurement and Back-Action: Unlike idealized instantaneous projections, realistic measurements involve interactions with finite timescales. This "back-action" can be observed and utilized for feedback control.
3. Adaptive Measurement: The optimal measurement basis for a given quantity can change dynamically based on previous measurement outcomes and system evolution, improving measurement precision. This is demonstrated experimentally for phase measurement.
4. Quantum Feedback Protocols: A general method for deriving quantum feedback protocols is presented, allowing for the design of strategies to prepare target quantum states. This approach is applied to entanglement generation and Dicke state preparation.
5. Average Sense Optimality: For systems with many quantum elements, an "average sense optimality" approach simplifies feedback control by averaging over possible measurement outcomes, making the process computationally tractable while maintaining high fidelity.