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Related Experiment Video

Updated: Oct 13, 2025

In Situ Measurement of Vacuum Window Birefringence using 25Mg+ Fluorescence

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Direct Characterization of Quantum Measurements Using Weak Values.

Liang Xu^1,2, Huichao Xu^1,3, Tao Jiang¹

¹National Laboratory of Solid State Microstructures, Key Laboratory of Intelligent Optical Sensing and Manipulation, College of Engineering and Applied Sciences, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.

Physical Review Letters

|November 12, 2021

Summary

Researchers developed a new method for directly characterizing quantum measurement apparatuses. This technique utilizes the backward direction of weak measurement formalism for enhanced accuracy and precision in quantum state tomography.

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Area of Science:

Quantum mechanics
Quantum information science
Metrology

Background:

Weak measurement formalism offers unique features for quantum state tomography.
Existing methods for characterizing measurement apparatuses can be complex.
A direct tomography of measurement apparatuses is desirable for improved quantum technologies.

Purpose of the Study:

To propose and experimentally demonstrate a direct tomography protocol for quantum measurement apparatuses.
To leverage the time-symmetric formalism of weak measurements for apparatus characterization.
To enhance the accuracy and precision of quantum measurement characterization.

Main Methods:

Utilizing the backward direction of the weak measurement formalism.
Implementing a protocol for direct tomography of measurement apparatuses.
Applying arbitrary measurement strengths for improved accuracy.
Incorporating the completeness condition of measurement operators.

Main Results:

Successful experimental demonstration of direct tomography for a measurement apparatus.
Protocol achieves improved accuracy and precision with arbitrary measurement strengths.
Completeness condition enhances precision and ensures protocol feasibility for arbitrary quantum measurements.

Conclusions:

The study provides a novel and efficient method for characterizing quantum measurement apparatuses.
New insights into the symmetry between quantum states and measurements are offered.
The developed protocol advances quantum state tomography and metrology.