Quantum Correlation Resource Recycling via Sequential Measurements: Theoretical Models and Optical Experiments

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This review by Huang and co-workers is expertly written, clear, definitive and with a good amount of historic references and mentions of the latest literature. It was a pleasure to read. I highly reccommend publication in its current form - excellent job!

Comments on the Quality of English Language

Minor checks needed only

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The review titled Quantum Correlation Resource Recycling via Sequential Measurements: Theoretical Models and Optical Experiments is interesting. I have gone through the manuscript and would like to share with you my comments:

    Abstract:     

1.    It is highly recommended that a graphical abstract is added to summarise the review.  

    Introduction:

1.    For an outside reader, it seems that the authors used quantum entanglement and quantum correlation interchangeably.

2.    The authors must elaborate by drawing a line between the two based on the state. For instance, a pure state can present a completely equivalent entanglement and correlation.

3.    Please check Sen et al - https://doi.org/10.1088/1361-6633/aa872f. Hage et al - https://doi.org/10.1103/PhysRevLett.126.170404

Measurement:

2.    It is highly recommended that this section be reduced and summarised since this theoretical background can be found in any basic quantum computing/mechanics textbook.   

Bell Nonlocality Sharing: The Unsharp Measurement Formalism

1.    It is highly recommended that this section be reduced and summarised. The theoretical background of Quantum Steering and EPR Steering should be briefly discussed. Also, the title may be adjusted to include both.

Advances In Sequential Measurement Schemes For Quantum Correlation Recycling

1.    The authors need to elaborate further on Figure 2. a, explaining how the hierarchy was derived based on ref—no. 3 and 4.    

2.    A summary table is needed to list contributions, benefits, and challenges for each theoretical and experimental part.

3.    For example, one of the main obstacles comes from local measurements destroying the entanglement present in the state. Hence, there is a need for nondestructive measurement. Another example is the recycling of quantum correlation. Third is projective measurements, and so on.

Concluding Remarks and Outlook:

1.    The conclusion, remarks, and outlook are relatively general. For instance, the authors did not list all key challenges presented in previous sections, how they were tackled in theoretical and experimental work, and the discrepancies, if any – see the above section.

2.    Instead, some challenges were selected and highlighted. For example, adjusting the disturbance degree by designing weak measurement sequences.

3.    This phrase is misplaced at the end of this section (lines 702-703): “This review aims to summarize the relevant theoretical and experimental progress with an outlook in this field.” It needs to be removed or rephrased and placed at the beginning.  

4.    The authors need to elaborate further on “suitable measurement strategies,” providing more details in line with their cited references.     

Comments on the Quality of English Language

English is fairly accepted.  

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I am responding to MDPI request for me to provide you with a report in connection with the submitted manuscript “Quantum correlation resource recycling via sequential measurements: theoretical models and optical experiments” by Xianzhi Huang, Liyao Zhan, Liang Li, Suhui Bao, Zipeng Tao and Jiayu Ying . I am pleased to do so.

In this article, the authors have theoretically studied the interaction between quantum measurements and quantum correlations by designing appropriate measurement strategies, specifically, exploring the trade-off between information gain and disturbance degree in weak measurements to ensure that quantum correlations from the same source can be shared among multiple independent observers. Furthermore, they’ve reported the  experimental development process and the latest progress of the investigated topic. The research topic is very interesting, the presentation is very good and their results appear to be correct. The only comments are the following:

1)     In introduction section, authors do not describe any physical qbit structure. Could they make any mention related to the physical solid state qbits (spin, charge etc)? The authors could use articles e.g. Journal Phys.: Condens. Matter 30 455301 (2018), Phys. Rev. B 101, 165302 (2020) or any other paper.

2)     What is the importance of the current work in qbits technology (spin based qbit)?

3)     Could the authors analytically describe the nonlocality of their system (Bell nonlocality)? It seems that their description is quite short.

4)     What is the reason to perform their estimation with ε = π/2?

5)     What are the under investigation optical qubits?

6)     Please mention the “PPKTP”.

Comments on the Quality of English Language

...

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I have no further comments or suggestions. The revised manuscript looks good.