Lengthening Transmission Distance of Continuous Variable Quantum Key Distribution with Discrete Modulation through Photon Catalyzing
Round 1
Reviewer 1 Report
The main results of the work are obtained on the basis of numerical calculations in accordance with Eqs. (5) and (7), which are written without any proof and the appropriate calculation.
Sec. 2 is written very sloppy. Known results are given without adequate references, and contain many inaccuracies and errors. Therefore, the meaning of the new element (ZPC) in the chain is not explained.
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Reviewer 2 Report
This manuscript studies a ZPC-based DM-CVQKD(zero-photon catalysis-based discretely modulated continuous variable quantum key distribution) to improve the transmission distance together with tolerating higher excess noise and lower reconciliation efficiency.
One of the main issues of QKD is a long-distance protocol, and CVQKD is regarded as a good candidate as we may deploy an advantages of the modern telecommunications technologies. In this sense, this manuscript deals with an important topic.
However, I cannot recommend the publication of this manuscript with the current version. To put it very simply, the current version lacks detailed descriptions to judge its acceptance. Thus, I couldn't get the main messages the authors would like to insist with their results. A detailed report is as follows. I tried to explain point to point from Introduction.
At page 1 in Introduction: the sentence "In DM-CVQKD it generates ..." should be updated. I didn't get a point of the benefits for using nonorthogonal coherent states. What is the role of the DM?
At page 2, 1st paragraph: 1) how the photon catalyzing operation increase the entanglement degree? and 2) what does it mean that entanglement-based systems is equivalent to the prepare-and-measure system? And 3) a description of SNR is missing.
At page 3: 1) In the EB version, what type of pure bipartite state need to be prepared? entangled state? CV or DV systems? which basis states? 2) how to control the variance of such state? 3) What is the Z_k in Eq. (1)? 4) in the 1st sentence in Sec. 2.2, the authors mentioned "... can improve the practical quantum system [21]." But, this should be written clearly, e.g., improve SOMETHING... 5) in Fig 2., does any physical explanations of higher (lower) Z_k values over increasing V_A?
At page 5: 1) is there any specific reason Alice perform heterodyne detection? 2) in the same paragraph, what does the "source enhancement" mean?
At page 6: 1) the authors discussed numerical calculations for specific conditions e.g., a reconciliation efficiency of 90% and so on. Where do such values come form? 2) I don't understand why the authors compare two different detections which resulted in Fig. 6(a) 3) Please check the correctness of the colors and the cases in Fig. 6(b). It seems that the descriptions are mismatch between figure and the main text.
Author Response
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Reviewer 3 Report
This paper suggests possible performance improvement by using the discrete modulation (DM) together with photon catalysis (PC) and zero-PC (ZPC) to get the extended maximal transmission distance and increased secret key rate of continuous variable Quantum Key Distribution (CV-QKD).
The PC technique to improve the performance of CV-QKDs had been shown elsewhere. However, the techniques PC and ZPC to be used with DM-CV-QKD seems to be a novel approach.
The theory and numerical results have been shown as the proof for the main conclusions. The presentation of the theory and the simulation results has not been clearly presented. The figures are not well introduced within the text.
The paper brings the novelty and shows the performance improvement. Therefore, it is recommended for publication. However, several important issues should be correctly addressed. Please check bellow complete list.
Comments for author File: Comments.pdf
Author Response
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Round 2
Reviewer 1 Report
Now the manuscript is written more clearly and accurately.
However, there are still a number of inaccuracies
- On page 4 after Eq. 4 the approval |\psi>in = |\psi>out for \tau=1 is not obvious because a dependence of functions and operators on \tau is not shown.
- In App. B the Hilbert spase in Eq.22 and in the following text is marked with different letters.
Author Response
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Reviewer 2 Report
The authors replied all my comments and tried to improve the manuscript faithfully.
Still, I don’t understand some parts clearly how it works and so on, but I think the authors provided enough references and those issues will be discussing in the community.
One last minor comment:
It was written that the photon catalyzing operation can be used to increase the degree of entanglement of two-mode squeezed states and such operation is non-Gaussian.
As the authors may know, the two-mode squeezed vacuum states is one of the well known two-mode Gaussian states. Thus, applying such non-Gaussian operation transforms the Gaussian entangled state to non-Gaussian one. Apart from this, it was shown that two-mode squeezed vacuum states can be detected more effectively in low squeezing by applying only Gaussian operations such as displacement, rotation and local squeezing operations. See the following Refs.
[1] Journal of Modern Optics 57, 1550-1554 (2010): by only using local Gaussian operations for better quantum violations
[2] Phys. Rev. A 84, 012302 (2011): another reference by using local Gaussian operations for better quantum violations
[3] Phys. Rev. A 92, 012318 (2015): another reference by using catalysis
I am wondering that the authors considered Gaussian operations instead of non-Gaussian ones for the authors’ purpose, a better QKD protocol. If not, I would see whether there are any differences.
Author Response
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