[Qirg] Review of draft-irtf-qirg-principles-02
VAN DEN BOSSCHE Mathias <mathias.van-den-bossche@thalesaleniaspace.com> Mon, 09 December 2019 09:49 UTC
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From: VAN DEN BOSSCHE Mathias <mathias.van-den-bossche@thalesaleniaspace.com>
To: "qirg@irtf.org" <qirg@irtf.org>
Thread-Topic: Review of draft-irtf-qirg-principles-02
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Date: Mon, 09 Dec 2019 09:48:56 +0000
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Subject: [Qirg] Review of draft-irtf-qirg-principles-02
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Dear all, I did some review work of draft-irtf-qirg-principles-02. The document is really well done, and the effort to non quantum readers is visible (and appreciated, even by a QFT-background guy like me). I introduce below (in basic ascii mode) a number of proposed changes/comments/questions to be discussed. Some are typos, some a clarifications, few are more fundamental. The idea is to fill the 'Discussion' and 'Decision' fields for each point. I let you go through it. We could maybe set a date to close this. All the best ! Mathias ==== Doc: draft-irtf-qirg-principles-02 ID : MVDB 01 Page/section: p 6/ § 3 Proposal/Question: I would change the title of §3 to _Entanglement as the fundamental resource_ Explanation: The fact is that a service is an action, while a resource is something you can create, quantify and manage. There is a targeted service is to "distribute entanglement". BTW the document mentions entanglement as a resource §§ 4.4.2.1 and 5.6.1, so that would improve consistency. Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 02 Page/section: p 7/ § 3 Proposal/Question: than -> then line 9 of p 7 Explanation: typo Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 03 Page/section: p 9/ § 4.2 Proposal/Question: change Any of the four Bell pair state above will do as it is possible .... to Any of the four Bell-pair states above will do, as it is possible .... Explanation: typo + some clarity Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 04 Page/section: p 10 / § 4.3 (last 3 lines) Proposal/Question: change The unknown quantum state that was transmitted never entered the network itself. Therefore, the network needs to only be able to reliably produce Bell pairs between any two nodes in the network. to change The unknown quantum state that was transmitted was never fed into network itself. Therefore, the network needs to only be able to reliably produce Bell pairs between any two nodes in the network, and perform BSM with external qbits to be transmitted. Explanation: * It is a delicate concept to explain that the network is here only to create a direct end-to-end link, which is then used directly by the end nodes without having the intermediate nodes to handle it. * The interface function (the BSM with external qbits) I think is still part of the network and should not be forgotten Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 05 Page/section: p 10 / § 4.4.1 Proposal/Question: The title could be _4.4.1 _Elementary link generation_ instead. The expected contribution should include at least 3 main parts * Create the BPS * Store the entangled members of non-local BPS * Monitor the entanglement resource level on each link Explanation The other aspects of entanglement life cycle are well described in the subsequent sections, it looks like this one is dedicated to elementary links, right? Everyone will have in mind the function to create BPS across the elementary links, but we should first not forget the fact that they need be stored (esp. in the light of the asynchronous use mentioned further in the document). And then this stored entanglement will be the resource to be monitored on each elementary link, because it will be consumed and it will expire (by decoherence). Monitoring will detect low levels and trigger regeneration. Can we agree on that before developing further? Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 07 Page/section: p 11 / § 4.4.2 Proposal/Question: Augment The problem with generating entangled pairs directly across a link is that its efficiency decreases with its length. Beyond a few 10s of kms the rate is effectively zero and due to the no-cloning theorem we cannot simply amplify the signal. The solution is entanglement swapping. with The problem with generating entangled pairs directly across a link is that its efficiency decreases with its length. Beyond a few 10s of kms in optical fibre or 1000s of kms in free space [ESA, Micius], the rate is effectively zero and due to the no-cloning theorem we cannot simply amplify the signal. The solution to propagate entanglement at large distances is entanglement swapping. Explanation: The two kinds of links (fibre & free space) shall be mentioned for completeness. They are not competing, rather complementary, and both will require swapping and routing devices anyway. Free-space to satellites will allow having fewer nodes on the path, the goal being to improve capacity. Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 08 Page/section: p 12 / § 4.4.2 Proposal/Question: Add at the end of the section: << Entanglement swapping allows entanglement to exist at larger distances than what the entangled degrees of freedom can propagate. Yet one should keep in mind that the capacity of the network still decreases with the number of swapping nodes (all other parameters being kept fixed). So entanglement swapping solves the problem of existence of long distance entanglement, but not that of performance of the end-to-end link. >> Explanation: This - clarifies the role of entanglement swapping in the network as a system - allows identifying different way of attacking the problem of performance. Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 09 Page/section: p 12 / § 4.4.2.2 Proposal/Question: Change 2. An identifier that allows the application to unambiguously determine which qubits at the two end-points belong to which entangled pair. to 2. An identifier that allows the applicatqion to unambiguously determine which qubits at the two end-points belong to which entangled pair (including end-point identification). Explanation: For more clarity Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 10 Page/section: p 12 / § 4.4.2.2 Proposal/Question: Add 4. An estimate of the expiry date of the BSP. Explanation: It might not be relevant in the first networks where decoherence will require fast consumption of the created entanglement resource, but we hope that this constraint will be relaxed, and that this will become a relevant network management information. Alternatively create a §4.4.2.3 on entanglement storage Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 11 Page/section: p 13ff / § 5 Proposal/Question: >From that point on, the document mentions abundantly the term of 'repeaters'. I recommend to give it up and use a more accurate term such as swapper or router (that are introduced in the document) or propagator (that's my QFT background). Explanation I know the term is pretty much used already, but here is my argument. Although it is a convenient term for those who have a classical network background (where it is fairly transparent), it is abusive in the case of entanglement networks. The fact is that nothing is repeated, it is just blank entanglement that is forwarded, swapped, propagated commuted (as in the old telephone systems where an operator had to plug a wire between two lines nodes to connect two network segments and allow an end-to-end line to exist). It repeats no data (as the considerations at the end of the document insist on). Using the term of repeater is confusing, and leads to wrong understanding and then inadequate decisions. Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 12 Page/section: p 14 / § 5.1 (3.) Proposal/Question: Change This implies ... store temporary state as the ... to This implies ... store the received temporary state as the ... Explanation: If I understand the sentence right. Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 14 Page/section: p 18 / § 5.5.1 Proposal/Question: Change "The memory lifetime depends on the particular physical setup, but the highest achievable values currently are on the order of seconds." to "The memory lifetime depends on the particular physical setup. This is object of intense research. Current setups achieve lifetime up to the order of seconds, but promising approaches should allow a significant expansion of this value" Explanation: I came across a paper [Nature _517_, 177 (2015)] that claimed 6h coherence time with Europium ion spins that are "optically addressable". Since I am no experimentalist, I do not know what intricacies this setup might require. I do not know either whether this result is object of controversy. But if this is not the case, I would suggest changing the text to something less hard on memory lifetimes. Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 15 Page/section: p 18 (and 19) / § 5.5.1 (and 5.5.2) Proposal/Question: Explain why it might be more cost efficient to use short lifetimes. Explanation: It might be a valid choice, but it deserves motivation. Do not forget that anything expensive produced in mass figures becomes inexpensive. Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 16 Page/section: p 18 / § 5.5.2 Proposal/Question: It is not clear what the mentioned success rate of 1e-3 addresses. I understand it is the rate of success to create a BPS by pumping a non-linear crystal with a suitable pump. Is it this? Or is it the probability that BSM effectively entangles 2 BPS? Or is it something else? It is tempting with this figure to compute the capacity of an n-hop path. But is they the correct needed information? Explanation: See above Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 17 Page/section: p 21 / § 5.6.1 (5.) Proposal/Question: I propose to remove the considerations on QKD, or at least to reduce them drastically. Explanation: There might be other solutions to secure the control plane other than QKD. It is true that once optical links are available, it is tempting to implement QKD protocols, but is it the right moment to highlight a particular solution? Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 18 Page/section: p 22 / § 5.6.2 (3.) Proposal/Question: Change "This point is crucial in enabling the reuse of resources of a network and (...)" to "This point is crucial in optimising the use of entanglement resources of a network and (...)" Explanation: If I understand right, this is clearer. Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 19 Page/section: p 24 / § 5.6.2 (6.) Proposal/Question: Question : do you consider parallelising over the same path with e.g. multiplexed optical channels, or do you consider also parallelising over different paths? In which case it could be mentioned. Explanation: N/A Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 20 Page/section: p 24 / § 5.6.2 (7.) Proposal/Question: I would suggest giving synchronisation accuracy needs here. Not necessarily the figure but a least the relationship with the source rate etc. Explanation: This would allow assessing what is feasible and what is not. At some point, synchronisation may be much more demanding than what you can do with GNSS (~ 0.1 ns). As a matter of fact, the network its might become itself a big machine to measure the metric of space time on Earth... Discussion: TBD Decision: TBD --- Doc: draft-irtf-qirg-principles-02 ID : MVDB 21 Page/section: p 24 / § 6 Proposal/Question: Change "Even though no user data enters a quantum network security is listed as an explicit goal (...)" to "Even though no user data enters a quantum network, security is listed as an explicit goal (...)" Explanation: Typo Discussion: TBD Decision: TBD [@@ THALES ALENIA SPACE INTERNAL @@]
- [Qirg] Review of draft-irtf-qirg-principles-02 VAN DEN BOSSCHE Mathias
- Re: [Qirg] Review of draft-irtf-qirg-principles-02 Gelard Patrick
- Re: [Qirg] Review of draft-irtf-qirg-principles-02 Rodney Van Meter
- Re: [Qirg] Review of draft-irtf-qirg-principles-02 VAN DEN BOSSCHE Mathias
- Re: [Qirg] Review of draft-irtf-qirg-principles-02 Gelard Patrick
- Re: [Qirg] Review of draft-irtf-qirg-principles-02 VAN DEN BOSSCHE Mathias
- Re: [Qirg] Review of draft-irtf-qirg-principles-02 VAN DEN BOSSCHE Mathias
- Re: [Qirg] Review of draft-irtf-qirg-principles-02 Wojciech Kozlowski
- Re: [Qirg] Review of draft-irtf-qirg-principles-02 Wojciech Kozlowski