Re: [Qirg] renewing I-Ds: comments, please!

Wojciech Kozlowski <W.Kozlowski@tudelft.nl> Fri, 06 September 2019 16:05 UTC

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From: Wojciech Kozlowski <W.Kozlowski@tudelft.nl>
To: "qirg@irtf.org" <qirg@irtf.org>
Thread-Topic: [Qirg] renewing I-Ds: comments, please!
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Date: Fri, 06 Sep 2019 16:05:41 +0000
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Subject: Re: [Qirg] renewing I-Ds: comments, please!
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Thanks for your feedback. I didn't have time to address all your points, but I have some comments inline:

On Wed, 2019-09-04 at 14:45 +0000, Gelard Patrick wrote:
2/ It is written that :

However, it is impossible to entangle two qubits without ever having them directly interact with each other (e.g. by performing a local two-qubit gate, such as the CNOT)


Does this sentence not contradict the paragraph “4.3.3.  Bell Pair links and entanglement swapping”   ? Because with entanglement swapping it is possible to entangle two qubits that never directly interact with each other : https://arxiv.org/abs/quant-ph/0409093 !!!

This is a very good point and it just shows the draft needs some extra care with the language. I guess the best way to clarify this point is that entanglement swapping doesn't actually create entanglement. Instead one of the particles is simply teleported to a more distant location. I haven't addressed this point in the latest version though.


3/ To achieve teleportation, a Bell Pair needs to be distributed between the source and destination. Thus to teleport a Qubit we need first to distributed a Bell Pair and also use two classical bit. This is not a very effective type of communication because it is consume more resource than the one is transmit, isn’t it ? !!!


It doesn't consume more resources, because we are not interested in transmitting classical data. Qubits are teleported for the purposes of sharing quantum states and entanglement (for use by higher-layer applications), something you cannot do by simply transmitting classical bits.


4/ 5.3.1.  Goals of a quantum internet.

-          Support distributed quantum applications and Support tomorrow's distributed quantum applications. For example concerning the QKD, there is a great zoology of QKD algorithms ( https://arxiv.org/pdf/1906.01645.pdf ) not necessarily based on the same quantum phenomenon (Heisenberg's uncertainty principle, entanglement) and require different characteristic of quantum channel.   Can an internet quantum communication infrastructure take into account this diversity of needs?

Adding references is a pain to do in the XML format for drafts so I haven't added this reference. I would also add a reference to https://wiki.veriqloud.fr/index.php?title=Main_Page


5/ 5.3.2.  The principles of a quantum internet.


-          Bell Pairs are the fundamental building block. Distributed quantum computation need multipartite entangled states shared among several nodes of the network and thus more than  Bell Pairs, isn’t it ? Or the goal is to transforming multipartite entangled states into the tensor product of bipartite Bell pairs between specific nodes using only a certain class of local operations and classical communication ( https://arxiv.org/abs/1907.08019 ) ?


I'm not sure I follow this point. You can create more complex entangled states from Bell Pairs.