Quantum Internet Research Group                        O. van Deventer 
Internet Draft                                                    TNO 
Intended status: Informational                             J.T. Vogel 
Expires: July 2026                                                TNO 
                                                            O. Ubbens 
                                                                  TNO 
                                                          E. Aguilera 
                                                                  TNO 
                                                      January 30, 2026 
 
                                      
       RFC9583 Clock Sync is not a valid Quantum-Internet Application 
                       draft-vandeventer-qirg-rfc9583-qcs-internet-00


Status of this Memo 

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Abstract 

   This internet draft is a critique of RFC 9583, "Application 
   Scenarios for the Quantum Internet". Section 3.2 of that document 
 
 
 
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   presents network clock synchronization as application for quantum 
   internet. The present internet draft argues why it is not. 

Table of Contents 

   1. Introduction...................................................2
   2. Quantum Clock Synchronization..................................3
   3. Matter-based entanglement requires slow clock transport........4
   4. Photon-based entanglement does not carry time information......4
   5. No known method can create the required initial conditions 
   without already synchronized clocks...............................5
   6. Current synchronization solutions suffice......................6
   7. Security Considerations........................................6
   8. IANA Considerations............................................6
   9. Conclusions....................................................6
   10. Informative references........................................6
   11. Acknowledgments...............................................7
   Appendix A. Discussion of other references........................8
      A.1. [Ilo-Okeke]...............................................8
      A.2. [Komar]...................................................8
      A.3. [Guo].....................................................8
    
1. Introduction 

   Quantum communication is attracting major investments worldwide. In 
   Europe alone, hundreds of millions of euros are being invested in 
   quantum communication infrastructure, including EuroQCI with a focus 
   on quantum key distribution (QKD), and satellite-based quantum 
   communication. Many of those investments are made with a long-term 
   vision towards a "full" quantum internet. [RFC9583] describes a 
   possible quantum-internet development in six stages, as well as 
   applications and application scenarios. 

   We studied the QIRG document [RFC9583] in order to validate quantum-
   internet investments of our own. We found that most applications are 
   less than convincing. Many of the applications could easily be 
   implemented with much cheaper existing technologies. The viability 
   controversies of QKD are well known [Aquina]. Other application 
   scenarios are still at low technology readiness level, like 
   distributed quantum computing. 

   One application stood out to us, namely network clock 
   synchronization. This application is easily explainable. Moreover, 
   it would provide a potential improvement of a high-value classic 
   application. In order to better understand the quantum-internet 
   application, we involved mathematicians, electrical engineers and 
   physicists of our own organisation, and we consulted with external 
 
 
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   specialists on clock synchronization and quantum technologies, 
   including some of the original authors. Despite these efforts, we 
   have been unable to refute the null hypothesis, namely that quantum 
   clock synchronization is not a valid application of quantum 
   internet. 

   This internet draft introduces quantum clock synchronization, and it 
   provides four arguments for the "not-valid" conclusion. 

   NOTE: 

   The term "synchronisation" has multiple meanings in scientific 
   literature. 

   Meaning 1: ("clock synchronization"): adjustment of a clock or watch 
   to show the same time as another. 

   Meaning 2 ("synthonization"): the process of setting two or more 
   oscillators to the same frequency.  

   This internet draft is only about the first meaning, as QIRG via 
   [RFC9583] addresses only that meaning. Examples of the second 
   meaning are methods that use entangled photon pairs from physical 
   processes (e.g. spontaneous parametric down conversion), or that use 
   quantum interference of photons (Hong–Ou–Mandel effect). The second 
   meaning is out of scope of this internet draft. 

2. Quantum Clock Synchronization 

   [RFC9583], and references therein refer to [Jozsa2000] for "quantum 
   clock synchronisation". [Jozsa2000] introduces three methods for 
   synchronizing a pair of spatially separated clocks, Alice and Bob, 
   which are at rest in a common inertial frame. 

   1. Einstein Synchronization. This involves an operational line-of-
      sight exchange of light pulses between two Alice and Bob. This 
      method is based on the presumption that the speed of light, and 
      hence optical distance, is the same from Alice to Bob as vice 
      versa. 

   2. Eddington's Slow Clock Transport. In this scheme, Alice and Bob 
      are first synchronized locally, and then they are transported 
      adiabatically (infinitesimally slowly) to their final separate 
      locations. 



 
 
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   3. Quantum Clock Synchronization. This third method is quantum-
      entanglement based, in which Alice and Bob possess shared prior 
      entanglement. 

   Introduced as three different methods, the third would not rely on 
   either of the other two. In the third method, no actual clocks exist 
   initially but rather only "entangled clocks" in a global state which 
   does not evolve in time. The synchronized clocks are then extracted 
   via measurements and classical communications performed by Alice and 
   Bob, using the Ramsey method. More details are provided by 
   [Jozsa2000], as well as a critique by [Burt] on circular reasoning 
   by [Jozsa2000]. 

3. Matter-based entanglement requires slow clock transport 

   [Jozsa2000] assumes shared prior entanglement. The entanglement may 
   be matter-based, e.g. entanglement between pairs of atoms, ions or 
   electrons. That entanglement can only be achieved if those have been 
   close together in the past. As argued by [Burt], there the phase 
   information must be transported quantum mechanically and in such a 
   way that it avoids "classical" perturbations. That means slow clock 
   transport, which would make it a complicated variation of 
   Eddington's Slow Clock Transport. 

   Hence, we should exclude matter-based entanglement, and presume the 
   alternative. That is, entanglement between pairs of photons, the 
   units of electromagnetic radiation. 

4. Photon-based entanglement does not carry time information 

   [Jozsa2000] introduces their method as different from Einstein 
   Synchronization. That is, it does not rely on a bidirectional 
   channel with exactly equal delays in both directions. Figure 1 
   sketches the creation of shared prior entanglement between Alice and 
   Bob. The quantum channel is unidirectional: photons (photonic 
   qubits) travel from Alice to Bob. Those qubits are entangled with 
   qubits that stay with Alice. Alice and Bob have clocks that need to 
   be synchronized. Each of them has a clock output where the clock 
   information is consumed locally. Classical communication (not shown) 
   is used for asynchronous bidirectional exchange of information for 
   the quantum clock synchronization protocol. 






 
 
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   a)       +-------+          +-------+ 
            |       |          |       | 
            | Alice | -------> |  Bob  | 
            |       |          |       | 
            +-------+          +-------+ 
                |                  |     
                V                  V     
                                         
               Out                Out    
    
   b)       +-------+          +-------+ 
            |       |          |       | 
            | Alice | ---.T--> |  Burt | 
            |       |          |       | 
            +-------+          +-------+ 
                |                  |     
                V                  V     
                                         
               Out                Out    
    
    
           Figure 1 Effect of delay .T on clock synchronization. 
        (Showing only the quantum channel: from Alice to Bob & Burt) 

   The problem with this approach is that light (photons) do not carry 
   time information. If a classical pulse of light is sent from Alice 
   to Bob, and a similar classical pulse of light is sent from Alice to 
   Burt with a delay .T, then Burt will measure the same as Bob, just 
   .T later. This is true, independent of the number of photons in the 
   pulse, or whether the pulse is a single photonic qubit. 

   We conclude that if Alice synchronizes this way with both Bob and 
   Burt, that Burt's clock will be lagging .T behind Bob's clock. 

5. No known method can create the required initial conditions without 
   already synchronized clocks 

   For the algorithm by [Jozsa2000] to work, a shared measurement basis 
   is required between the two quantum systems. However, no practical 
   method is known to the authors which can create this without the use 
   of already synchronized clocks. The same argument was made by 
   [Burt], who argues that the initial paper boils down to circular 
   reasoning. 

   The only proposed option is to connect the local measurement bases 
   to e.g. absolute orientation in the universe. However, no methods 
   are known to achieve this, and it is suspected by the authors that 
 
 
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   the concept goes against the rule that absolute quantum phase is 
   irrelevant. 

6. Current synchronization solutions suffice 

   Our final question was why we don't see more work on quantum clock 
   synchronization by e.g. metrology institutes. We suspect that the 
   reason is economical, and that current clock synchronization 
   solutions based on the first method suffice. 

7. Security Considerations 

   Not applicable. The (in)validity of quantum clock synchronization 
   has no security considerations. 

8. IANA Considerations 

   Not applicable. The (in)validity of quantum clock synchronization 
   has no IANA considerations. 

9. Conclusions 

   We conclude that [RFC9583]-type quantum clock synchronization is not 
   a valid quantum-internet application. We have provided four 
   arguments for this. 

   o Matter-based entanglement requires slow clock transport. 

   o Photon-based entanglement does not carry time information. 

   o No known method can create the required initial conditions 
      without already synchronized clocks. 

   o Current synchronization solutions suffice. 

   These are relevant insights to those who use [RFC9583] as basis for 
   investments in quantum internet. 

10. Informative References 

   [RFC9583] Wang, C. "Application Scenarios for the Quantum Internet", 
             RFC 9583, June 2024, 
             https://datatracker.ietf.org/doc/rfc9583/ 




 
 
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   [Aquina]  Aquina, N, et al, "A Critical Analysis of Deployed Use 
             Cases for Quantum Key Distribution and Comparison with 
             Post-Quantum Cryptography", EPJ Quantum Technology, 
             Vol.12, No.1, 6 May 2025, 
             https://research.tue.nl/nl/publications/a-critical-
             analysis-of-deployed-use-cases-for-quantum-key-distrib-2/ 

   [Jozsa2000]   Jozsa, R, et al, "Quantum Clock Synchronization Based 
             on Shared Prior Entanglement", Phys. Rev. Lett. 85, 2010 – 
             Published 28 August, 2000, 
             https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.
             85.2010 

   [Burt]   Burt, E, et al, "Comment on 'Quantum Clock Synchronization 
             Based on Shared Prior Entanglement'", Phys. Rev. Lett. 87, 
             129801 (2001), 
             https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.
             87.12980. 

   [Ilo-Okeke] Ilo-Okeke, E.O., et al, "Remote quantum clock 
             synchronization without synchronized clocks", npj Quantum 
             Inf 4, 40 (2018), https://www.nature.com/articles/s41534-
             018-0090-2 

   [Komar] Kómár, P., et al, "A quantum network of clocks", DOI 
             10.1038/nphys3000, October 2013, 
             https://arxiv.org/pdf/1310.6045.pdf. 

   [Guo]   Guo, X., et al, "Distributed quantum sensing in a  
             continuous-variable entangled network", Nature Physics, 
             DOI 10.1038/s41567-019-0743-x, December 2019, 
             https://www.nature.com/articles/s41567-019-0743-x. 

11. Acknowledgments 

   This document was prepared using 2-Word-v2.0.template.dot. 










 
 
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Appendix A.                 Discussion of other references 

   In the appendix, we briefly discuss other references on quantum 
   clock synchronization. They don't change the conclusions of this 
   internet draft. 

A.1. [Ilo-Okeke] 

   [Ilo-Okeke] uses entanglement purification, a.k.a. entanglement 
   distillation, to improve the quality of the entanglement. It is 
   based on the same assumptions as [Jozsa2000]. 

A.2. [Komar] 

   [Komar] is cited by [RFC9583]. It presumes a perfect GHZ-state as a 
   starting point, similar to [Jozsa2000], which can only be achieved 
   in the presence of already synchronised clocks. 

A.3. [Guo] 

   [Guo] is cited by [RFC9583]. It references [Komar] for clock 
   synchronisation. 

    






















 
 
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Authors' Addresses 
   Oskar van Deventer 
   TNO 
   Anna van Buerenplein 1 
   2595 DA Den Haag 
   Netherlands 
      
   Email: oskar.vandeventer@tno.nl 
    
   Jesse Vogel 
   TNO 
   Anna van Buerenplein 1 
   2595 DA Den Haag 
   Netherlands 
      
   Email: jesse.vogel@tno.nl 
    
   Otmar Ubbens 
   TNO 
   Anna van Buerenplein 1 
   2595 DA Den Haag 
   Netherlands 
      
   Email: otmar.ubbens@tno.nl 
    
   Esteban Aguilera 
   TNO 
   Anna van Buerenplein 1 
   2595 DA Den Haag 
   Netherlands 
      
   Email: esteban.aguiler@tno.nl 


    
    































 
 
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