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
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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.
[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].
[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.
[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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