QKD: Add more text on loss mechanisms
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2 changed files with 139 additions and 11 deletions
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@ -437,6 +437,7 @@ various aspects of currents in superconducters as well as phonons\cite{berriosHi
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\todoplaceholder{Something is missing here.}
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\subsection{Practical Challenges}
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The central challenge in general quantum computers is extending the lifetime of the quantum state encoding a qubit.
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Quantum states are extremely sensitive to disturbances, and despite the best efforts to shield them against external
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influence, their lifetime is still inconveniently short compared to the timescales required for quantum computation,
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@ -492,27 +493,65 @@ concern of photon number splitting attacks and because of decoherence\footnote{
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could increase the quantum state's photon number, adding entangled photons that share the original quantum state.
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Alas, doing this would not gain us much in a QKD system because an interaction of any of the quantum state's photons
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with the fiber---that is, the same loss as before---would disturb the entire entangled state.
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}, and thus the system's bit rate decreases exponentially with distance due to absorption. Some QKD systems can reach
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}, and thus the system's bit rate decreases exponentially with distance due to attenuation. Some QKD systems can reach
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ranges of several hundred kilometers, but the resulting payload data rate---usually called \emph{secret key rate}---of
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these long distance systems is measured in kilobits per second.
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\subsection{Loss in optical fibers}
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When transmitted over a fiber, there are multiple effects that degrade the quantum-optical signal of a QKD system, which
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are collectively referred to as \emph{loss}. We can coarsely classify these degrading effects into two categories:
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\emph{Decoherence}, and \emph{Absorption}. Decoherence effects result in the quantum state being changed in transit,
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\emph{decoherence}, and \emph{attenuation}. Decoherence effects result in the quantum state being changed in transit,
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which depending on the QKD implementation may mean destroying information contained within the state such as by
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disturbing the pulse's polarization, or destruction of entanglement between the in-flight state and another local state.
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In an optical channel affected by such decoherence effects, a quantum state enters the channel, and subsequently exits
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it at the other end changed. In contrast, absorption means the quantum state is not ever leaving the channel.
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In contrast, attenuation means the quantum state is not ever leaving the channel.
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In practice, absorption limits the length of an individual fiber run, as it becomes problematic at short distances.
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Decoherence is less relevant for the distance limitation, and mostly limits which fiber-optic technologies can be
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In practice, attenuation is the primary factor limiting the length of an individual fiber run in QKD. Even modern,
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ultra-low loss optical fiber has an attenuation in the order of \qty{0.15}{\decibel\per\kilo\meter}, resulting in a loss
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of half the signal's power, equivalent to half of all QKD pulses, in just \qty{20}{\kilo\meter}. For longer reaches,
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these losses ar multiplicative, so after only \qty{200}{\kilo\meter} only one in a thousand single-photon pulses entering
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the fiber will exit it at the other end \cite{chesnoyUnderseaFiberCommunication2015}.
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Decoherence effects are less relevant for the distance limitation, and mostly limit which fiber-optic technologies can be
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utilized in the first place. Due to decoherence, QKD systems usually use Single-Mode (SM) fiber over Multi-Mode (MM)
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fiber, and decoherence makes it more difficult to utilize Wavelength Division Multiplexing (xWDM) to send multiple
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either quantum or classical optical signals through a single fiber. \todo{go more into the details on xWDM, elaborate on
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decoherence mechanisms, especially crosstalk in the context of
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xWDM.}
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either quantum or classical optical signals through a single fiber.
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\todo{CV-QKD}
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Attenuation in optical fibers has a number of origins. The main factor is scattering of photons on the fiber core, with
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absorbtion due to interactions between photons and the fiber core's molecular structure or embedded contaminants only
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playing a minor role. The primary component of scattering is fluctuations in the fiber core's molecular structure, with
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scattering on phonons (Brillouin scattering) or photons (Raman scattering) only adding a samll amount of
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loss\cite{wandelAttenuationSilicabasedOptical2006}.
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Like attenuation, decoherence can also result from a number of different mechanisms. Two optically \emph{linear}
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mechanisms, i.e.\ ones that do not depend on incident signal power, are chromatic dispersion and polarization mode
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dispersion (PMD). PMD disturbs the signal's polarization. PMD strongly depends on wavelength and is highly sensitive to
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environmental factors such as temperature or vibration \cite{brodskyPolarizationModeDispersion2006}. QKD systems
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frequently use polarization-based encodings, which are sensitive to PMD. PMD is usually mitigated by continuously
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measuring the fiber's end-to-end PMD, and adjusting a polarization controller placed
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in-line\cite{wangLongdistanceCopropagationQuantum2017, ImpactPolarizationMode,
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agnesiAllfiberSelfcompensatingPolarization2019} with the fiber to cancel out the fiber's PMD.
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Chromatic dispersion arises from the fiber's materials' refractive index not being perfectly constant across
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the spectral bandwidth of the optical signal, leading some frequency components of the signal to traverse the fiber
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faster than others, resulting in pulses being spread out as they continue along the fiber. Chromatic dispersion is a
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concern in some long-distance QKD systems that need to operate at a timing precision down to a few dozen picoseconds,
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but like PMD it can be compensated at the endpoint \cite{neumannExperimentallyOptimizingQKD2021,
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kiselevAnalysisChromaticDispersion2020}.
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Nonlinear effects such as the AC Kerr Effect, Stimulated Raman Scattering as well as Stimulated Brillouin Scattering
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can produce intermodulation when a quantum optical signal is sent through the same fiber as another, much brighter
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classical optical signal. These nonlinear effects are relevant for QKD systems that either send a reference clock
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through the same fiber as the QKD pulses, or that aim for coexistence between QKD pulses and classical optical
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networking on the same fiber, for instance in an in xWDM setup.
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In the AC Kerr effect, a strong optical signal influences the refractive indes of the fiber core, which modulates other
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signals propagating through the same fiber. Stimualated Brillouin Scattering arises when a high-power incident signal
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causes the emission of phonons inside the fiber core, which then act as a source of Brillouin scattering to weaker
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signals\cite{chesnoyUnderseaFiberCommunication2015}. Stimulated Raman Scattering is similar, only that the QKD signal is
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affected by direct Raman scattering on the stronger signal's photons.
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\todo{Some detail on CV-QKD}
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\subsection{Relaying}
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\todo{(one?) term of the art seems to be "repeater"}
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91
main.bib
91
main.bib
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@ -15,6 +15,26 @@
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file = {/home/jaseg/Zotero/storage/7C2Z5Y9P/Adhikari et al. - 2022 - Don't Look Up Ubiquitous Data Exfiltration Pathwa.pdf}
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}
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@article{agnesiAllfiberSelfcompensatingPolarization2019,
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title = {All-Fiber Self-Compensating Polarization Encoder for Quantum Key Distribution},
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author = {Agnesi, Costantino and Avesani, Marco and Stanco, Andrea and Villoresi, Paolo and Vallone, Giuseppe},
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date = {2019-05-15},
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journaltitle = {Optics Letters},
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shortjournal = {Opt. Lett., OL},
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volume = {44},
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number = {10},
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pages = {2398--2401},
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publisher = {Optica Publishing Group},
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issn = {1539-4794},
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doi = {10.1364/OL.44.002398},
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url = {https://opg.optica.org/ol/abstract.cfm?uri=ol-44-10-2398},
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urldate = {2024-09-04},
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abstract = {Quantum key distribution (QKD) allows distant parties to exchange cryptographic keys with unconditional security by encoding information on the degrees of freedom of photons. Polarization encoding has been extensively used for QKD along free-space, optical fiber, and satellite links. However, the polarization encoders used in such implementations are unstable, expensive, and complex and can even exhibit side channels that undermine the security of the protocol. Here we propose a self-compensating polarization encoder based on a lithium niobate phase modulator inside a Sagnac interferometer and implement it using only commercial off-the-shelf (COTS) components. Our polarization encoder combines a simple design and high stability reaching an intrinsic quantum bit error rate as low as 0.2\%. Since realization is possible from the 800 to the 1550\&\#x00A0;nm band using COTS devices, our polarization modulator is a promising solution for free-space, fiber, and satellite-based QKD.},
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langid = {english},
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keywords = {Lithium niobate,Optical delay lines,Optical fibers,Polarization mode dispersion,Quantum key distribution,Single-photon avalanche diodes},
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file = {/home/jaseg/Sync/Research/Zotero/2019_Agnesi et al_All-fiber self-compensating polarization encoder for quantum key distribution.pdf}
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}
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@article{albertiniHowAbuseFix,
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title = {How to {{Abuse}} and {{Fix Authenticated Encryption Without Key Commitment}}},
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author = {Albertini, Ange and Duong, Thai and Gueron, Shay and Kölbl, Stefan and Luykx, Atul and Schmieg, Sophie},
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@ -547,6 +567,24 @@
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file = {/home/jaseg/Sync/Research/Zotero/2022_Braun et al_MOTION – A Framework for Mixed-Protocol Multi-Party Computation.pdf}
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}
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@article{brodskyPolarizationModeDispersion2006,
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title = {Polarization {{Mode Dispersion}} of {{Installed Fibers}}},
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author = {Brodsky, Misha and Frigo, Nicholas J. and Boroditsky, Misha and Tur, Moshe},
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date = {2006-12},
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journaltitle = {Journal of Lightwave Technology},
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volume = {24},
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number = {12},
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pages = {4584--4599},
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issn = {1558-2213},
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doi = {10.1109/JLT.2006.885781},
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url = {https://ieeexplore.ieee.org/document/4063384/?arnumber=4063384&tag=1},
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urldate = {2024-09-04},
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abstract = {Polarization mode dispersion (PMD), a potentially limiting impairment in high-speed long-distance fiber-optic communication systems, refers to the distortion of propagating optical pulses due to random birefringences in an optical system. Because these perturbations (which can be introduced through manufacturing imperfections, cabling stresses, installation procedures, and environmental sensitivities of fiber and other in-line components) are unknowable and continually changing, PMD is unique among optical impairments. This makes PMD both a fascinating research subject and potentially one of the most challenging technical obstacles for future optoelectronic transmission. Mitigation and compensation techniques, proper emulation, and accurate prediction of PMD-induced outage probabilities critically depend on the understanding and modeling of the statistics of PMD in installed links. Using extensive data on buried fibers used in long-haul high-speed links, the authors discuss the proposition that most of the temporal PMD changes that are observed in installed routes arise primarily from a relatively small number of "hot spots" along the route that are exposed to the ambient environment, whereas the buried shielded sections remain largely stable for month-long time periods. It follows that the temporal variations of the differential group delay for any given channel constitute a distinct statistical distribution with its own channel-specific mean value. The impact of these observations on outage statistics is analyzed, and the implications for future optoelectronic fiber-based transmission are discussed},
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eventtitle = {Journal of {{Lightwave Technology}}},
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keywords = {Communication systems,High speed optical techniques,Optical distortion,Optical fiber cables,optical fiber communication,Optical fiber communication,optical fiber dispersion,optical fiber polarization,Optical fiber polarization,Optical propagation,Optical pulses,Optical sensors,Polarization mode dispersion,Statistical distributions},
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file = {/home/jaseg/Sync/Research/Zotero/2006_Brodsky et al_Polarization Mode Dispersion of Installed Fibers.pdf;/home/jaseg/Zotero/storage/CAAVGKF5/4063384.html}
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}
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@online{byPCBsLinearMotors2018,
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title = {{{PCBs As Linear Motors}}},
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author = {By},
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@ -709,7 +747,7 @@
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@book{chesnoyUnderseaFiberCommunication2015,
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title = {Undersea Fiber Communication Systems},
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author = {Chesnoy, José and Chesnoy, José},
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author = {Chesnoy, José},
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date = {2015},
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edition = {Second edition},
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publisher = {Academic Press},
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@ -1604,6 +1642,13 @@
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file = {/home/jaseg/Zotero/storage/U6BHG3AD/stamp.html}
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}
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@online{ImpactPolarizationMode,
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title = {Impact of Polarization Mode Dispersion on Entangled Photon Distribution},
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url = {https://arxiv.org/html/2408.01754v1},
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urldate = {2024-09-04},
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file = {/home/jaseg/Zotero/storage/XVM7CYB5/2408.html}
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}
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@inproceedings{impagliazzoPersonalViewAveragecase1995,
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title = {A Personal View of Average-Case Complexity},
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booktitle = {Proceedings of {{Structure}} in {{Complexity Theory}}. {{Tenth Annual IEEE Conference}}},
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@ -2640,6 +2685,24 @@
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file = {/home/jaseg/Zotero/storage/MNTNWQW4/Nelson and Askarov - 2022 - With a Little Help from My Friends Transport Deni.pdf}
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}
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@article{neumannExperimentallyOptimizingQKD2021,
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title = {Experimentally Optimizing {{QKD}} Rates via Nonlocal Dispersion Compensation},
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author = {Neumann, Sebastian Philipp and Ribezzo, Domenico and Bohmann, Martin and Ursin, Rupert},
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date = {2021-04-01},
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journaltitle = {Quantum Science and Technology},
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shortjournal = {Quantum Sci. Technol.},
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volume = {6},
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number = {2},
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pages = {025017},
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issn = {2058-9565},
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doi = {10.1088/2058-9565/abe5ee},
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url = {https://iopscience.iop.org/article/10.1088/2058-9565/abe5ee},
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urldate = {2024-09-04},
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abstract = {Quantum key distribution (QKD) enables unconditionally secure communication guaranteed by the laws of physics. The last decades have seen tremendous efforts in making this technology feasible under real-life conditions, with implementations bridging ever longer distances and creating ever higher secure key rates. Readily deployed glass fiber connections are a natural choice for distributing the single photons necessary for QKD both in intra- and intercity links. Any fiber-based implementation however experiences chromatic dispersion which deteriorates temporal detection precision. This ultimately limits maximum distance and achievable key rate of such QKD systems. In this work, we address this limitation to both maximum distance and key rate and present an effective and easy-to-implement method to overcome chromatic dispersion effects. By exploiting entangled photons’ frequency correlations, we make use of nonlocal dispersion compensation to improve the photons’ temporal correlations. Our experiment is the first implementation utilizing the inherently quantum-mechanical effect of nonlocal dispersion compensation for QKD in this way. We experimentally show an increase in key rate from 6.1 to 228.3 bits/s over 6.46 km of telecom fiber. Our approach is extendable to arbitrary fiber lengths and dispersion values, resulting in substantially increased key rates and even enabling QKD in the first place where strong dispersion would otherwise frustrate key extraction at all.},
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langid = {english},
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file = {/home/jaseg/Zotero/storage/CZZS49B2/Neumann et al. - 2021 - Experimentally optimizing QKD rates via nonlocal d.pdf}
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}
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@online{NewCompanyBuilds,
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title = {New Company Builds and Operates a Trans-{{Pacific}} Submarine Cable System between the {{US}} and {{Japan}} | {{Press Release}} | {{NTT}}},
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url = {https://group.ntt/en/newsrelease/2022/07/12/220712a.html},
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@ -3532,6 +3595,15 @@
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file = {/home/jaseg/Zotero/storage/2HCQ4S6I/Vu et al. - 2020 - Design and Performance of Relay-Assisted Satellite.pdf}
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}
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@thesis{wandelAttenuationSilicabasedOptical2006,
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title = {Attenuation in Silica-Based Optical Fibers},
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author = {Wandel, Marie Emilie},
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date = {2006},
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institution = {Technical University of Denmark},
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langid = {english},
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file = {/home/jaseg/Zotero/storage/LXMAVLMC/Wandel - Attenuation in silica-based optical fibers.pdf}
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}
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@article{wangBeatingPhotonNumberSplittingAttack2005,
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title = {Beating the {{Photon-Number-Splitting Attack}} in {{Practical Quantum Cryptography}}},
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author = {Wang, Xiang-Bin},
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@ -3627,6 +3699,23 @@
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langid = {english}
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}
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@article{wangLongdistanceCopropagationQuantum2017,
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title = {Long-Distance Copropagation of Quantum Key Distribution and Terabit Classical Optical Data Channels},
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author = {Wang, Liu-Jun and Zou, Kai-Heng and Sun, Wei and Mao, Yingqiu and Zhu, Yi-Xiao and Yin, Hua-Lei and Chen, Qing and Zhao, Yong and Zhang, Fan and Chen, Teng-Yun and Pan, Jian-Wei},
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date = {2017-01-03},
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journaltitle = {Physical Review A},
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shortjournal = {Phys. Rev. A},
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volume = {95},
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number = {1},
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pages = {012301},
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issn = {2469-9926, 2469-9934},
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doi = {10.1103/PhysRevA.95.012301},
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url = {https://link.aps.org/doi/10.1103/PhysRevA.95.012301},
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urldate = {2024-09-04},
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langid = {english},
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file = {/home/jaseg/Zotero/storage/CMWK7SHH/Wang et al. - 2017 - Long-distance copropagation of quantum key distrib.pdf}
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}
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@article{wangTopologicalOptimizationHybrid2020,
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title = {Topological Optimization of Hybrid Quantum Key Distribution Networks},
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author = {Wang, Yaxing and Li, Qiong and Mao, Haokun and Han, Qi and Huang, Furong and Xu, Hongwei},
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