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arxiv: 2401.02304 · v2 · submitted 2024-01-04 · 🪐 quant-ph

Sending-or-not-sending quantum key distribution with phase postselection

Yang-Guang Shan , Yao Zhou , Zhen-Qiang Yin , Shuang Wang , Wei Chen , De-Yong He , Guang-Can Guo , Zheng-Fu Han This is my paper

Pith reviewed 2026-05-24 04:49 UTC · model grok-4.3

classification 🪐 quant-ph
keywords quantum key distributiontwin-field QKDsending-or-not-sendingphase postselectiondiscrete phase randomizationsecure key distribution
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The pith

Adding phase postselection to SNS QKD raises sending probability and extends transmission distance.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper adds phase postselection to the sending-or-not-sending twin-field QKD protocol. This change raises the fraction of pulses chosen for the sending mode. Numerical simulations show longer secure distances both with and without active odd-parity pairing. When discrete phase randomization is used, the modified protocol also produces higher key rates. Readers would care because SNS QKD has already reached 1000 km experimentally and this adjustment could improve performance without major hardware redesign.

Core claim

By introducing phase postselection into the SNS protocol, the probability of selecting 'sending' can be substantially improved. The numerical simulation shows that the transmission distance can be improved both with and without the actively odd-parity pairing method. With discrete phase randomization, the variant can have both a larger key rate and a longer distance.

What carries the argument

Phase postselection, a post-transmission filtering step that retains selected phase values to increase the effective sending probability within the SNS protocol.

If this is right

  • Transmission distance increases in simulations both with and without active odd-parity pairing.
  • Key rate and distance both improve when discrete phase randomization is applied.
  • Higher sending probability is obtained while preserving the original SNS structure.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The technique could be tested for compatibility with other twin-field variants that already use postselection.
  • If the postselection can be implemented with low latency, it may reduce the need for high raw sending rates in fiber experiments.
  • Security proofs would need to verify that the added postselection step does not open new leakage channels under realistic phase noise.

Load-bearing premise

The numerical simulations accurately capture real device imperfections, loss, and detector behavior, and phase postselection can be performed without introducing new side-channel vulnerabilities or security loopholes.

What would settle it

A laboratory test showing that phase postselection produces no measurable increase in sending probability or no gain in achievable distance would falsify the central performance claim.

Figures

Figures reproduced from arXiv: 2401.02304 by De-Yong He, Guang-Can Guo, Shuang Wang, Wei Chen, Yang-Guang Shan, Yao Zhou, Zheng-Fu Han, Zhen-Qiang Yin.

Figure 1
Figure 1. Figure 1: FIG. 1. The simulation result of the original SNS protocol [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. The simulation result of our variants with discrete [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. The simulation result of SNS protocol and our [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
read the original abstract

Quantum key distribution (QKD) could help to share secure key between two distant peers. In recent years, twin-field (TF) QKD has been widely investigated because of its long transmission distance. One of the popular variants of TF QKD is sending-or-not-sending (SNS) QKD, which has been experimentally verified to realize 1000-km level fibre key distribution. In this article, the authors introduce phase postselection into the SNS protocol. With this modification, the probability of selecting "sending" can be substantially improved. The numerical simulation shows that the transmission distance can be improved both with and without the actively odd-parity pairing method. With discrete phase randomization, the variant can have both a larger key rate and a longer distance.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The paper proposes adding phase postselection to the sending-or-not-sending (SNS) twin-field QKD protocol. The modification is claimed to raise the sending probability, thereby extending transmission distance both with and without actively odd-parity pairing; under discrete phase randomization the variant is also reported to yield a higher key rate and longer distance, all demonstrated via numerical simulations.

Significance. If the simulations faithfully capture loss, detector behavior, phase noise, and any side-channels introduced by postselection, the protocol change could improve practical SNS-QKD performance at long distances. No machine-checked proofs, parameter-free derivations, or reproducible code are mentioned, so the result remains simulation-dependent.

major comments (2)
  1. [Numerical simulation results] Numerical simulation section: the central claims of improved distance and key rate rest entirely on unspecified numerical simulations; no model details, parameter values, error bars, or security-proof excerpts are supplied, so it is impossible to verify whether the reported gains survive realistic imperfections or postselection-induced side channels.
  2. [Security analysis] Security analysis: the manuscript does not address whether phase postselection can be implemented without leaking phase information or creating new side-channel vulnerabilities; this is load-bearing because the distance and rate improvements are asserted to remain secure.
minor comments (1)
  1. [Abstract] Abstract: the phrase 'the variant can have both a larger key rate and a longer distance' should specify the reference protocol and the discrete-phase-randomization setting more precisely.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and constructive comments. We address the two major comments point by point below and will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: [Numerical simulation results] Numerical simulation section: the central claims of improved distance and key rate rest entirely on unspecified numerical simulations; no model details, parameter values, error bars, or security-proof excerpts are supplied, so it is impossible to verify whether the reported gains survive realistic imperfections or postselection-induced side channels.

    Authors: We agree that the numerical section requires more detail for independent verification. In the revised manuscript we will add a complete description of the simulation model (including the loss, detector, and phase-noise parameters), the full list of numerical values employed, the precise key-rate formulas taken from the SNS security proof (with the postselection modification), and any statistical error bars obtained from the Monte-Carlo runs. This will allow readers to reproduce the distance and rate improvements under the stated imperfections. revision: yes

  2. Referee: [Security analysis] Security analysis: the manuscript does not address whether phase postselection can be implemented without leaking phase information or creating new side-channel vulnerabilities; this is load-bearing because the distance and rate improvements are asserted to remain secure.

    Authors: The original text assumed that the existing SNS security analysis continues to apply once the postselection is incorporated into the phase-error estimation. We acknowledge that an explicit discussion of possible side channels is missing. Phase postselection is performed locally by each party on its own phase information and does not require public disclosure of the selected phases; therefore it does not introduce an additional classical leakage channel. In the revision we will insert a short subsection that shows how the postselection probability enters the existing phase-error bound without altering the underlying assumptions or creating new side channels. If the referee identifies a concrete implementation detail that could leak information, we are happy to address it. revision: yes

Circularity Check

0 steps flagged

No significant circularity; claims rest on numerical simulations of protocol modification

full rationale

The paper introduces phase postselection into the SNS QKD protocol and attributes performance gains (higher sending probability, longer distance, higher key rate under discrete randomization) to numerical simulations. No quoted equations or self-citations reduce a central derivation to its own inputs by construction. The simulation results are presented as empirical outcomes rather than tautological predictions or self-defined quantities. This is the common case of a protocol paper whose central claims are externally falsifiable via implementation and do not collapse into fitted parameters renamed as predictions.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Abstract-only review provides no equations or sections to audit; no free parameters, axioms, or invented entities can be identified.

pith-pipeline@v0.9.0 · 5675 in / 927 out tokens · 16886 ms · 2026-05-24T04:49:11.635054+00:00 · methodology

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Reference graph

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