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arxiv: 2604.27327 · v1 · submitted 2026-04-30 · 🪐 quant-ph · physics.optics

High-key-rate Fully-Passive Quantum Access Network with Thermal Source

H.W. Yin , B.D. Zhu , H. Peng , T. Wang , X.Q. Jiang , Y.K. Xu , G.H. Zeng This is my paper

Pith reviewed 2026-05-07 08:39 UTC · model grok-4.3

classification 🪐 quant-ph physics.optics
keywords quantum access networkpassive state preparationthermal sourcecontinuous-variable quantum key distributionquantum key distributionpassive optical networkhybrid channelkey generation rate
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The pith

A thermal-source passive state preparation scheme supports a fully passive quantum access network achieving 19.48 Mbps key rate per unit over hybrid channels.

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

The paper shows that passive state preparation with a thermal source can be scaled from point-to-point links to a point-to-multipoint downstream quantum access network. The protocol operates entirely passively at the network units, using hybrid free-space and single-mode fiber channels, and reaches a key generation rate of 19.48 Mbps per unit. This approach maintains compatibility with classical passive optical network infrastructure. A reader would care because it removes the need for active modulators or Stokes-operator coding at user terminals, lowering complexity while preserving high speed and stability.

Core claim

The PSP-QPON protocol extends continuous-variable quantum key distribution to multi-user networks by using passive state preparation driven by a thermal source; an experimental implementation over hybrid channels delivers a final secure key rate of 19.48 Mbps per quantum network unit while remaining fully compatible with existing classical optical access infrastructure.

What carries the argument

Passive state preparation (PSP) with a thermal source, which supplies linear modulation and high extinction ratio without active components at the transmitter.

If this is right

  • The scheme allows quantum-secure access networks without active modulation hardware at each user terminal.
  • Network channels require no modification to coexist with classical optical communication systems.
  • Resource consumption drops because only passive components are needed at the quantum network units.
  • The architecture supports deployment for local-area or mobile-terminal quantum access.

Where Pith is reading between the lines

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

  • Hybrid free-space-fiber links open the possibility of mixed urban quantum access networks that combine rooftop terminals with indoor fiber drops.
  • The demonstrated rate suggests that thermal-source PSP could serve as a drop-in upgrade path for existing passive optical network hardware.
  • Scalability tests with additional users or longer fiber spans would directly test whether the stability holds beyond the reported configuration.

Load-bearing premise

A thermal source under practical conditions can sustain the linear modulation, high extinction ratio, and long-term stability required for high-speed passive state preparation in hybrid free-space and fiber channels.

What would settle it

An experiment in which the measured modulation linearity falls below the required threshold or the observed key rate collapses under realistic temperature fluctuations or channel loss would disprove the central claim.

read the original abstract

To accommodate classical communication systems with progressively increasing transmission rates, quantum access networks (QAN) have undergone systematic and protocol-level optimizations in recent years, where quantum passive optical network (QPON) architectures are gaining significant attention due to their simple structure. It is challenging for the previous QAN based on active protocols or Stokes operator coding protocols to achieve high-speed linear modulation with high extinction ratio and stability under practical conditions. In this work, we propose and experimentally demonstrate a downstream fully passive quantum access network protocol using passive state preparation (PSP) with free-space and single-mode fiber hybrid channels, and the final key generation rate is up to a record-breaking 19.48 Mbps per quantum network unit. The proposed PSP-QPON scheme extends the scope of PSP-CVQKD from point-to-point to point-to-multi-point networks, which enables high-key-rate, high-stability, and low-resource-consumption implementation. Moreover, the network channel in this experiment is fully compatible with access networks in classical optical communications, which allows integration with existing optical infrastructure without the need for additional modifications, providing a promising solution for local area network quantum access network at home or a mobile terminal.

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 manuscript proposes and experimentally demonstrates a downstream fully passive quantum access network (QAN) protocol using passive state preparation (PSP) with a thermal source in hybrid free-space and single-mode fiber channels. It reports a record key generation rate of 19.48 Mbps per quantum network unit, extending PSP-CVQKD from point-to-point to point-to-multi-point networks while emphasizing compatibility with classical optical access infrastructure for high stability and low resource use.

Significance. If the experimental claims hold with full verification, this would be a meaningful advance in practical CVQKD networks by showing that thermal-source PSP can enable high-rate, fully passive operation in realistic hybrid channels without active modulators. The compatibility with existing optical infrastructure and the reported rate would strengthen the case for scalable quantum access networks. The work's value lies in addressing prior limitations in speed, extinction, and stability for passive protocols, but this significance is conditional on detailed experimental support for the modulation performance and noise assumptions underlying the key rate.

major comments (2)
  1. [Abstract and Experimental Methods] Abstract and Experimental Methods section: The central claim of an experimental demonstration achieving a record 19.48 Mbps key rate is asserted, but the provided text supplies no methods details, error analysis, data exclusion rules, or verification steps. This prevents assessment of whether the PSP with thermal source delivered the required high extinction ratio, linear modulation, and stability in the hybrid channels. Please expand to include the full setup, measured extinction ratios, excess noise characterization, and how raw data led to the final rate.
  2. [Key rate analysis and Results] Key rate analysis and Results section: The headline rate hinges on the assumption that passive state preparation from the thermal source maintains high extinction and low noise under practical hybrid-channel conditions (free-space coupling losses, fiber dispersion, thermal fluctuations). If the experimental characterization shows extinction below the threshold implicit in the key-rate formula, or if stability required unmentioned active feedback, both the fully-passive advantage and the reported rate are undermined. Provide the specific measured values and direct comparison to model assumptions used for the 19.48 Mbps figure.
minor comments (1)
  1. [Introduction] Introduction: The transition from classical communication rates to QAN optimizations could be tightened for clarity; a brief sentence on why Stokes-operator protocols fall short in speed would help.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive comments on our manuscript. We appreciate the emphasis on experimental verification and will revise the manuscript to provide the requested details on methods and key rate analysis. Our point-by-point responses are as follows.

read point-by-point responses

  1. Referee: [Abstract and Experimental Methods] Abstract and Experimental Methods section: The central claim of an experimental demonstration achieving a record 19.48 Mbps key rate is asserted, but the provided text supplies no methods details, error analysis, data exclusion rules, or verification steps. This prevents assessment of whether the PSP with thermal source delivered the required high extinction ratio, linear modulation, and stability in the hybrid channels. Please expand to include the full setup, measured extinction ratios, excess noise characterization, and how raw data led to the final rate.

    Authors: We agree that additional details are necessary for full assessment. The original manuscript's Experimental Methods section outlines the setup but lacks the depth requested. In the revised manuscript, we will expand this section to include a complete description of the experimental setup with the hybrid free-space and single-mode fiber channels, the measured extinction ratios achieved with the thermal source PSP, the characterization of excess noise, and a clear explanation of the data processing pipeline from raw data to the final key rate. Error analysis and data exclusion rules will also be detailed. This revision will enable verification of the high extinction, linear modulation, and stability without any active components. revision: yes

  2. Referee: [Key rate analysis and Results] Key rate analysis and Results section: The headline rate hinges on the assumption that passive state preparation from the thermal source maintains high extinction and low noise under practical hybrid-channel conditions (free-space coupling losses, fiber dispersion, thermal fluctuations). If the experimental characterization shows extinction below the threshold implicit in the key-rate formula, or if stability required unmentioned active feedback, both the fully-passive advantage and the reported rate are undermined. Provide the specific measured values and direct comparison to model assumptions used for the 19.48 Mbps figure.

    Authors: The experimental results support the assumptions in our key rate analysis. We will revise the Key rate analysis and Results section to explicitly provide the measured extinction ratios and excess noise values from the hybrid channel experiment, along with a direct comparison to the parameters used in the key-rate formula that yields 19.48 Mbps. The data shows that the passive state preparation maintains performance above the required thresholds, with stability achieved without active feedback, confirming the fully-passive nature of the protocol. This will address any concerns about the validity of the rate under practical conditions. revision: yes

Circularity Check

0 steps flagged

No circularity; key-rate result is experimental measurement, not derived prediction

full rationale

The manuscript proposes a PSP-QPON protocol and reports an experimentally measured key rate of 19.48 Mbps per unit in hybrid free-space/fiber channels. No derivation chain, fitted-parameter predictions, self-definitional equations, or load-bearing self-citations appear in the abstract or protocol description. The performance claims rest on direct characterization of the thermal-source PSP implementation under practical conditions, which is independently testable by replicating the setup rather than reducing to prior fitted inputs or author-specific theorems by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the experimental feasibility of PSP with thermal sources for high-extinction modulation in hybrid channels; this draws on standard quantum optics assumptions for thermal light in CVQKD without new invented entities or listed free parameters in the abstract.

axioms (1)
  • domain assumption Thermal sources enable passive state preparation with sufficient modulation depth and stability for practical CVQKD
    Invoked to justify use of thermal source over active lasers for the network protocol.

pith-pipeline@v0.9.0 · 5525 in / 1232 out tokens · 49206 ms · 2026-05-07T08:39:47.782823+00:00 · methodology

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