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arxiv: 2606.25037 · v1 · pith:JPFGW3QSnew · submitted 2026-06-23 · 🪐 quant-ph

Arbitrarily Loss-Tolerant Quantum Position Verification in a Single Execution

Lloren\c{c} Escol\`a-Farr\`as , Boris \v{S}kori\'c , Florian Speelman This is my paper

Pith reviewed 2026-06-25 23:41 UTC · model grok-4.3

classification 🪐 quant-ph
keywords quantum position verificationloss tolerancesingle-shot protocolBB84no-signalling correlationsentangled adversariescommitment schemephoton loss
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The pith

A no-signalling lift of commitment techniques yields the first single-execution quantum position verification protocol that tolerates arbitrary photon loss while keeping exponential security against entangled attackers.

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

The paper shows how to adapt a commitment modification, previously limited to sequential repetitions, so that it works in a single parallel execution of a BB84-based quantum position verification protocol. The key step uses no-signalling correlations to prevent new attack vectors when the prover's responses are sent simultaneously. With a threshold k on the number of qubits that must be successfully committed, the probability that an entangled attacker is accepted falls exponentially in k. The protocol stays secure against bounded-entanglement adversaries, tolerates noise up to 3.7 percent, and works even when quantum communication is arbitrarily slow, thereby removing the distance barrier that loss imposed on earlier single-shot schemes.

Core claim

By utilizing different techniques based on no-signalling correlations, the commitment modification is lifted to the parallel regime while preserving the security guarantees of the underlying QPV protocol. Applying this to a BB84-based QPV protocol suitable for near-term implementation and secure against bounded-entanglement adversaries, fixing a threshold k on the number of successfully committed qubits yields an adversarial acceptance probability that decays exponentially in k. The resulting protocol maintains robustness to noise levels of up to 3.7% and remains secure under arbitrarily slow quantum communication.

What carries the argument

The commitment-based modification lifted from sequential to parallel execution via no-signalling correlations, applied to a BB84 QPV protocol with a threshold k on successful commitments.

If this is right

  • Adversarial acceptance probability decays exponentially in the threshold k.
  • The protocol tolerates arbitrary photon loss in one execution while retaining security.
  • Security holds against entangled attackers even when quantum messages travel arbitrarily slowly.
  • The same technique yields improved quantitative parameters when re-applied to sequential protocols.
  • QPV becomes feasible over arbitrary distances without requiring multiple rounds.

Where Pith is reading between the lines

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

  • The no-signalling lifting technique may apply to other quantum cryptographic tasks that combine commitments with parallel message exchange.
  • Moderate values of k could already deliver practical security levels in laboratory settings with current single-photon sources.
  • The 3.7 percent noise tolerance sets a concrete benchmark that future experiments can target or exceed.
  • The exponential decay suggests that security margins improve predictably with hardware improvements that raise the effective k.

Load-bearing premise

No-signalling correlations suffice to lift the commitment modification to parallel execution without creating new attack strategies or weakening the original BB84 security against bounded-entanglement adversaries.

What would settle it

An explicit entangled attack strategy on the parallel committed protocol whose acceptance probability fails to decay exponentially with the threshold k.

Figures

Figures reproduced from arXiv: 2606.25037 by Boris \v{S}kori\'c, Florian Speelman, Lloren\c{c} Escol\`a-Farr\`as.

Figure 1
Figure 1. Figure 1: Description of the QPVf∶n→m BB84 protocol. In [EFS25], it was shown that for a suitable class of functions f (see (8)), the protocol is secure against adversaries in the BE(O(n)) model, i.e., adversaries pre-sharing a number of entangled qubits linear in the size of the classical information. We now describe some structural properties of the function f that are relevant for the security analysis. The funct… view at source ↗
Figure 2
Figure 2. Figure 2: Schematic representation of QPVf∶n→m BB84 . may be substantial over long distances. As discussed in the introduction, this creates a fundamental vulnerability: an adversary can measure each incoming qubit in a randomly chosen basis and only report outcomes for those qubits for which the guess was correct, declaring loss otherwise. Since the adversary succeeds with probability 1/2 on each qubit, any protoco… view at source ↗
Figure 3
Figure 3. Figure 3: Description of the c-QPVf∶n→m BB84 protocol 4 Security Analysis of c-QPVf∶n→m BB84 As is customary in the literature, we consider the purified version of c-QPVf∶n→m BB84 , which is equiva￾lent to the original protocol. In this formulation, V0 prepares m EPR pairs ∣Φ + ⟩V1Q1⊗⋯⊗∣Φ + ⟩VmQm, and sends the qubit registers Q1, . . . , Qm to the prover. At a later stage, V0 measures the local registers V1 . . . V… view at source ↗
Figure 4
Figure 4. Figure 4: Schematic representation of c-QPVf∶n→m BB84 . Unlike [PITH_FULL_IMAGE:figures/full_fig_p008_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Schematic representation of a general attack on [PITH_FULL_IMAGE:figures/full_fig_p009_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Description of the (c-QPVf BB84) m protocol Similarly to c-QPVf∶n→m BB84 in Section 4, we analyze the security of c-QPVf BB84 via its purified formulation. In each round i, the verifiers prepare an EPR pair ∣Φ + ⟩V Q and send the register Q to 13 [PITH_FULL_IMAGE:figures/full_fig_p013_6.png] view at source ↗
read the original abstract

Quantum position verification (QPV) seeks to certify the spatial location of an untrusted prover, but is challenged fundamentally by entanglement-based attacks and experimentally by photon loss. Both issues were addressed separately in different works and were simultaneously resolved for sequentially repeated protocols in \textit{Phys.\ Rev.\ Lett.}\ \textbf{135},~260801 via a commitment-based modification that renders security independent of transmission losses. However, single-execution protocols are preferable in practice, and the original techniques do not extend to the parallel setting due to their reliance on sequential structure. We overcome this by utilizing different techniques based on no-signalling correlations, lifting the commitment modification to the parallel regime while preserving the security guarantees of the underlying QPV protocol. Applying this to a BB84-based QPV protocol suitable for near-term implementation and secure against bounded-entanglement adversaries, we prove that fixing a threshold~$k$ on the number of successfully committed qubits yields an adversarial acceptance probability that decays exponentially in~$k$. The resulting protocol maintains robustness to noise levels of up to~$3.7\%$ and remains secure under arbitrarily slow quantum communication, as does the original protocol. This yields the first fully loss-tolerant single-shot QPV protocol secure against entangled attackers, making QPV feasible over arbitrary distances. Finally, we refine the sequential analysis and obtain improved quantitative parameters for experimental implementations.

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

1 major / 2 minor

Summary. The paper claims to develop a technique using no-signalling correlations to adapt a commitment-based modification for loss-tolerance in quantum position verification (QPV) from sequential to parallel (single-execution) settings. Applied to a BB84 QPV protocol secure against bounded-entanglement adversaries, it establishes that imposing a threshold k on the number of successfully committed qubits results in an adversarial acceptance probability that decays exponentially with k. The protocol is shown to tolerate up to 3.7% noise and remain secure even with arbitrarily slow quantum communication, providing the first fully loss-tolerant single-shot QPV protocol secure against entangled attackers. Additionally, the sequential analysis is refined for improved parameters.

Significance. If the central claims hold, this work represents a significant advance in making QPV practical for arbitrary distances by resolving both entanglement attacks and photon loss in a single execution. The explicit exponential security bound and noise tolerance threshold are particularly valuable for experimental implementations. The refinement of the sequential protocol parameters also contributes to the field by improving quantitative bounds for near-term setups. The use of no-signalling to lift the security argument is a novel technical contribution.

major comments (1)
  1. [Section 3] Section 3 (No-Signalling Lift to Parallel Regime): The argument that no-signalling correlations suffice to extend the commitment security from sequential to parallel execution without introducing new attack vectors for bounded-entanglement adversaries needs to explicitly rule out joint strategies where the prover prepares a single entangled state across all qubits to correlate commitment successes. The current bound on adversarial acceptance probability decaying as exp(-c k) relies on this lift; if parallel correlations allow a higher acceptance rate, the exponential decay and 3.7% noise robustness would not hold at the claimed rate. Please provide the explicit calculation or lemma showing that the parallel attack probability is bounded by the sequential one under the no-signalling assumption.
minor comments (2)
  1. [Abstract] Abstract: The claim of 'first fully loss-tolerant single-shot QPV' should briefly reference the precise prior works it improves upon to avoid any ambiguity in the novelty statement.
  2. [Abstract] The noise robustness figure of 3.7% is stated without an accompanying equation or table reference in the abstract; adding a pointer to the relevant derivation in the main text would improve clarity.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for their constructive feedback. We are grateful for the positive assessment of the significance of our results. We address the major comment below.

read point-by-point responses

  1. Referee: [Section 3] Section 3 (No-Signalling Lift to Parallel Regime): The argument that no-signalling correlations suffice to extend the commitment security from sequential to parallel execution without introducing new attack vectors for bounded-entanglement adversaries needs to explicitly rule out joint strategies where the prover prepares a single entangled state across all qubits to correlate commitment successes. The current bound on adversarial acceptance probability decaying as exp(-c k) relies on this lift; if parallel correlations allow a higher acceptance rate, the exponential decay and 3.7% noise robustness would not hold at the claimed rate. Please provide the explicit calculation or lemma showing that the parallel attack probability is bounded by the sequential one under the no-signalling assumption.

    Authors: We agree with the referee that an explicit demonstration is necessary to fully substantiate the lift. In the revised manuscript, we will insert a dedicated lemma in Section 3 that proves, under the no-signalling assumption, that the acceptance probability for any parallel strategy is at most that of the corresponding sequential strategy for bounded-entanglement adversaries. The lemma rules out beneficial joint entanglement strategies by showing that no-signalling implies the marginals on individual commitments are independent of the others in a way that prevents correlation-based boosting of the threshold-k success rate. This preserves the exponential decay exp(-c k) and the 3.7% noise tolerance. We believe this addition will address the concern directly. revision: yes

Circularity Check

0 steps flagged

Minor self-citation to sequential protocol; parallel lift uses independent no-signalling argument without reduction to inputs

full rationale

The paper cites Phys. Rev. Lett. 135, 260801 for the sequential commitment modification and applies standard no-signalling correlations to extend it to parallel execution while preserving BB84 QPV security against bounded-entanglement adversaries. The exponential decay claim for threshold k follows from this lift. No self-definitional equations, fitted parameters renamed as predictions, or load-bearing self-citation chains appear; the central derivation relies on external no-signalling principles and prior security results that are not shown to reduce to the present paper's own fitted values or definitions. This is a normal minor self-citation case with independent content remaining.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the standard no-signalling principle of quantum mechanics to extend commitments to parallel executions and on the pre-existing security of the BB84-based QPV protocol against bounded-entanglement adversaries. No free parameters or new entities are introduced.

axioms (1)
  • standard math Quantum mechanics obeys the no-signalling principle
    Invoked to lift the commitment modification to the parallel regime while preserving security.

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discussion (0)

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