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arxiv: 2606.13667 · v1 · pith:FPQTZB5Jnew · submitted 2026-06-11 · 🪐 quant-ph

Semi-Device-Independent Certification for Nonlocality without Entanglement

Hanwool Lee , Joonwoo Bae This is my paper

Pith reviewed 2026-06-27 06:14 UTC · model grok-4.3

classification 🪐 quant-ph
keywords nonlocality without entanglementmaximum-confidence discriminationsemi-device-independent certificationseparable statesglobal measurementsquantum state discriminationquantum nonlocality
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The pith

Global measurements outperform separable ones in maximum-confidence discrimination of separable states, certifying nonlocality without entanglement semi-device-independently.

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

The paper studies how to tell apart collections of separable quantum states by guessing which state was prepared after a measurement. It finds that measurements acting jointly on all parts of the system reach a higher probability of guessing correctly given the outcome than measurements that act separately on each part. This performance gap shows nonlocality without entanglement expressed through detection . Because the gap appears only in the recorded outcomes, it can be used to certify that global operations occurred without needing full knowledge of the devices. The same approach works even when detectors miss some events, opening the way to tests with ordinary laboratory equipment.

Core claim

For ensembles composed of separable states, global measurements achieve strictly higher maximum confidence than any separable measurements, where maximum confidence is the highest probability of a correct state identification conditional on a given detection outcome. This gap certifies the presence of global operations and thereby establishes nonlocality without entanglement in a semi-device-independent manner. The certification relies solely on the statistics of detected events and therefore remains valid under non-unit detection efficiency.

What carries the argument

Maximum-confidence discrimination, the strategy that maximizes the conditional probability of a correct state guess given a measurement outcome, applied to ensembles of separable states to expose an advantage of global over separable operations.

If this is right

  • Verifying the higher confidence value certifies that global measurements were used, without assuming anything further about the devices.
  • Nonlocality without entanglement can be demonstrated in the laboratory with current detectors even when some events go undetected.
  • The same framework covers both minimum-error and unambiguous discrimination as special cases of maximum-confidence discrimination.
  • The certification procedure depends only on the recorded outcomes, so it applies directly to imperfect but standard quantum optics setups.

Where Pith is reading between the lines

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

  • The same confidence-gap test might be adapted to certify other device-independent features in quantum communication protocols that use only separable resources.
  • One could ask whether the advantage persists when the ensemble states are allowed to have small amounts of entanglement, providing a quantitative bridge between separable and entangled regimes.
  • Practical implementations could combine this certification with existing quantum key distribution hardware to add a nonlocality-without-entanglement layer at low additional cost.

Load-bearing premise

The states in the ensemble are all separable and any advantage in conditional correctness probability arises only from the global character of the measurement and is visible in the detected outcomes alone.

What would settle it

An experiment on an ensemble of separable states in which the highest conditional correctness probability obtained with global measurements equals the highest value obtained with separable measurements would falsify the central claim.

Figures

Figures reproduced from arXiv: 2606.13667 by Hanwool Lee, Joonwoo Bae.

Figure 1
Figure 1. Figure 1: The scenario of comparing the capabilities of [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Given an outcome rate ηx, the certifiable MC for antiparallel states in Eq. (3) is shown. In a noiseless state preparation, the certifiable MC with SEP is 3/4. For an outcome rate ηx < 1/3, NLWE can be certified if Cˆx > 3/4 (region I and II). For an outcome rate ηx ≤ 1/5, the gap ∆x is maximal (region I). When outcomes are so frequent ηx ≥ 1/3, NLWE cannot be certified (region III). where λ and N are dual… view at source ↗
Figure 3
Figure 3. Figure 3: The rate of inconclusive outcomes η (G) 0 for a noisy POVM in Eq. (22) (solid) is strictly lower than the rate by SEP (dotted) whenever p > 0. Note that when θ = π/12, at which p ≈ 0.58, POVM elements {Mf(G) x } 4 x=1 form a complete measurement, i.e., η (G) 0 = 0. The inconclusive rate by excluding all outcomes from the POVM elements {Mf(G) x } is given by η (G) 0 = 1 − a(1 + 4γ + p 2 3 (1 − 2 sin 2θ)). (… view at source ↗
read the original abstract

In this work, we investigate maximum-confidence discrimination, which encompasses minimum-error and unambiguous discrimination, for ensembles of separable states by considering global and separable measurements. We demonstrate that global measurements outperform separable ones, thereby establishing nonlocality without entanglement (NLWE) in terms of confidence in a detection event, a fine-grained state-identification strategy that maximizes the probability of a correct guess given a measurement outcome. Conversely, verifying achievable confidence in measurement outcomes can certify global measurements, namely, semi-device-independent certification of NLWE. Our results make it feasible to experimentally demonstrate NLWE using present-day quantum measurement devices, even with non-unit detection efficiencies, since maximum-confidence measurements rely only on detected measurement outcomes.

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

0 major / 3 minor

Summary. The paper investigates maximum-confidence discrimination of ensembles of separable states, showing that global measurements can strictly outperform separable measurements in the achievable confidence for correctly guessing the state given a detection outcome. This establishes nonlocality without entanglement (NLWE) in a fine-grained, confidence-based sense. The work further develops a semi-device-independent certification protocol in which an observed confidence exceeding the separable bound certifies the use of global measurements, with the protocol conditioned only on detected events to remain valid under non-unit detection efficiency.

Significance. If the explicit ensemble constructions and derived bounds hold, the result supplies a concrete, experimentally realizable route to demonstrating and certifying NLWE that does not require entangled states or full device characterization. The approach is compatible with current quantum optics hardware and avoids post-selection bias by conditioning exclusively on registered clicks. These features address a practical barrier in the NLWE literature and provide falsifiable, quantitative predictions for the confidence gap.

minor comments (3)
  1. Abstract: the claim of a performance gap is stated without any numerical values, explicit ensemble, or quantitative comparison; adding one concrete example (e.g., the achieved confidences for a two-qubit ensemble) would make the central result immediately verifiable from the abstract.
  2. The notation for the maximum-confidence functional and the separable bound should be cross-referenced to the general definitions introduced in the opening sections to avoid ambiguity when the protocol is applied to new ensembles.
  3. Figure captions and axis labels would benefit from explicit mention of the conditioning on detected events, reinforcing that the plotted quantities are free of post-selection assumptions.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive assessment of our work on maximum-confidence discrimination of separable states and the semi-device-independent certification of nonlocality without entanglement. The recommendation for minor revision is noted. No major comments were provided in the report, so we have no specific points requiring response or revision.

Circularity Check

0 steps flagged

No significant circularity

full rationale

The derivation constructs explicit ensembles of separable states, computes the maximum-confidence values achievable by global versus separable measurements directly from the state definitions and measurement operators, and obtains the certification bound by comparing the observed conditional probability against that separable upper bound. No step defines a quantity in terms of the target result, renames a fitted parameter as a prediction, or relies on a self-citation chain for a uniqueness theorem or ansatz. The protocol conditions only on detected events and remains independent of the final certification claim.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The claim rests on the standard distinction between global and separable measurements in quantum theory and on the definition of maximum-confidence discrimination; no free parameters or new entities are introduced in the abstract.

axioms (1)
  • standard math Quantum states and measurements obey the standard postulates of quantum mechanics, including the distinction between global and separable operations.
    Invoked when comparing global versus separable measurements on separable states.

pith-pipeline@v0.9.1-grok · 5637 in / 1164 out tokens · 21903 ms · 2026-06-27T06:14:27.414465+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

34 extracted references · 2 canonical work pages

  1. [1]

    It turns out thatCx,max = ∥√ρ−1qxρx √ρ−1∥∞ with an operator norm ∥ · ∥∞; hence, an MCM can be generally realized by rank-one POVM elements

    or formulated as a semidefinite program (SDP) [25]. It turns out thatCx,max = ∥√ρ−1qxρx √ρ−1∥∞ with an operator norm ∥ · ∥∞; hence, an MCM can be generally realized by rank-one POVM elements. Measurements in Eq. (1) can be constrained with GLOBAL or SEP. LetC(G) x,max denote a confidence with measurements in GLOBAL, and C(S) x,max with measure- ments in S...

    2023

  2. [2]

    Horodecki, P

    R. Horodecki, P. Horodecki, M. Horodecki, and K. Horo- decki, Rev. Mod. Phys.81, 865 (2009)

    2009

  3. [3]

    Curty, M

    M. Curty, M. Lewenstein, and N. Lütkenhaus, Phys. Rev. Lett.92, 217903 (2004)

    2004

  4. [4]

    Acín and N

    A. Acín and N. Gisin, Phys. Rev. Lett.94, 020501 (2005)

    2005

  5. [5]

    H. M. Wiseman, S. J. Jones, and A. C. Doherty, Phys. Rev. Lett.98, 140402 (2007)

    2007

  6. [6]

    Branciard, E

    C. Branciard, E. G. Cavalcanti, S. P. Walborn, V. Scarani, and H. M. Wiseman, Phys. Rev. A85, 010301(R) (2012)

    2012

  7. [7]

    Zhang, W

    T. Zhang, W. Zhang, J.-T. Qiu, L. Huang, X. Yuan, and Q.-M. Ding, Phys. Rev. Lett.136, 090201 (2026)

    2026

  8. [8]

    A. Acín, N. Brunner, N. Gisin, S. Massar, S. Pironio, and V. Scarani, Phys. Rev. Lett.98, 230501 (2007)

    2007

  9. [9]

    C. H. Bennett, D. P. DiVincenzo, C. A. Fuchs, T. Mor, E. Rains, P. W. Shor, J. A. Smolin, and W. K. Wootters, Phys. Rev. A59, 1070 (1999)

    1999

  10. [10]

    Ha and J

    D. Ha and J. S. Kim, Journal of Physics A: Mathematical and Theoretical56, 205303 (2023)

    2023

  11. [11]

    Šupić and N

    I. Šupić and N. Brunner, Phys. Rev. A107, 062220 (2023)

    2023

  12. [12]

    Peres and W

    A. Peres and W. K. Wootters, Phys. Rev. Lett.66, 1119 (1991)

    1991

  13. [13]

    Chitambar and M.-H

    E. Chitambar and M.-H. Hsieh, Phys. Rev. A88, 020302(R) (2013)

    2013

  14. [14]

    Ha and Y

    D. Ha and Y. Kwon, npj Quantum Information7, 81 (2021)

    2021

  15. [15]

    Chitambar, R

    E. Chitambar, R. Duan, and M.-H. Hsieh, IEEE Transac- tions on Information Theory60, 1549 (2014)

    2014

  16. [16]

    C. W. Helstrom, Information and Control10, 254 (1967)

    1967

  17. [17]

    Dieks, Physics Letters A126, 303 (1988)

    D. Dieks, Physics Letters A126, 303 (1988)

    1988

  18. [18]

    S. M. Barnett and S. Croke, Advances in Optics and Photonics1, 238 (2009). 7

    2009

  19. [19]

    J. A. Bergou, Journal of Modern Optics57, 160 (2010)

    2010

  20. [20]

    Bae and L.-C

    J. Bae and L.-C. Kwek, Journal of Physics A: Mathemat- ical and Theoretical48, 083001 (2015)

    2015

  21. [21]

    P. H. Eberhard, Phys. Rev. A47, R747(R) (1993)

    1993

  22. [22]

    Brunner, N

    N. Brunner, N. Gisin, V. Scarani, and C. Simon, Phys. Rev. Lett.98, 220403 (2007)

    2007

  23. [23]

    Croke, E

    S. Croke, E. Andersson, S. M. Barnett, C. R. Gilson, and J. Jeffers, Phys. Rev. Lett.96, 070401 (2006)

    2006

  24. [24]

    S. M. Barnett, J. Jeffers, D. Pegg, O. Jedrkiewicz, and R. Loudon, in2000 International Quantum Electronics Conference(Optica Publishing Group, 2000) p. QWC1

    2000

  25. [25]

    S. M. Barnett, J. Jeffers, and D. T. Pegg, Symmetry13, 10.3390/sym13040586 (2021)

    work page doi:10.3390/sym13040586 2021

  26. [26]

    H. Lee, K. Flatt, C. Roch i Carceller, J. B. Brask, and J. Bae, Phys. Rev. A106, 032422 (2022)

    2022

  27. [27]

    Chitambar, D

    E. Chitambar, D. Leung, L. Mančinska, M. Ozols, and A. Winter, Communications in Mathematical Physics328, 303 (2014)

    2014

  28. [28]

    Flatt, H

    K. Flatt, H. Lee, C. R. I. Carceller, J. B. Brask, and J. Bae, PRX Quantum3, 030337 (2022)

    2022

  29. [29]

    Gisin and S

    N. Gisin and S. Popescu, Phys. Rev. Lett.83, 432 (1999)

    1999

  30. [30]

    I. D. Ivanovic, Physics Letters A123, 257 (1987)

    1987

  31. [31]

    Peres, Physics Letters A128, 19 (1988)

    A. Peres, Physics Letters A128, 19 (1988)

    1988

  32. [32]

    J.Pauwels, A.Pozas-Kerstjens, F.DelSanto,andN.Gisin, Phys. Rev. X15, 021013 (2025)

    2025

  33. [33]

    Gisin, Entropy21, 10.3390/e21030325 (2019)

    N. Gisin, Entropy21, 10.3390/e21030325 (2019). APPENDIX Appendix A: Structure of maximum-confidence measurements In this Appendix, we briefly review the structure of maximum-confidence measurements (MCMs). For an ensemble of states{qx, ρx}n x=1, where qx denotesa priori probability, an MCM is obtained from the optimization problem, Cx,max = max Mx≥0 qxtr[...

    work page doi:10.3390/e21030325 2019

  34. [34]

    We have solved the certifiable maximum confidence for the low outcome rate region, ˆC(G) x,max = 1,forη x ∈(0,1/5] Case 2:0< λ <4 Let us consider the second case,0< λ < 4

    In this region, the certifiable maximum confidence by GLOBAL measurement is1. We have solved the certifiable maximum confidence for the low outcome rate region, ˆC(G) x,max = 1,forη x ∈(0,1/5] Case 2:0< λ <4 Let us consider the second case,0< λ < 4. Note that the eigenvalues νi(λ)are monotonically increasing in λ for all i. We find that, when0 < λ < 4, ν1...