REVIEW 2 major objections 5 minor 65 references
Coherent control of a channel's own dilations revives temporal Bell nonclassicality deeper into noise than control of independent environments.
Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →
T0 review · grok-4.5
2026-07-11 04:26 UTC pith:U5T33ALG
load-bearing objection Clean analytic comparison: dilation-level coherent control of the ADC revives temporal CHSH up to γ≃0.83, beating independent-environment control at ≃0.65, and the math checks out. the 2 major comments →
Coherent Control of Channel Dilations Activate Temporal Bell Nonclassicality
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Coherent control of two unitarily equivalent Stinespring dilations of the amplitude-damping channel revives temporal CHSH violation from the deterministic threshold γ = 0.5 all the way to γ ≃ 0.83, strictly beyond the γ ≃ 0.65 reachable by coherent control of independent-environment realizations of the same channel, even though both constructions produce identical reduced dynamics when used without control.
What carries the argument
Coherent control of unitarily equivalent Stinespring dilations: a control qubit places the system–environment unitaries U_SE(θ) and U_SE(−θ) in superposition; post-selection on the control then yields conditional maps that cleanly separate the Kraus operators and generate stronger interference than independent-environment superpositions.
Load-bearing premise
The concrete pair of dilations—one unitary and its inverse—must be experimentally realizable with post-selection whose success probability stays independent of the first measurement setting; if that engineering fails, the extended activation range disappears.
What would settle it
Implement both the independent-environment and the equivalent-dilation coherent-control protocols for amplitude damping on a controllable qubit platform and measure the temporal CHSH value versus damping strength; the dilation protocol must continue to violate past γ ≈ 0.65 and up to ≈ 0.83 while the independent-environment protocol does not.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper shows that coherent control of noisy evolutions can revive temporal CHSH violations suppressed by amplitude damping. It compares two constructions that realize the same reduced ADC deterministically: (i) coherent control of independent system–environment interactions and (ii) coherent control of two unitarily equivalent Stinespring dilations (U_SE( heta) and U_SE(- heta)). Post-selection on the control yields distinct conditional maps; analytic expressions for the temporal CHSH parameter (Eqs. 53–54) and the associated Choi operators (Appendix A) show that dilation-level control extends violation from the deterministic threshold γ_c=0.5 up to γ≃ 0.83, strictly beyond the γ≃ 0.65 reachable with independent environments. Under setting-independent post-selection (X–Y measurements), the same activation certifies that the ADC is not strongly CHSH nonlocality-breaking in that range. The work therefore identifies the choice of Stinespring dilation as an operationally relevant resource for temporal nonclassicality tests.
Significance. If correct, the result supplies a concrete, analytically controlled mechanism by which implementation-level distinctions among Stinespring dilations become operationally visible under coherent control, even though they are invisible for deterministic channel use. The explicit comparison of activation thresholds (0.5 vs ≃0.65 vs ≃0.83), the matching with the optimal filtering threshold of Ref. [42] via an entirely different physical route, and the clean link to strong nonlocality-breaking via setting-independent post-selection are all valuable. The derivations are fully explicit (conditional channels, success probabilities, Choi matrices and correlation tensors), which makes the central claim falsifiable and reproducible. The paper therefore advances both the theory of temporal Bell inequalities under noise and the broader program of coherent control of quantum processes.
major comments (2)
- Sec. III B and Eqs. (32)–(33): the dilation-level construction is specialized to the single pair U_SE( heta) and U_SE(- heta) (i.e., one particular environment unitary V_E). While this choice is natural (reverse Hamiltonian, Kraus separation K0 vs K1) and already demonstrates a clear advantage over independent-environment control, the broader claim that “the choice of Stinespring dilation is an operationally relevant resource” would be stronger if the manuscript either (a) optimized over a one-parameter family of V_E or (b) briefly argued why other unitarily equivalent dilations cannot improve (or can only degrade) the activation range. A short remark or numerical scan would close this gap without changing the central result.
- Sec. IV and Appendix A: the main-text expression S^D_T = 4√(2-2γ)/(2-γ) (Eq. 54) and the quoted threshold γ_c≃0.83 are obtained with the fixed equatorial measurement set of Eq. (6). The conditional Choi operator (A13) itself admits a larger CHSH value (violation for all γ<1) when measurements are allowed in the X–Z plane, but those measurements make the post-selection probability setting-dependent. This distinction is explained only at the end of the Appendix; it should be stated explicitly in Sec. IV so that readers do not misinterpret Eq. (54) as the absolute maximum of the conditional Choi state, which would affect the nonlocality-breaking certification claim.
minor comments (5)
- Section headings contain spurious spaces (“IMPLEMENTA TIONS”, “ACTIV A TION THRESHOLDS”); these should be corrected.
- Fig. 1 caption and labels refer to environments E1 and E2 while the text (Eqs. 14–15) uses E0 and E1; unify the notation.
- Fig. 1 and Fig. 3: the phrases “which path qubit” and “Coherent recombiner” would read more cleanly as “which-path qubit” and “coherent recombiner”.
- A one-sentence experimental outlook (possible platforms for controlled U and U†, sensitivity to control decoherence) would help readers assess the practical reach of the dilation-level advantage; this can remain brief.
- In Appendix A the formatting of the closed-form S expressions (e.g., “8√2-2γ/4-γ”) is occasionally ambiguous in plain text; ensure the published version uses unambiguous LaTeX fractions.
Circularity Check
No significant circularity: activation thresholds are derived from explicit post-selected Choi operators and Kraus structure, not presupposed or fitted.
full rationale
The paper's central claims (activation of temporal CHSH violation to γ_c ≃ 0.65 under independent-environment coherent control and to γ_c ≃ 0.83 under coherent control of unitarily equivalent Stinespring dilations of the ADC) follow by direct calculation from the definitions of the controlled unitaries W_ind and W_D, the resulting unnormalized conditional maps eE_ind_± and eE_D_± (Eqs. 23, 27, 43, 47), and the associated normalized Choi operators (Appendix A, Eqs. A9 and A13). The S_T expressions (Eqs. 53–54) are obtained from the two largest eigenvalues of the correlation matrices T_ind and T_D without any free parameters fitted to data or to the target thresholds. The coincidence with the optimal filtering threshold of Ref. [42] is reported a posteriori and is not used as an input. Self-citations (e.g., [54]) supply related context on coherent control of unitaries for LGI but are not load-bearing for the temporal-CHSH derivations, which remain self-contained against the standard Stinespring dilation of the ADC and the temporal CHSH definition. No step reduces by construction to its own inputs.
Axiom & Free-Parameter Ledger
axioms (4)
- standard math Every CPTP map admits a Stinespring dilation by a unitary interaction with an environment initialized in a pure state.
- domain assumption The temporal CHSH parameter S_T ≤ 2 under the assumptions of macrorealism and non-invasive measurability.
- domain assumption The amplitude-damping channel is realized by the two Kraus operators K_0, K_1 given in Eqs. 7–8, equivalently by the unitary U_SE(θ) of Eq. 12.
- domain assumption Post-selection on a control qubit measured in the Hadamard basis is an allowed operation that yields a (generally non-trace-preserving) conditional map on the system.
read the original abstract
The temporal Clauser-Horne-Shimony-Holt (CHSH) inequality witnesses the nonclassicality of temporal correlations, but its violation is generally degraded by environmental noise. Here, we show that violation of the temporal CHSH inequality can be revived through coherent control of noisy quantum evolutions. We compare two physically distinct implementations: coherent control of noisy evolutions induced by interaction of the system with independent environments, and coherent control of two physically distinct, unitarily equivalent Stinespring dilations of the same noisy channel. Although these constructions generate identical deterministic system dynamics, they induce distinctly different post-selected evolutions. With a focus on the amplitude damping channel (ADC), we show that coherent control of equivalent dilations extend the range of temporal CHSH inequality violation well beyond both the incoherently controlled, or deterministic, scenario and what is achievable with independent environments. Under setting-independent post-selection of the coherent control implementation, the resulting violation further certifies that the channel is not strongly CHSH nonlocality-breaking. Our results identify the choice of Stinespring dilation as an operationally relevant resource in coherently controlled tests of temporal quantum correlations.
Figures
Reference graph
Works this paper leans on
-
[1]
Prepare the control in a maximally incoherent state, i.e., ρC(0) = (|0⟩⟨0|C +|1⟩⟨1|C ) 2 . In this case, the joint state of the control- system after the controlled evolution is given as |0⟩⟨0|C +|1⟩⟨1| C 2 ⊗ E θ(Ma|Ai ρ0M † a|Ai )where the two distinct branches implement the same ADC. Now, pro- jecting the control in the Hadamard basis{|±⟩}, with project...
-
[2]
6 The post-measurement stateM a|Ai ρ0M † a|Ai and the control state are evolved jointly, after which the control state is pro- jected onto,Π ± =|±⟩ ⟨±|C, and traced out
Prepare the control in the coherent state ρC(0) =|+⟩ ⟨+| C. 6 The post-measurement stateM a|Ai ρ0M † a|Ai and the control state are evolved jointly, after which the control state is pro- jected onto,Π ± =|±⟩ ⟨±|C, and traced out. Forρ 0 = I 2, the corresponding (unnormalized) two-time probability becomes, eP±(a, b|Ai, Bj) = 1 2Tr h Mb|Bj eE ind ± (Ma|Ai) ...
-
[3]
The corre- sponding unnormalizedconditionalchannel can then be writ- ten as, eE D ± (ρS) = TrE h AD ± (ρS ⊗ |0⟩⟨0|E)A D† ± i .(42) Expanding Eq
After applyingW D and tracing outE, the joint state becomes ρD CS =1 2 |0⟩ ⟨0|C ⊗ E00(ρS) +|1⟩ ⟨1|C ⊗ E11(ρS) ± 1 2 |0⟩ ⟨1|C ⊗Γ 01(ρS) +|1⟩ ⟨0|C ⊗Γ 10(ρS) , (40) Equivalently, analogous to the independent environment case, we can define theeffectivesystem–environment oper- ators associated with the two control outcomes±as, AD ± = 1 2 (U0 ±U 1).(41) Notice...
-
[4]
Prepare the control in a maximally incoherent mixed state, i.e.,ρ C(0) = (|0⟩⟨0|C +|1⟩⟨1|C ) 2 . Analogous to the corresponding scenario in the case of co- herent control of superposition arising due to independent en- vironments, here too the control only implements a classical random selection between the two unitarily equivalent Stine- spring dilations...
-
[5]
Prepare the control in the|+⟩ C state: Here too, after jointly evolving the system and the control, post-selecting the control before tracing it out, the two-time (unnormalized) probabilities can be calculated using the ex- pression, eP(a, b|A i, Bj) = 1 2Tr h Mb|Bj eE D ±(Ma|Ai) i .(52) The success probability of the post-selected control mea- surement i...
2023
-
[6]
J. S. Bell,Speakable and Unspeakable in Quantum Mechanics, 2nd ed. (Cambridge University Press, 2004)
2004
-
[7]
C. Brukner, S. Taylor, S. Cheung, and V . Vedral (2004), arXiv.quant-ph/0402127
work page internal anchor Pith review Pith/arXiv arXiv 2004
-
[8]
Fritz, New Journal of Physics12, 083055 (2010)
T. Fritz, New Journal of Physics12, 083055 (2010)
2010
-
[9]
J. F. Clauser, M. A. Horne, A. Shimony, and R. A. Holt, Phys. Rev. Lett.23, 880 (1969)
1969
-
[10]
A. J. Leggett and A. Garg, Phys. Rev. Lett.54, 857 (1985)
1985
-
[11]
Emary, N
C. Emary, N. Lambert, and F. Nori, Rep. Prog. Phys.77, 016001 (2014)
2014
-
[12]
J. J. Halliwell, Physical Review A93, 022123 (2016)
2016
-
[13]
J. J. Halliwell, Physical Review A96, 012121 (2017)
2017
-
[14]
Zhang, X
Y . Zhang, X. Tan, and T. Qiu, Quantum Information Processing 22, 354 (2023)
2023
-
[15]
Kofler and C
J. Kofler and C. Brukner, Phys. Rev. A87, 052115 (2013)
2013
-
[16]
Palacios-Laloy, F
A. Palacios-Laloy, F. Mallet, F. Nguyen, P. Bertet, D. Vion, D. Esteve, and A. N. Korotkov, Nature Physics6, 442 (2010)
2010
-
[17]
Athalye, S
V . Athalye, S. S. Roy, and T. S. Mahesh, Phys. Rev. Lett.107, 130402 (2011)
2011
-
[18]
Katiyar, A
H. Katiyar, A. Shukla, K. R. K. Rao, and T. S. Mahesh, Phys. Rev. A87, 052102 (2013)
2013
-
[19]
Waldherr, P
G. Waldherr, P. Neumann, S. F. Huelga, F. Jelezko, and J. Wrachtrup, Phys. Rev. Lett.107, 090401 (2011)
2011
-
[20]
Dressel, C
J. Dressel, C. J. Broadbent, J. C. Howell, and A. N. Jordan, Phys. Rev. Lett.106, 040402 (2011)
2011
-
[21]
Z.-Q. Zhou, S. F. Huelga, C.-F. Li, and G.-C. Guo, Phys. Rev. Lett.115, 113002 (2015)
2015
-
[22]
T. Zhan, C. Wu, M. Zhang, Q. Qin, X. Yang, H. Hu, W. Su, J. Zhang, T. Chen, Y . Xie, W. Wu, and P. Chen, Phys. Rev. A 107, 012424 (2023)
2023
-
[23]
Tusun, W
M. Tusun, W. Cheng, Z. Chai, Y . Wu, Y . Wang, X. Rong, and J. Du, Phys. Rev. A105, 042613 (2022)
2022
-
[24]
Fedrizzi, M
A. Fedrizzi, M. P. Almeida, M. A. Broome, A. G. White, and M. Barbieri, Physical Review Letters106, 200402 (2011)
2011
-
[25]
Waldherr, P
G. Waldherr, P. Neumann, S. F. Huelga, F. Jelezko, and J. Wrachtrup, Physical Review Letters107, 090401 (2011)
2011
-
[26]
C. Spee, H. Siebeneich, T. F. Gloger, P. Kaufmann, M. Johan- ning, M. Kleinmann, C. Wunderlich, and O. Gühne, New Jour- nal of Physics22, 023028 (2020)
2020
-
[27]
Rosset, F
D. Rosset, F. Buscemi, and Y .-C. Liang, Physical Review X8, 021033 (2018)
2018
-
[28]
Budroni, G
C. Budroni, G. Vitagliano, and M. P. Woods, Physical Review Research3, 033051 (2021)
2021
-
[29]
K.-D. Wu, Z. Hou, G.-Y . Xiang, C.-F. Li, G.-C. Guo, D. Dong, and F. Nori, npj Quantum Information6, 55 (2020)
2020
-
[30]
G. D. Berk, A. J. P. Garner, B. Yadin, K. Modi, and F. A. Pol- lock, Quantum5, 435 (2021)
2021
-
[31]
Zukowski, Frontiers of Physics9, 629 (2014)
M. .Zukowski, Frontiers of Physics9, 629 (2014)
2014
-
[32]
A. G. Maity, S. Mal, C. Jebarathinam, and A. S. Majumdar, Physical Review A103, 062604 (2021)
2021
-
[33]
M. F. Pusey, Journal of the Optical Society of America B32, A56 (2015)
2015
-
[34]
G. C. Knee, K. Kakuyanagi, M.-C. Yeh, Y . Matsuzaki, H. Toida, H. Yamaguchi, S. Saito, A. J. Leggett, and W. J. Munro, Nature Communications7, 13253 (2016)
2016
-
[35]
Huffman and A
E. Huffman and A. Mizel, Physical Review A95, 032131 (2017)
2017
-
[36]
M. B. Ruskai, Reviews in Mathematical Physics15, 643 (2003)
2003
-
[37]
Horodecki, P
M. Horodecki, P. W. Shor, and M. B. Ruskai, Reviews in Math- ematical Physics15, 629 (2003)
2003
-
[38]
R. Uola, A. C. S. Costa, H. C. Nguyen, and O. Gühne, Rev. Mod. Phys.92, 015001 (2020)
2020
-
[39]
Du, H.-W
M.-M. Du, H.-W. Li, S.-T. Shen, X.-J. Yan, X.-Y . Li, L. Zhou, W. Zhong, and Y .-B. Sheng, Quantum Information Processing 24, 395 (2025)
2025
-
[40]
Srivastav, N
V . Srivastav, N. H. Valencia, W. McCutcheon, S. Leedumrong- watthanakun, S. Designolle, R. Uola, N. Brunner, and M. Ma- lik, Physical Review X12, 041023 (2022)
2022
-
[41]
Brunner, D
N. Brunner, D. Cavalcanti, S. Pironio, V . Scarani, and S. Wehner, Rev. Mod. Phys.86, 419 (2014)
2014
-
[42]
Pal and S
R. Pal and S. Ghosh, Journal of Physics A: Mathematical and Theoretical48, 155302 (2015)
2015
-
[43]
Kim, J.-C
Y .-S. Kim, J.-C. Lee, O. Kwon, and Y .-H. Kim, Nature Physics 8, 117 (2012)
2012
-
[44]
Hirsch, M
F. Hirsch, M. T. Quintino, J. Bowles, and N. Brunner, Phys. Rev. Lett.111, 160402 (2013)
2013
-
[45]
Pramanik, Y .-W
T. Pramanik, Y .-W. Cho, S.-W. Han, S.-Y . Lee, Y .-S. Kim, and S. Moon, Phys. Rev. A99, 030101(R) (2019)
2019
-
[46]
Z.-Y . Hao, Y . Wang, J.-K. Li, Y . Xiang, Q.-Y . He, Z.-H. Liu, M. Yang, K. Sun, J.-S. Xu, C.-F. Li, and G.-C. Guo, Phys. Rev. A109, 022411 (2024)
2024
-
[47]
Ku, H.-C
H.-Y . Ku, H.-C. Weng, Y .-A. Shih, P.-C. Kuo, N. Lambert, F. Nori, C.-S. Chuu, and Y .-N. Chen, Phys. Rev. Research3, 11 043083 (2021)
2021
-
[48]
H. S. Karthik, S. Gómez, F. M. Quinteros, Akshata Shenoy H., M. Pawłowski, S. P. Walborn, G. Lima, and E. S. Gómez, Phys. Rev. A111, 032613 (2025)
2025
-
[49]
D. K. L. Oi, Phys. Rev. Lett.91, 067902 (2003)
2003
-
[50]
Gui-Lu, Communications in Theoretical Physics45, 825 (2006)
L. Gui-Lu, Communications in Theoretical Physics45, 825 (2006)
2006
-
[51]
Chiribella and H
G. Chiribella and H. Kristjánsson, Proceedings of the Royal So- ciety A475, 20180903 (2019)
2019
-
[52]
A. A. Abbott, J. Wechs, D. Horsman, M. Mhalla, and C. Bran- ciard, Quantum4, 333 (2020)
2020
-
[53]
A. O. Pang, N. Lupu-Gladstein, H. Ferretti, Y . B. Yilmaz, A. Brodutch, and A. M. Steinberg, Quantum7, 1125 (2023)
2023
-
[54]
García-Díaz, K
M. García-Díaz, K. Fang, X. Wang, M. Rosati, M. Skotiniotis, J. Calsamiglia, and A. Winter, Quantum2, 100 (2018)
2018
-
[55]
Rubino, L
G. Rubino, L. A. Rozema, D. Ebler, H. Kristjánsson, S. Salek, P. A. Guérin, A. A. Abbott, C. Branciard, ˇC. Brukner, G. Chiri- bella,et al., Physical Review Research3, 013093 (2021)
2021
-
[56]
Gui-Lu and L
L. Gui-Lu and L. Yang, Communications in Theoretical Physics 50, 1303 (2008)
2008
-
[57]
Lee, J.-D
K.-Y . Lee, J.-D. Lin, A. Miranowicz, F. Nori, H.-Y . Ku, and Y .-N. Chen, Phys. Rev. Res.5, 013103 (2023)
2023
-
[58]
X. Yuan, Y . Liu, Q. Zhao, B. Regula, J. Thompson, and M. Gu, npj Quantum Information7, 108 (2021)
2021
-
[59]
Chatterjee, H
A. Chatterjee, H. S. Karthik, T. S. Mahesh, and A. R. Usha Devi, Phys. Rev. Lett.135, 220202 (2025)
2025
-
[60]
M. A. Nielsen and I. L. Chuang,Quantum Computation and Quantum Information(Cambridge University Press, 2010)
2010
-
[61]
Jamiołkowski, Reports on Mathematical Physics3, 275 (1972)
A. Jamiołkowski, Reports on Mathematical Physics3, 275 (1972)
1972
-
[62]
Choi, Linear Algebra and its Applications10, 285 (1975)
M.-D. Choi, Linear Algebra and its Applications10, 285 (1975)
1975
-
[63]
H.-Y . Ku, J. Kadlec, A. ˇCernoch, M. T. Quintino, W. Zhou, K. Lemr, N. Lambert, A. Miranowicz, S.-L. Chen, F. Nori, and Y .-N. Chen, PRX Quantum3, 020338 (2022)
2022
-
[64]
Horodecki, P
R. Horodecki, P. Horodecki, and M. Horodecki, Physics Letters A200, 340 (1995)
1995
-
[65]
Verstraete and M
F. Verstraete and M. M. Wolf, Phys. Rev. Lett.89, 170401 (2002). Appendix A: Choi Matrix and Non-locality breaking channels To understand the connection between temporal CHSH violations and nonlocality-breaking property of the quan- tum channels, we consider it useful to employ the Choi– Jamiołkowski representation of quantum channels [55–57]. For a qubit...
2002
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.