Loss-Tolerant Quantum Communication via Bosonic-GKP-Parity-Encoding
Pith reviewed 2026-05-10 17:46 UTC · model grok-4.3
The pith
GKP-based repeaters enable loss-tolerant quantum communication comparable to photonic systems but with far fewer qubits.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The paper shows that GKP-based repeaters, through a teleamplifier protocol and a CBSM scheme with modified parity encoding, continuous-variable measurements, and clipping, can correct transmission loss without logical errors. This enables medium-distance quantum communication and produces secure key rates comparable to photonic approaches but requiring orders of magnitude fewer qubits.
What carries the argument
The concatenated Bell state measurement scheme with GKP parity encoding and clipping method, supported by the teleamplifier protocol for loss correction.
If this is right
- Transmission loss is suppressed across three protocols, with the teleamplifier being optimal for medium distances.
- The CBSM scheme corrects loss without logical errors and extends transmission distance significantly.
- Secure key rates are computed using analog syndrome information from the GKP code.
- GKP repeaters achieve performance comparable to photonic qubit methods with orders of magnitude fewer qubits.
Where Pith is reading between the lines
- Such encoding could lower the barrier to implementing quantum networks by reducing the number of physical qubits needed.
- Similar techniques might be adapted for other lossy channels in quantum sensing or distributed computing.
- Hybrid systems combining GKP with other codes could push communication distances further.
Load-bearing premise
The teleamplifier protocol and the CBSM scheme with clipping can correct transmission loss without introducing logical errors or needing higher-level encoding.
What would settle it
An experiment that implements the proposed CBSM with clipping on GKP states and measures either the presence of logical errors or key rates below the predicted values in a lossy medium would falsify the claims.
Figures
read the original abstract
Quantum repeaters constitute a promising platform for enabling long distance quantum communication and may ultimately serve as the backbone of a secure quantum internet, a scalable quantum network, or a distributed quantum computer. An efficient approach to encoding qubits within an error-correcting code is provided by bosonic codes, in which even a single oscillator mode can function as a sufficiently large physical system. In this work, initially we focus on the bosonic Gottesman Kitaev Preskill (GKP) code as a natural candidate for loss correction based quantum repeaters, which can be implemented at room temperature. We demonstrate that transmission loss can be suppressed across three related protocols at the expense of the introduction of logical errors. The third protocol, where a relay-like teleamplifier is applied is optimal. This approach enables medium-distance quantum communication without requiring higher level encoding. We compute the resulting secure key rates while leveraging analog syndrome information. Furthermore, we propose a concatenated Bell state measurement (CBSM) scheme with a modified parity encoding based on GKP qubits, CV measurement and a clipping method that corrects transmission loss without introducing logical errors. This significantly enhances the possible transmission distance. We find that GKP based repeaters can achieve performance comparable to approaches relying on photonic qubits, while requiring orders of magnitude fewer qubits.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper proposes three protocols for loss-tolerant quantum repeaters based on bosonic GKP codes with parity encoding. It shows that transmission loss can be suppressed (at the cost of logical errors) in the first two protocols, with the third (relay-like teleamplifier) being optimal for medium distances without higher-level encoding. It further introduces a concatenated Bell-state measurement (CBSM) scheme using modified parity encoding, CV measurements, and a clipping method that is claimed to correct loss with no logical errors. Secure key rates are computed using analog syndrome information, and the work concludes that GKP-based repeaters achieve performance comparable to photonic-qubit approaches while using orders of magnitude fewer qubits.
Significance. If the central claims on zero-logical-error loss correction via CBSM clipping and the resulting key-rate curves hold, the result would be significant: it would demonstrate a resource-efficient, room-temperature bosonic route to medium-distance quantum communication that substantially reduces the physical-qubit overhead relative to discrete-variable photonic repeaters. The use of analog syndrome information and the explicit comparison to photonic baselines would strengthen the case for bosonic codes in repeater architectures.
major comments (2)
- [CBSM scheme description] CBSM scheme description (near end of manuscript): the assertion that the clipping operation in the concatenated Bell-state measurement corrects transmission loss 'without introducing logical errors' is load-bearing for the headline qubit-count advantage and the claim of enhanced transmission distance. No explicit logical-error probability, fidelity calculation, or threshold derivation as a function of loss parameter or distance is supplied; without this, it is impossible to verify that the residual logical-error floor remains zero (or below the photonic baseline) rather than growing with distance.
- [Performance comparison section] Performance comparison section: the statement that GKP repeaters achieve 'performance comparable to approaches relying on photonic qubits' while requiring 'orders of magnitude fewer qubits' rests on the secure-key-rate curves. These curves must be shown explicitly against the relevant photonic baselines (including error budgets and finite-key effects) to substantiate the quantitative advantage; the current high-level description does not allow assessment of whether the advantage survives realistic analog-syndrome noise or finite block lengths.
minor comments (2)
- [Abstract] Abstract: the three protocols are introduced at a high level; a brief sentence clarifying the key difference between the second and third protocols (teleamplifier) would improve readability.
- [CBSM scheme description] Notation: the distinction between the 'modified parity encoding' used in CBSM and the standard GKP parity code should be defined explicitly on first use to avoid confusion with existing GKP literature.
Simulated Author's Rebuttal
We thank the referee for their careful reading of the manuscript and for the constructive comments. We address each major comment below and have revised the manuscript accordingly to strengthen the presentation of the CBSM scheme and the performance comparisons.
read point-by-point responses
-
Referee: [CBSM scheme description] CBSM scheme description (near end of manuscript): the assertion that the clipping operation in the concatenated Bell-state measurement corrects transmission loss 'without introducing logical errors' is load-bearing for the headline qubit-count advantage and the claim of enhanced transmission distance. No explicit logical-error probability, fidelity calculation, or threshold derivation as a function of loss parameter or distance is supplied; without this, it is impossible to verify that the residual logical-error floor remains zero (or below the photonic baseline) rather than growing with distance.
Authors: We agree that an explicit derivation of the logical-error probability is required to substantiate the zero-logical-error claim for the CBSM clipping operation. In the revised manuscript we add a dedicated subsection deriving the post-clipping state evolution in the GKP code space. We show analytically that, for ideal infinite-squeezing GKP states and perfect CV homodyne measurements, the clipping projects onto the logical subspace without introducing Pauli errors; the only residual logical error arises from finite squeezing, which we quantify as a function of the loss parameter and the GKP squeezing level. We also supply the corresponding fidelity and threshold curves versus distance, confirming that the logical-error floor remains below the photonic baseline for the parameter regime considered. revision: yes
-
Referee: [Performance comparison section] Performance comparison section: the statement that GKP repeaters achieve 'performance comparable to approaches relying on photonic qubits' while requiring 'orders of magnitude fewer qubits' rests on the secure-key-rate curves. These curves must be shown explicitly against the relevant photonic baselines (including error budgets and finite-key effects) to substantiate the quantitative advantage; the current high-level description does not allow assessment of whether the advantage survives realistic analog-syndrome noise or finite block lengths.
Authors: We acknowledge that the original manuscript presented only high-level comparisons. In the revision we include a new figure (and accompanying table) that plots the secure key rate versus distance for the GKP-based protocols against the relevant photonic-qubit repeater baselines from the literature. The plots incorporate realistic analog-syndrome noise, finite-key effects, and the full error budget (including GKP squeezing imperfections and measurement noise). This allows direct quantitative verification of the qubit-count advantage while remaining within the same security model. revision: yes
Circularity Check
No circularity: protocols and key-rate claims rest on explicit new constructions rather than self-definition or fitted inputs.
full rationale
The paper defines three loss-suppression protocols (including the teleamplifier and CBSM with clipping) from first principles using standard GKP code properties, then computes secure key rates from the resulting error models and analog syndrome information. No equation reduces a claimed prediction to a fitted parameter by construction, no uniqueness theorem is imported from the authors' prior work, and no ansatz is smuggled via self-citation. The central performance comparison (comparable rates with fewer qubits) follows directly from the described protocols without requiring the target result as an input.
Axiom & Free-Parameter Ledger
axioms (2)
- domain assumption Bosonic GKP code provides natural loss correction for quantum repeaters implementable at room temperature
- standard math Standard quantum optical models of transmission loss and continuous-variable measurements
Lean theorems connected to this paper
-
IndisputableMonolith/Cost/FunctionalEquationwashburn_uniqueness_aczel unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We propose a concatenated Bell-state measurement (CBSM) scheme with a modified parity encoding based on GKP qubits, CV measurement and a clipping method that corrects transmission loss without introducing logical errors.
-
IndisputableMonolith/Foundation/BranchSelectionbranch_selection unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
the clipping method... Pμup = PCClip / (PCClip + PINCClip) ... Eμup = 1 − Pμup
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
Works this paper leans on
-
[1]
Gottesman-Kitaev-Preskill qubit a. Ideal GKP qubit Let ˆq= (ˆa+ ˆa†) and ˆp=i(ˆa† −ˆa) be the position and momentum operators of a bosonic mode, where ˆaand ˆa† are annihilation and creation operators satisfying [ˆa,ˆa†] = 1. We define the GKP qubit as the two-dimensional subspace of a bosonic Hilbert space that is stabilized by the two stabilizers ˆSq =Z...
-
[2]
T eleportation-based GKP Error Correction a. Additional calculation on Teleportation-based GKP error correction using Ideal GKP states As the teleportation-based GKP error correction is based on beam-splitter interactions. Under the beamsplitter interaction ˆBk→l(π/4), position eigenstates are transformed as ˆBk→l |ˆqk =q k⟩ |ˆql =q l⟩= qk −q l√ 2 qk +q l...
-
[3]
Bell-state Measurement of GKP qubits The computational basis states of the ideal GKP qubit are given by |¯0⟩GKP ≡ X n∈Z ˆq= 2n√π (B1) |¯1⟩GKP ≡ X n∈Z ˆq= (2n+ 1)√π (B2) | ¯+⟩GKP ≡ X n∈Z ˆp= 2n√π (B3) | ¯−⟩GKP ≡ X n∈Z ˆp= (2n+ 1)√π (B4) |¯0⟩GKP ≡ X n∈Z ˆq= 2n√π (B5) ≡ X n∈Z δ(q−2n √π)|q⟩(B6) ≡ Z dp 1√ 2π X n∈Z eip2n√π |p⟩(B7) ≡ 1√ 2 X n∈Z δ(p−n √π)|p⟩(B8) ...
-
[4]
[| ¯+⟩⊗m GKP +| ¯−⟩⊗m GKP]n (B13) |1⟩L ≡[| ¯+⟩⊗m GKP − | ¯−⟩⊗m GKP]1[| ¯+⟩⊗m GKP − | ¯−⟩⊗m GKP]2
Decomposition of the Encoded Bell States In the GKP-parity-state-encoding, |0⟩L ≡[| ¯+⟩⊗m GKP +| ¯−⟩⊗m GKP]1[| ¯+⟩⊗m GKP +| ¯−⟩⊗m GKP]2 . . .[| ¯+⟩⊗m GKP +| ¯−⟩⊗m GKP]n (B13) |1⟩L ≡[| ¯+⟩⊗m GKP − | ¯−⟩⊗m GKP]1[| ¯+⟩⊗m GKP − | ¯−⟩⊗m GKP]2 . . .[| ¯+⟩⊗m GKP − | ¯−⟩⊗m GKP]n (B14) The Bell-states are written as |ϕ⟩± ≡ 1√ 2 h [| ¯+⟩⊗m GKP +| ¯−⟩⊗m GKP]1 . . .[...
-
[5]
Simulation details and discussion on logical errors of the GKP-parity-encoding Simulation details:In each block of the protocol, CBSM is performed on two GKP qubits. One of the qubits propagates between neighbouring repeater nodes over a distanceL 0, while the other remains stationary within the repeater. The success probability of this operation is denot...
-
[6]
H. J. Kimble, The quantum internet, Nature453, 1023 (2008)
work page 2008
- [7]
- [8]
-
[9]
V. Scarani, H. Bechmann-Pasquinucci, N. J. Cerf, M. Duˇ sek, N. L¨ utkenhaus, and M. Peev, The security of practical quantum key distribution, Reviews of modern physics81, 1301 (2009)
work page 2009
-
[10]
S. Pirandola, U. L. Andersen, L. Banchi, M. Berta, D. Bunandar, R. Colbeck, D. Englund, T. Gehring, C. Lupo, C. Ottaviani,et al., Advances in quantum cryp- tography, Advances in optics and photonics12, 1012 (2020)
work page 2020
-
[11]
X.-S. Ma, T. Herbst, T. Scheidl, D. Wang, S. Kropatschek, W. Naylor, B. Wittmann, A. Mech, J. Kofler, E. Anisimova,et al., Quantum teleportation over 143 kilometres using active feed-forward, Nature 489, 269 (2012)
work page 2012
-
[12]
M. K. Bhaskar, R. Riedinger, B. Machielse, D. S. Levo- nian, C. T. Nguyen, E. N. Knall, H. Park, D. Englund, M. Lonˇ car, D. D. Sukachev,et al., Experimental demon- stration of memory-enhanced quantum communication, Nature580, 60 (2020)
work page 2020
-
[13]
S. Slussarenko, M. M. Weston, L. K. Shalm, V. B. Verma, S.-W. Nam, S. Kocsis, T. C. Ralph, and G. J. Pryde, Quantum channel correction outperforming direct trans- mission, Nature Communications13, 1832 (2022)
work page 2022
-
[14]
X.-H. Zhan, Z.-Q. Zhong, J.-Y. Ma, S. Wang, Z.-Q. Yin, W. Chen, D.-Y. He, G.-C. Guo, and Z.-F. Han, Experimental demonstration of long distance quantum communication with independent heralded single photon sources, npj Quantum Information11, 73 (2025)
work page 2025
-
[15]
Yamamoto, The quantum optical repeater, Science 263, 1394 (1994)
Y. Yamamoto, The quantum optical repeater, Science 263, 1394 (1994)
work page 1994
-
[16]
H. Briegel, W. Dur, J. Cirac, and P. Zoller, Interdisci- plinary physics: Biological physics, quantum information, etc-quantum repeaters: The role of imperfect local oper- ations in quantum communication, Physical Review Let- ters81, 5932 (1998)
work page 1998
-
[17]
P. Van Loock, T. Ladd, K. Sanaka, F. Yamaguchi, K. Nemoto, W. Munro, and Y. Yamamoto, Hybrid quan- tum repeater using bright coherent light, Physical review letters96, 240501 (2006)
work page 2006
-
[18]
J. Dias and T. C. Ralph, Quantum repeaters using continuous-variable teleportation, Physical Review A95, 022312 (2017)
work page 2017
-
[19]
Z.-D. Li, R. Zhang, X.-F. Yin, L.-Z. Liu, Y. Hu, Y.-Q. Fang, Y.-Y. Fei, X. Jiang, J. Zhang, L. Li,et al., Ex- perimental quantum repeater without quantum memory, Nature photonics13, 644 (2019)
work page 2019
-
[20]
W. J. Munro, A. M. Stephens, S. J. Devitt, K. A. Harri- son, and K. Nemoto, Quantum communication without the necessity of quantum memories, Nature Photonics6, 777 (2012)
work page 2012
- [21]
-
[22]
J. Borregaard, H. Pichler, T. Schr¨ oder, M. D. Lukin, P. Lodahl, and A. S. Sørensen, One-way quantum re- peater based on near-deterministic photon-emitter inter- faces, Physical Review X10, 021071 (2020)
work page 2020
- [23]
-
[24]
P. T. Cochrane, G. J. Milburn, and W. J. Munro, Macro- scopically distinct quantum-superposition states as a bosonic code for amplitude damping, Physical Review A59, 2631 (1999)
work page 1999
-
[25]
D. Gottesman, A. Kitaev, and J. Preskill, Encoding a qubit in an oscillator, Phys. Rev. A64, 012310 (2001)
work page 2001
-
[26]
A. P. Lund, T. C. Ralph, and H. L. Haselgrove, Fault- tolerant linear optical quantum computing with small- amplitude coherent states, Physical review letters100, 030503 (2008)
work page 2008
-
[27]
N. Ofek, A. Petrenko, R. Heeres, P. Reinhold, Z. Leghtas, B. Vlastakis, Y. Liu, L. Frunzio, S. M. Girvin, L. Jiang, et al., Extending the lifetime of a quantum bit with error correction in superconducting circuits, Nature536, 441 (2016)
work page 2016
-
[28]
C. Fl¨ uhmann, T. L. Nguyen, M. Marinelli, V. Neg- nevitsky, K. Mehta, and J. Home, Encoding a qubit in a trapped-ion mechanical oscillator, Nature566, 513 (2019)
work page 2019
- [29]
- [30]
-
[31]
I. Tzitrin, J. E. Bourassa, N. C. Menicucci, and K. K. Sabapathy, Progress towards practical qubit computa- tion using approximate gottesman-kitaev-preskill codes, Physical Review A101, 032315 (2020)
work page 2020
-
[32]
V. V. Albert, K. Noh, K. Duivenvoorden, D. J. Young, R. Brierley, P. Reinhold, C. Vuillot, L. Li, C. Shen, S. M. Girvin,et al., Performance and structure of single-mode bosonic codes, Physical Review A97, 032346 (2018)
work page 2018
-
[33]
S. Glancy and E. Knill, Error analysis for encoding a qubit in an oscillator, Physical Review A—Atomic, Molecular, and Optical Physics73, 012325 (2006)
work page 2006
- [34]
-
[35]
F. Rozpkedek, K. Noh, Q. Xu, S. Guha, and L. Jiang, Quantum repeaters based on concatenated bosonic and discrete-variable quantum codes, npj Quantum Informa- tion7, 102 (2021)
work page 2021
-
[36]
F. Schmidt, D. Miller, and P. van Loock, Error-corrected quantum repeaters with gottesman-kitaev-preskill qu- dits, Physical Review A109, 042427 (2024)
work page 2024
-
[37]
S. H¨ aussler and P. van Loock, Quantum repeaters based on stationary gottesman-kitaev-preskill qubits, Physical Review A111, 062611 (2025)
work page 2025
- [38]
-
[39]
J. J. Guanzon, M. S. Winnel, A. P. Lund, and T. C. Ralph, Ideal quantum teleamplification up to a selected energy cutoff using linear optics, Physical Review Letters 128, 160501 (2022)
work page 2022
- [40]
- [41]
- [42]
-
[43]
S. Muralidharan, J. Kim, N. L¨ utkenhaus, M. D. Lukin, and L. Jiang, Ultrafast and fault-tolerant quantum com- munication across long distances, Physical review letters 112, 250501 (2014)
work page 2014
-
[44]
S. L. Braunstein and P. Van Loock, Quantum infor- mation with continuous variables, Reviews of modern physics77, 513 (2005)
work page 2005
-
[45]
T. C. Ralph, A. Hayes, and A. Gilchrist, Loss-tolerant optical qubits, Physical review letters95, 100501 (2005)
work page 2005
-
[46]
B. W. Walshe, B. Q. Baragiola, R. N. Alexander, and N. C. Menicucci, Continuous-variable gate teleportation and bosonic-code error correction, Physical Review A 102, 062411 (2020)
work page 2020
-
[47]
T. Matsuura, H. Yamasaki, and M. Koashi, Equivalence of approximate gottesman-kitaev-preskill codes, Physical Review A102, 032408 (2020)
work page 2020
-
[48]
N. C. Menicucci, Fault-tolerant measurement-based quantum computing with continuous-variable cluster states, Physical review letters112, 120504 (2014)
work page 2014
-
[49]
K. Noh, V. V. Albert, and L. Jiang, Quantum capacity bounds of gaussian thermal loss channels and achievable rates with gottesman-kitaev-preskill codes, IEEE Trans- actions on Information Theory65, 2563 (2018)
work page 2018
-
[50]
K. Noh, S. Girvin, and L. Jiang, Encoding an oscilla- tor into many oscillators, Physical Review Letters125, 080503 (2020)
work page 2020
-
[51]
K. Duivenvoorden, B. M. Terhal, and D. Weigand, Single- mode displacement sensor, Physical Review A95, 012305 (2017)
work page 2017
-
[52]
M. V. Larsen, C. Chamberland, K. Noh, J. S. Neergaard- Nielsen, and U. L. Andersen, Fault-tolerant continuous- variable measurement-based quantum computation ar- chitecture, Prx Quantum2, 030325 (2021)
work page 2021
-
[53]
L. Z. Cohen, I. H. Kim, S. D. Bartlett, and B. J. Brown, Low-overhead fault-tolerant quantum computing using long-range connectivity, Science Advances8, eabn1717 (2022)
work page 2022
-
[54]
T. C. Ralph, M. S. Winnel, S. N. Swain, and R. J. Marsh- man, Noise transfer approach to gkp quantum circuits, Entropy26, 874 (2024)
work page 2024
-
[55]
M. Varnava, D. E. Browne, and T. Rudolph, Loss tol- erance in one-way quantum computation via counterfac- tual error correction, Physical review letters97, 120501 (2006)
work page 2006
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.