REVIEW 3 major objections 5 minor 53 references
Holographic quantum error-correcting codes have been realized on a trapped-ion processor, with bulk qubits recovered from boundary regions and the Ryu-Takayanagi entanglement area law measured in the laboratory.
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 · deepseek-v4-flash
2026-08-01 20:45 UTC pith:MAVCQVXM
load-bearing objection First real laboratory implementations of holographic pentagon and heptagon codes, with genuinely new decoding circuits and a quasi-transversal Hadamard gate; the experimental work deserves a serious referee, but the RT-law test is quantitatively unsupported as written. the 3 major comments →
Holographic quantum codes with trapped ions
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The paper establishes, on its own terms, that holographic quantum error correction can be brought into the laboratory. A small pentagon code—built from four six-qubit absolutely maximally entangled states—successfully encodes four bulk qubits into twelve boundary qubits, and logical information can be recovered from boundary subregions alone: two bulk qubits from five boundary qubits, three from seven, and four from eight. The measured von Neumann entropies of the boundary regions are 3.96(2), 4.13(2), and 3.818(10), close to the ideal values 3, 4, and 4 predicted by the Ryu-Takayanagi formula. For the heptagon code, formed by contracting two seven-qubit CSS codes, the transversal Hadamard o
What carries the argument
The load-bearing object is the stabilizer graph-code representation of the tensor-network holographic code: the code state |G0000> is a graph state prepared by applying 28 controlled-Z gates to twelve |+> qubits, and the graph structure supplies the logical operators and the decoding circuits. The six-qubit absolutely maximally entangled states—states where every half is maximally entangled with its complement—act as the pentagon building blocks. A decoding cut is implemented by a unitary built from concatenated AME states, each expressed as a three-to-three-qubit unitary extracted from the graph code. The Ryu-Takayanagi formula enters as S(∂E) = |γ|, equating the entropy of a boundary regio
Load-bearing premise
Everything holographic rests on the claim that the graph-code representation used in the experiments reproduces the original tensor-network holographic code exactly, including which boundary regions can recover which bulk regions; if that equivalence fails for the chosen cuts, the observed partial-recovery regions and entropies would not demonstrate holography.
What would settle it
Simulate the original tensor-network pentagon code directly for cuts 1–3 and compare the partial-recovery maps and boundary entropies with the graph-code circuits used here; if any of the 2-, 3-, or 4-qubit recovery maps fail to act as the claimed isometries, or if the entropy departs from |γ| beyond depolarizing-noise expectations, the holographic interpretation is undermined. For the heptagon code, verify that the sign flip of the product g5g10 after the physical Hadamard is the only induced error; finding a second uncorrectable error would falsify the quasi-transversal claim.
If this is right
- The heptagon result provides a template for logical gates in holographic codes: a gate that is transversal in the constituent code may induce only a single correctable error in the glued code, so a short round of error correction restores fault-tolerant operation.
- Partial decoding from a confined boundary region means holographic codes can protect information even when large parts of the quantum processor are inaccessible or noisy, a property relevant for burst errors.
- The measured entropies support the Ryu-Takayanagi area law in a finite-size code, connecting laboratory data to a formula originally motivated by quantum gravity.
- Unique syndrome tables and a code distance of three mean the implemented pentagon instance can serve as a small geometric quantum error-correcting memory.
- The quasi-transversal Hadamard with Pauli-frame correction is a concrete fault-tolerance primitive; extending it to a full set of logical gates would be the next step toward holographic quantum computation.
Where Pith is reading between the lines
- Editorial inference: if the graph-code equivalence holds, the same extraction method should scale to larger hyperbolic tilings; a natural test is to verify that the measured boundary entropy remains linear in the cut length as the tiling depth increases.
- Editorial inference: the burst-error discussion suggests holographic codes may outperform block codes on spatially correlated noise; a direct experiment injecting adjacent two- and three-qubit errors and comparing with the constituent seven-qubit code would test this advantage.
- Editorial inference: the quasi-transversal mechanism may generalize to a design rule—transversal in the constituent block, correctable in the glued code—that could guide the construction of fault-tolerant gate sets for other holographic or concatenated codes.
- Editorial inference: the corrections here are applied in post-processing via Pauli-frame updates; implementing them in real time would test whether holographic codes can support active, hardware-level error correction.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper reports trapped-ion experiments on small instances of holographic pentagon and heptagon codes. The pentagon-code experiment prepares graph-code states, measures stabilizers and logical operators, detects single-qubit errors, performs partial decoding of two, three, and four bulk qubits from boundary regions, and measures tomographic entropies that are compared with the Ryu-Takayanagi formula. The heptagon-code experiment initializes a two-logical-qubit code, applies logical operations, and demonstrates a quasi-transversal Hadamard gate whose induced error is corrected by a Pauli-frame update. All data are compared with a depolarizing-noise simulation.
Significance. If the claims are substantiated, this would be one of the first laboratory implementations of holographic quantum codes, with partial bulk-to-boundary decoding, an RT-type entropy law, and a quasi-transversal logical Hadamard gate. The paper benefits from using an external trapped-ion hardware benchmark and from grounding the code construction in the published graph-code framework of Ref. [23]. The most valuable evidence is the state-preparation stabilizer data, which lie above the mixed-state threshold, and the syndrome look-up table. However, the two headline results—'recovering logical bulk qubits' and 'testing the RT area law'—are not yet quantitatively supported, as detailed below.
major comments (3)
- [Entropy measurement (Pentagon code), Eq. (4)] The RT-law claim is not quantitatively supported. The measured entropies are 3.96(2) vs ideal 3 (cut 1), 4.13(2) vs ideal 4 (cut 2), and 3.818(10) vs ideal 4 (cut 3). These are deviations of +0.96, +0.13, and -0.18 bits, many standard deviations from the prediction. The text explains cut 1 by a 'finite upper bound in entropy' and cut 3 by residual pure-state contributions, but no noisy simulation of the entropy is provided; Supp. SX compares tomography only to a noise-free simulation. Since Eq. (4) is the central prediction being tested, a quantitative error budget is needed before 'testing the RT area law' can be claimed.
- [Partial decoding, §II.A and Supp. SIX] The decoded-qubit expectation values are far below the ideal value of +1 and in several cases disagree with the depolarizing simulation at many standard deviations. For cut 1, A=0.616(15) vs sim 0.436(16) and B=0.296(14) vs sim 0.422(16); for cut 3, B=0.142(11) vs sim 0.103(9). A logical Z-expectation near 0.3 means the recovered state is nearly random in that basis. The statement that the decoding 'reliably recovers the encoded logical qubits' is therefore not supported by the data as presented. Please provide a fidelity or process metric and address the simulation mismatch.
- [Fig. 3 caption and Supp. SVIII] The holographic interpretation relies on the claim that the graph code of Fig. 2(b) is, up to local Clifford operations, equivalent to the directly contracted tensor network. The paper does not give the explicit Clifford transformation or show that it preserves the partial-recovery regions and the RT formula for the cuts used. Since the decoding circuits are built from the graph code, this equivalence is load-bearing for the holographic claims. Please provide a derivation or a precise reference to the proof.
minor comments (5)
- [Heptagon code, §II.B] Typo: 'sate preparation' should be 'state preparation'.
- [Fig. 5(c) caption] Typo: 'the the graph code' should be 'the graph code'.
- [Supplementary material] The numbering is inconsistent: 'Supp. Mat. SIX' is used for the decoding expectation values, while 'Supp. Mat. SX' is used for the tomography. Please renumber for clarity.
- [Fig. 6 caption] The caption labels the induced gate as 'RXX 6,11' while the text says the MS gate is applied between qubits 6 and 11. Please make the notation consistent.
- [Data availability] The data availability statement says data can be made available on request. Given the complexity of the tomography and decoding data, a permanent public repository would improve reproducibility.
Circularity Check
No significant circularity: the experimental claims are benchmarked against external hardware and prior published code constructions; no measured quantity is fitted and repackaged as a prediction.
full rationale
The paper's derivation chain is: (i) take the HaPPY pentagon code [9] and heptagon CSS code [12], (ii) use the graph-code representation of [23] (which the paper states is Clifford-equivalent to the tensor-network contraction) to construct preparation and decoding circuits, (iii) measure stabilizers, logical operators, decoded qubit expectation values, and reduced-state entropies on a trapped-ion processor, and (iv) compare to a depolarizing-noise simulation with error rates p1=0.005, p2=0.025 taken from prior hardware characterization [28]. No step fits a free parameter to the target observable and then reports it as a prediction. The partial-recovery circuits are derived from the stabilizer/graph structure, not from the measured data; the RT 'ideal' values |gamma| are counts of contracted indices, not fitted constants. The observed deviations from the RT prediction (e.g., 3.96(2) vs 3) are a quantitative verification issue, not circularity. The main caveat is that the holographic interpretation relies on the Clifford-equivalence assertion from [23], which is co-authored by current authors; however, that assertion is a mathematical tool with stated assumptions independent of the present measurements, so it is prior evidence rather than a circular premise. No equation reduces to its input by construction.
Axiom & Free-Parameter Ledger
free parameters (2)
- single-qubit depolarizing error rate p1 =
0.005
- two-qubit depolarizing error rate p2 =
0.025
axioms (5)
- standard math Stabilizer formalism and graph-state code basis
- domain assumption HaPPY pentagon/AME tensor-network code satisfies partial-recovery and RT formula for the chosen cuts
- domain assumption Graph code of [23] is equivalent up to local Clifford to the tensor-network holographic code
- ad hoc to paper Depolarizing noise model captures experimental errors
- domain assumption Pauli-frame update suffices to correct the stabilizer sign flip induced by the logical Hadamard
Cite this review
Pith. "Pith review of Holographic quantum codes with trapped ions." pith.science (2026). https://pith.science/paper/MAVCQVXM
@misc{pith2026260716503,
author = {Pith},
title = {Pith review of: Holographic quantum codes with trapped ions},
year = {2026},
howpublished = {\url{https://pith.science/paper/MAVCQVXM}},
note = {Machine review of arXiv:2607.16503}
}
read the original abstract
Holography is a central concept at the intersection of gravity, condensed matter theory, and quantum information, linking the interior bulk of a system to its boundary. A model realizing key features of holographic systems is the holographic pentagon code by Pastawski et al. Here we experimentally implement instances of the holographic pentagon and heptagon codes with trapped ions and test their properties: For the pentagon code, we recover logical bulk qubits from their nearby boundary and test the Ryu-Takayanagi entanglement area law. For the heptagon code, we show that the transversal Hadamard gate native to the constituent Steane codes induces a single-qubit, correctable error in the holographic code. Our implementation paves the way towards the use of holographic quantum codes for quantum information processing.
Figures
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The Z-part (the three right columns) of the rows in R in Eq. (S40) corresponds to ΓZ, since performing row operations on (D|G|0 ⊺) results in (1 k|ΓZ|0⊺). As a consequence,E Z ={(12),(23)}. The encoding gates are also illustrated in Fig. 3(c). Supplementary SVIII: Alternative partial decoding In this paper, we perform a partial decoding procedure that dif...
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The error bars are computed from quantum projection noise and represent one standard deviation of statistical uncertainty
Blue bars correspond to experimental data while the orange bars correspond to numerical simulation. The error bars are computed from quantum projection noise and represent one standard deviation of statistical uncertainty. The im- plementation of the Hadamard gate on logical qubitAis followed by post selecting the sign of stabilizer generators g5 andg 10 ...
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3(b)-(c)
(S44) as illustrated in Fig. 3(b)-(c). As in Ref. [23], one needs to further modifyU † h to par- tially decode a state that is encoded via the used graph code. This requires the addition of a Hadamard gate that leads to eU † h =U hH3. The decoding circuit is shown in Fig. 3(c). The partial decoding operator requires 14 two-qubit gates and 7 one-qubit gate...
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