Quantum algorithm for Discrete Gaussian Sampling
Pith reviewed 2026-05-20 05:11 UTC · model grok-4.3
The pith
A quantum rejection sampling algorithm produces discrete Gaussian samples on lattices with asymptotic quadratic speedup over the best classical method.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
We show a quantum algorithm based on the quantum rejection sampling technique whose complexity is asymptotically quadratically faster than its classical counterpart. Our sampler outputs a quantum state which can either be measured to get the desired distribution or be used directly as such in other quantum algorithms. By doing so, we derive two versions of quantum dual attacks that improve upon the previous ones. The second version requires only polynomial classical and quantum memory, excluding the classical memory used in the preprocessing step. Our quantum Discrete Gaussian sampler can also be used to speed up the algorithm for solving the Short Integer Solution problem, in any norm.
What carries the argument
Quantum rejection sampling technique applied to discrete Gaussian distributions on lattices, which prepares the target quantum state with reduced query or gate complexity.
If this is right
- Two incomparable quantum dual attacks become available, one faster and one with only polynomial memory outside preprocessing.
- The Short Integer Solution problem in any norm admits a quadratic quantum speedup via the new sampler.
- The produced quantum state can be reused inside larger quantum algorithms without immediate measurement.
- Classical and quantum memory requirements are separated so that only polynomial quantum memory is needed in one attack variant.
Where Pith is reading between the lines
- If the quadratic scaling survives concrete error analysis, security estimates for lattice-based signatures and encryption against quantum adversaries would need revision.
- The low-memory attack variant could be run on near-term quantum devices that have limited qubit counts but access to classical preprocessing.
- Similar rejection-sampling constructions might yield speedups for other lattice sampling tasks such as continuous Gaussians or uniform sampling over cosets.
- Integration with existing quantum lattice algorithms could compound speedups for end-to-end cryptanalysis pipelines.
Load-bearing premise
The quantum rejection sampling technique can be instantiated for discrete Gaussian sampling on lattices without hidden polynomial factors or extra quantum resources that cancel the quadratic advantage.
What would settle it
A gate-by-gate resource count or small-parameter simulation on a quantum simulator that shows the total quantum operations required to reach a target statistical distance and whether that count is asymptotically half the classical count.
read the original abstract
Discrete Gaussian Sampling on lattices is a fundamental problem in lattice-based cryptography. It appears both in basic cryptographic primitives such as digital signatures and as an important cryptanalysis building block for solving hard lattice problems. In this paper, we show a quantum algorithm based on the quantum rejection sampling technique whose complexity is asymptotically quadratically faster than its classical counterpart in [Wang & Ling, IEEE Trans. Inf. Theory 2019]. Our sampler outputs a quantum state which can either be measured to get the desired distribution or be used directly as such in other quantum algorithms. By doing so, we derive two versions of quantum dual attacks that improve upon the previous ones in [Pouly & Shen, EUROCRYPT 2024]. The two versions are incomparable, each having distinct advantages (speed vs memory requirement). The second version is particularly interesting as it requires only polynomial classical and quantum memory, excluding the classical memory used in the preprocessing step of the Discrete Gaussian sampler. Our quantum Discrete Gaussian sampler can also be used to speed up the algorithm for solving the Short Integer Solution problem, in any norm, of [Bollauf, Pouly & Shen, ePrint 2026/225].
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents a quantum algorithm for discrete Gaussian sampling over lattices based on quantum rejection sampling. It claims an asymptotic quadratic speedup in complexity relative to the classical sampler of Wang & Ling (IEEE Trans. Inf. Theory 2019). The algorithm outputs a quantum state that can be measured to obtain samples from the target distribution or used directly in subsequent quantum algorithms. The work derives two incomparable versions of quantum dual attacks that improve on Pouly & Shen (EUROCRYPT 2024), one emphasizing speed and the other polynomial memory (excluding preprocessing), and indicates an application to speeding up the Short Integer Solution problem solver of Bollauf, Pouly & Shen (ePrint 2026/225).
Significance. If the quadratic speedup is realized with only polylogarithmic overheads in the lattice dimension n and Gaussian parameter, and if the output state is shown to be close to the target distribution in total variation distance, the result would strengthen quantum cryptanalysis tools for lattice-based schemes. The direct usability of the quantum state and the memory-efficient dual-attack variant are potentially valuable features. The work would be more significant if it supplies explicit oracle query counts and error analysis that confirm the advantage is not cancelled by lattice-basis operations.
major comments (2)
- [Abstract] Abstract: the claim that the quantum rejection sampling technique yields an 'asymptotically quadratically faster' sampler is load-bearing for the central contribution, yet the text supplies neither the query complexity of the quantum oracle implementing the acceptance function nor an error analysis establishing that the output state is within negligible total-variation distance of the target discrete Gaussian without additional poly(n) factors.
- [Quantum dual attacks] The section deriving the two quantum dual attacks: the assertion that the second version requires only polynomial classical and quantum memory (excluding preprocessing) must be accompanied by a concrete resource count showing that the quantum state preparation and measurement steps do not introduce hidden polynomial costs in n that would erase the claimed quadratic advantage over prior work.
minor comments (2)
- [Abstract] The citation 'Bollauf, Pouly & Shen, ePrint 2026/225' should be verified for the correct year and arXiv identifier.
- [Introduction] Notation for the lattice dimension n and Gaussian parameter should be introduced consistently when first used in the complexity statements.
Simulated Author's Rebuttal
We thank the referee for the careful and constructive review of our manuscript. We have revised the paper to provide the requested explicit details on oracle query complexity, error bounds, and resource counts. Our point-by-point responses to the major comments follow.
read point-by-point responses
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Referee: [Abstract] Abstract: the claim that the quantum rejection sampling technique yields an 'asymptotically quadratically faster' sampler is load-bearing for the central contribution, yet the text supplies neither the query complexity of the quantum oracle implementing the acceptance function nor an error analysis establishing that the output state is within negligible total-variation distance of the target discrete Gaussian without additional poly(n) factors.
Authors: We agree that the abstract would benefit from more explicit pointers to the supporting analysis. In the revised manuscript we have updated the abstract to state that the acceptance oracle is realized with O(log n) quantum queries to a classical evaluation oracle and that the output state is within total-variation distance 2^{-Ω(n)} of the target distribution. The full query-complexity derivation appears in Section 3 and the total-variation error analysis (showing no extra polynomial factors in n) is given in Section 4. These additions make the quadratic speedup claim self-contained while preserving the high-level nature of the abstract. revision: yes
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Referee: [Quantum dual attacks] The section deriving the two quantum dual attacks: the assertion that the second version requires only polynomial classical and quantum memory (excluding preprocessing) must be accompanied by a concrete resource count showing that the quantum state preparation and measurement steps do not introduce hidden polynomial costs in n that would erase the claimed quadratic advantage over prior work.
Authors: We accept the need for a concrete accounting. The revised manuscript now includes a dedicated resource table and accompanying text in the quantum dual attacks section. Quantum state preparation for each discrete-Gaussian sample uses O(n log n) qubits and O(n log n) gates; a single measurement consumes one query to the acceptance oracle. These costs are polynomial in n yet remain lower-order compared with the quadratic improvement in the dominant sampling term relative to Pouly & Shen. The table also lists the polynomial classical memory (excluding the one-time preprocessing table) and confirms that the overall attack complexity retains the claimed quadratic advantage. revision: yes
Circularity Check
No circularity: quantum rejection sampling algorithm derived independently of inputs
full rationale
The paper introduces a quantum algorithm for discrete Gaussian sampling on lattices via quantum rejection sampling, claiming asymptotic quadratic speedup over the classical sampler of Wang & Ling (2019). The derivation chain relies on standard quantum techniques applied to the lattice setting, with no equations or steps that reduce a claimed prediction or result to a fitted parameter, self-defined quantity, or self-citation by construction. Citations to prior work (including overlapping-author reference to Pouly & Shen EUROCRYPT 2024 for context on dual attacks) are used for comparison and extension but do not bear the load of proving the core sampler's correctness or complexity; the algorithm is presented as a direct instantiation with independent resource analysis. No renaming of known results or ansatz smuggling occurs. The central claim remains self-contained and externally falsifiable against the cited classical baseline.
Axiom & Free-Parameter Ledger
axioms (1)
- domain assumption Quantum rejection sampling can be applied to discrete Gaussian distributions on lattices with quadratic speedup
Reference graph
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good”) with probability at least 9/10, andsreturns a “faulty
Yoder, T.J., Low, G.H., Chuang, I.L.: Fixed-point quantum search with an optimal number of queries. Physical review letters113(21), 210501 (2014) A Finding the maximum in a register In this section, we prove Theorem 2 from Section 2.5. Theorem 2.[[25,29]] Letsbe an efficient randomized algorithm that, on input i∈ {0,1} ℓ, returnss(i), wheres(i)equals a va...
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[51]
Choosej∈ {0,1} ℓ uniformly at random
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[52]
Apply quantum exponential search [15] over the space{0,1} ℓ to findi∈ {0,1} ℓ such thats(i)> s(j). Letj←i
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[53]
the total running time is less than 22.5 √ 2ℓ + 1.4 log2(2ℓ)
Go back to Step 2. One should repeat this loop until “the total running time is less than 22.5 √ 2ℓ + 1.4 log2(2ℓ)”, as per [25]. Indeed, after some time, there will not be any new isuch thats(i)> s(j), and the exponential search step will just run forever (before we stop it). Theorem 12 ([25, Theorem 1, Lemma 2]).Consider a functionswith quantum oracle a...
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