Coherence dynamics in Simon's quantum algorithm

Linlin Ye, Zhaoqi Wu, Shao-Ming Fei

#2562 of 2593 · Quantum Physics
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Tournament Score
1197±32
10501750
13%
Win Rate
7
Wins
47
Losses
54
Matches
Rating
2.5/ 10
Significance
Rigor
Novelty
Clarity

Abstract

Quantum coherence plays a pivotal role in quantum algorithms. We study the coherence dynamics of the evolved states in Simon's quantum algorithm based on Tsallis relative αα entropy and l1,pl_{1,p} norm. We prove that the coherences of the first register and the second register both rely on the dimension NN of the state spaces of the nn qubit systems, and increase with the increase of NN. We show that the oracle operator OO does not change the coherence. Moreover, we study the coherence dynamics in the Simon's quantum algorithm and prove that in overall the coherence is in production when N>4N>4 and in depletion when N<4N<4.

AI Impact Assessments

(3 models)

Scientific Impact Assessment: "Coherence dynamics in Simon's quantum algorithm"

1. Core Contribution

This paper analyzes the quantum coherence dynamics of evolved states throughout Simon's quantum algorithm, using two coherence quantifiers: the Tsallis relative α entropy and the l_{1,p} norm. The main claims are:

  • The coherence of the first and second registers depends on the dimension N = 2^n and increases with N.
  • The oracle operator O preserves coherence.
  • The overall coherence variation is positive (coherence production) when N > 4 and negative (coherence depletion) when N < 4.
  • The paper follows a template established by prior works studying coherence dynamics in other quantum algorithms (e.g., Grover's algorithm, Deutsch-Jozsa), now applied to Simon's algorithm.

    2. Methodological Rigor

    The mathematical derivations are straightforward calculations. The authors compute density matrices at each step of Simon's algorithm (after Hadamard, after oracle, after second Hadamard) and plug them into known coherence formulas. The proofs are direct substitutions — for instance, Theorem 1 simply evaluates the Tsallis coherence measure on the uniform superposition state ρ_H = (1/2^n) Σ_{x,y} |x⟩⟨y|, which is a standard pure state with well-known properties.

    Several concerns arise regarding rigor:

  • Trivial nature of key results: The finding that the oracle O preserves coherence (Theorem 2) follows immediately from the fact that O is a unitary permutation operator acting on the computational basis of the full system. The coherence is computed on the global state, and unitary operations that merely relabel computational basis states while maintaining the same superposition structure will naturally preserve coherence measures. This is not deeply insightful.
  • The N > 4 vs N < 4 threshold: The result that coherence is produced when N > 4 and depleted when N < 4 is presented as a central finding, but its significance is unclear. N = 4 corresponds to n = 2 qubits, and Simon's algorithm is only meaningful for n ≥ 2 (since n = 1 is trivial). So essentially, for all non-trivial instances except n = 2, coherence is produced. The threshold appears to be an artifact of comparing coherence at different stages rather than revealing deep structure.
  • Limited analysis scope: The paper only analyzes coherence of the global pure state, not reduced states of individual registers (despite claiming to study "first register and second register"). For a pure state, coherence is entirely determined by the superposition structure in the chosen basis, and many of the results follow from counting non-zero off-diagonal elements.
  • Examples are routine: Examples 1 and 2 merely verify the general formulas for N = 4 and N = 8, adding no additional insight.
  • 3. Potential Impact

    The practical and theoretical impact of this work is limited:

  • The results are descriptive rather than prescriptive — they characterize coherence at each step but do not explain *why* Simon's algorithm achieves exponential speedup in terms of coherence, nor do they establish any operational connection between coherence and the algorithm's performance.
  • No connection is drawn between coherence dynamics and the success probability or query complexity of the algorithm.
  • The paper does not compare coherence consumption/production across different quantum algorithms in a meaningful way that might yield general principles.
  • No experimental implications or applications are suggested.
  • 4. Timeliness & Relevance

    The study of quantum resources (coherence, entanglement) in quantum algorithms is a legitimate research direction, but this particular paper arrives relatively late in the cycle. Similar analyses for Grover's algorithm, Deutsch-Jozsa, and Bernstein-Vazirani have been published years ago (refs [38-40]). The extension to Simon's algorithm, while filling a gap, does not introduce new methodology or conceptual advances.

    The coherence measures used (Tsallis relative α entropy, l_{1,p} norm) are known quantities, and the paper does not leverage any special properties of these measures that would be unavailable with simpler measures like relative entropy of coherence or l_1 norm.

    5. Strengths & Limitations

    Strengths:

  • Complete and systematic: The paper tracks coherence through every step of the algorithm.
  • Multiple coherence measures are employed, providing some breadth.
  • The mathematical presentation is clear and self-contained.
  • Limitations:

  • Shallow analysis: Results follow from direct calculation without deeper insight into the role of coherence as a computational resource.
  • No operational significance: There is no connection established between coherence dynamics and algorithmic performance or advantage.
  • Incremental contribution: The work mechanically applies known coherence measures to another quantum algorithm, following an established template.
  • Missing reduced-state analysis: Coherence of reduced states (partial traces) would be more informative about the algorithm's structure than global pure-state coherence.
  • No comparison with classical resources: The paper does not address what the coherence dynamics tell us about the quantum-classical gap that Simon's algorithm exemplifies.
  • Writing quality: The paper is quite short (effectively ~5 pages of content) and reads more like a technical note than a full research paper. The conclusion's claim that results "may shed new light on the study of coherence dynamics in other quantum algorithms" is unsubstantiated.
  • Overall Assessment

    This paper represents a routine application of existing coherence measures to track coherence through the steps of Simon's quantum algorithm. While mathematically correct, the results are largely unsurprising and lack the depth needed to advance our understanding of the role of coherence in quantum computation. The paper does not establish any operational connection between coherence and algorithmic performance, making the analysis primarily descriptive. The contribution is incremental and of limited impact.

    Rating:2.5/ 10
    Significance 2Rigor 4.5Novelty 2Clarity 5.5

    Generated Apr 20, 2026

    Comparison History (54)

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