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  • 1.8
    Impact Factor
  • 2.7
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  • 21 days
    Submission to First Decision
  • 4 days
    Acceptance to Publication

Quantum Reports

Quantum Reports is an international, peer-reviewed, open access journal on quantum science. It publishes original research articles and review articles in all quantum subfields, from basic quantum theory to a broad array of applications. Quantum Reports is published quarterly online by MDPI.

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All Articles (434)

  • Systematic Review
  • Open Access

Quantum Machine Learning: An Experimental Survey

  • Erasmo Rivas,
  • James Resto and
  • Nabeel Alzahrani
  • + 2 authors

Quantum machine learning (QML) is advancing rapidly, yet it remains unclear which artificial intelligence (AI) capabilities benefit from quantum approaches, how strong the supporting evidence is, and whether reported gains justify claims of practical quantum advantage. This bounded critical survey introduces the Quantum AI Stack (QAIS), a capability-centered framework covering ten functional areas, and applies it to 107 experimental studies first released from 2024 to 6 August 2026, identified through keyword searches of arXiv, IEEE Xplore and the ACM Digital Library and reported following PRISMA 2020. Each study was appraised on seven weighted criteria, including comparison fairness, statistical practice, reproducibility and hardware realism, and each capability was assigned a level in a five-level maturity model. Within this corpus, quantum feature learning, quantum neural networks, hybrid quantum AI and quantum optimization have the most thoroughly corroborated evidence, much of it establishing parity rather than advantage, and no capability is deployable. Benefits that survive fair classical comparison are narrow and study-specific, including benchmark-specific accuracy gains and improvements in parameter efficiency, robustness, throughput and energy. None establishes practical quantum advantage, and null or negative findings occur at every level of evidence quality. Because inter-rater agreement was limited, the maturity assignments are provisional.

Quantum Rep.

12 November 2026

Minimum auditable systematic-review corpus flow. Stage 1 determines eligibility and fixes the 107-study corpus; Stage 2 appraises evidence strength without retroactively excluding eligible studies. Because per-database retrieval totals were not retained, the diagram begins at candidate identification and is not a complete database-to-inclusion reconstruction.
  • Article
  • Open Access

One century after Schrödinger’s 1926 papers, the optical–mechanical analogy remains a useful guide to wave mechanics. This pedagogical perspective connects action and phase, stationary states, superposition, field modes, and electromagnetic gauge coupling. Its contribution is a unified account that explicitly separates exact identities, controlled approximations, and heuristic analogies. We distinguish Fourier representations from independently evolving momentum modes, exhibit the assumptions required to recover Hamilton–Jacobi dynamics, and separate classical mode selection from canonical field quantization. Electromagnetic phase factors are presented with their domains of validity, while operational measurement rules are distinguished from interpretative claims. The article proposes neither new dynamics nor a resolution of the measurement problem; it offers a physically motivated route through established results while identifying where classical wave intuition ceases to be sufficient.

Quantum Rep.

12 November 2026

Wave–particle analogy. Light rays can be easily visualized as particle trajectories orthogonal to the light wavefront.
  • Article
  • Open Access

Quantum-network capacity planning couples memory physics, finite storage, topology, and traffic. We study these interactions with a discrete-event simulator and six representative memory profiles. The simulator is validated against exact single-link, queueing, and swap-ASAP results and against the native SeQUeNCe protocol stack. The native comparison shows that a shared-multiplexing convention used in earlier versions of the model overstates the capacity gain from additional memory, so we report a per-slot model as the primary analysis and the earlier conventions as a sensitivity arm. A single frozen campaign of 266,736 time-based runs with 20 seeds per cell covers an atlas of six profiles, nine topologies, three loads, three network sizes, and seven per-node memory budgets, together with fixed-total-memory, coherence-time, heterogeneous-placement, and Sobol-sensitivity experiments. Under the primary model, the memory budget at which completion reaches 95% of its observed maximum has a median of 8 slots per node, depends more on topology than on memory profile, and reaches the grid boundary of 64 slots in 3.9% of 9688 regimes. Under the earlier conventions, it is strongly profile-dependent, with medians from 4 to at least 64 and 45.8% boundary cases. Four scalar reductions do not collapse the response (pooled quadratic R2 at most 0.152). Topology effects persist at fixed total memory after adjustment for path length. Request completion is independent of the coherence time T2 by construction and is governed by retrieval efficiency, attempt time, and the retrieval decay time τr; T2 enters through fidelity-qualified service. The retrieval-window parameter orders the profiles by achievable completion but is not a memory-sizing law. Placing high-quality memories at hubs or betweenness bottlenecks outperforms peripheral placement in both model arms and under three interface-coupling rules. Memory-sizing conclusions are therefore sensitive to how multiplexing and storage are modeled and should be validated against native protocol implementations.

Quantum Rep.

10 November 2026

Key findings at a glance (primary model, v06 campaign). From left: 
  
    A
    req
  
 by topology (
  
    m
    =
    4
  
, 
  
    N
    =
    20
  
); pooled quadratic 
  
    R
    2
  
 of the four scalar candidates; distribution of the memory-budget threshold 
  
    m
    c
  
 at 
  
    α
    =
    0.95
  
, with boundary cases (
  
    
      m
      c
    
    =
    64
  
) in red; and 
  
    A
    req
  
 by placement strategy for high-quality memories. Error bars are 95% bootstrap intervals over seeds.
  • Article
  • Open Access

Mathematical similarities between Fokker–Planck diffusion, Schrödinger evolution and quantum measurement do not establish physical equivalence. We identify separate requirements for stationary-density matching, a shared spectral clock, quantum-state admissibility and measurement statistics. For harmonic gradient diffusion, matching a quantum ground-state position density fixes only the ratio of spatial diffusivity to relaxation rate. A common clock across independently identified modes additionally requires equal relaxation-to-frequency ratios, equivalently equal mass-weighted diffusivities. Two independently calibratable residuals distinguish these requirements; circulating Ornstein–Uhlenbeck countermodels retain the matched stationary marginals without satisfying the common-clock condition. A laboratory test requires an independently specified carrier in the strongly overdamped regime; none is identified here. We distinguish density Fisher information from quantum Fisher information, specify the phase structure needed for local Schrödinger evolution, and state Husimi-state and quantum-channel admissibility criteria. A previously published completely positive measurement instrument provides a benchmark for finite-time records and backaction. Its Born weights and threshold preparation are supplied inputs. Selected earlier Architecture of Distinction (AoD) identifications are also clarified and corrected. Neither the Born rule nor an individual outcome is derived, and no parameter-free departure from quantum mechanics is predicted.

Quantum Rep.

9 November 2026

Equal stationary position density does not imply equal dynamics. In units m = ω = ℏ = 1, the matched diffusion has γ = 0.35 and Dq = 0.175. Its normalized mean is e−0.35t; an isolated quantum coherent state with zero initial mean momentum has mean cost. These are analytic model curves, not experimental data. Equation (4) describes a massive carrier accurately only for γ/ω ≪ 1/2 (Section 3.2).

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Quantum Rep. - ISSN 2624-960X